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CLASSIFICATION CANCELLED 
por memorandum, Ac tins Secretary of 
>fense, .aaced 'Aug. 2, I960, / 

%£>. . . l^UljjSLK 





SUMMARY TECHNICAL REPORT 

OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 


This document contains information affecting the national defense of the 
United States within the meaning of the Espionage Act, 50 U.S.C., 31 and 32, 
as amended. Its transmission or the revelation of its contents in any manner 
to an unauthorized person is prohibited by law. 

This volume is classified CONFIDENTIAL in accordance with security regu¬ 
lations of the War and Navy Departments because certain chapters contain 
material which was CONFIDENTIAL at the date of printing. Other chapters 
may have had a lower classification or none. The reader is advised to consult 
the War and Navy agencies listed on the reverse of this page for the current 
classification of any material. 









Manuscript and illustrations for this volume were prepared for 
publication by the Summary Reports Group of the Columbia 
University Division of War Research under Contract OEMsr-1131 
with the Office of Scientific Research and Development. This 
volume was printed and bound by the Columbia University Press. 

Distribution of the Summary Technical Report of NDRC has been 
made by the War and Navy Departments. Inquiries concerning the 
availability and distribution of the Summary Technical Report 
volumes and microfilmed and other reference material should be 
addressed to the War Department Library, Room 1A-522, The 
Pentagon, Washington 25, D. C., or to the Office of Naval Re¬ 
search, Navy Department, Attention: Reports and Documents 
Section, Washington 25, D. C. 


Copy No. 

235 


This volume, like the seventy others of the Summary Technical 
Report of NDRC, has been written, edited, and printed under 
great pressure. Inevitably there are errors which have slipped past 
Division readers and proofreaders. There may be errors of fact not 
known at time of printing. The author has not been able to follow 
through his writing to the final page proof. 

Please report errors to: 

JOINT EESEAECH AND DEVELOPMENT BOAED 
PEOGEAMS DIVISION (STE EEEATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports and sent 
to recipients of the volume. Your help will make this book more 
useful to other readers and will be of great value in preparing any 
revisions. 



SUMMARY TECHNICAL REPORT OF DIVISION 2 , NDRC 


VOLUME 1 

EFFECTS OF IMPACT 
AND EXPLOSION 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 

VANNEVAR BUSH, DIRECTOR 

NATIONAL DEFENSE RESEARCH COMMITTEE 

JAMES B. CONANT, CHAIRMAN 

DIVISION 2 

E. BRIGHT WILSON, JR., CHIEF 


WASHINGTON, D. C., 1946 







NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative 1 

Frank B. Jewett Navy Representative 2 

Karl T. Compton Commissioner of Patents 3 

Irvin Stewart, Executive Secretary 


1 Ar?ny representatives in order of service: 


Maj. Gen. G. V. Strong 
Maj. Gen. R. C. Moore 
Maj. Gen. C. C. Williams 
Brig. Gen. W. A. Wood, Jr. 

Col. E. 


Col. L. A. Denson 
Col. P. R. Faymonville 
Brig. Gen. E. A. Regnier 
Col. M. M. Irvine 
A. Routheau 


2 Navy representatives in order of service: 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 

Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 

Commodore H. A. Schade 

3 Commissioners of Patents in order of service: 

Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suitable 
projects and research programs on the instrumentalities of 
warfare, together with contract facilities for carrying out these 
projects and programs, and (2) to administer the technical 
and scientific work of the contracts. More specifically, NDRC 
functioned by initiating research projects on requests from 
the Army or the Navy, or on requests from an allied govern¬ 
ment transmitted through the Liaison Office of OSRD, or on 
its own considered initiative as a result of the experience of 
its members. Proposals prepared by the Division, Panel, or 
Committee for research contracts for performance of the 
work involved in such projects were first reviewed by NDRC, 
and if approved, recommended to the Director of OSRD. 
Upon approval of a proposal by the Director, a contract per¬ 
mitting maximum flexibility of scientific effort was arranged. 
The business aspects of the contract, including such matters 
as materials, clearances, vouchers, patents, priorities, legal 
matters, and administration of patent matters were handled 
by the Executive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were: 

Division A—Armor and Ordnance 

Division B—Bombs, Fuels, Gases, & Chemical Problems 
Division C—Communication and Transportation 
Division D—Detection, Controls, and Instruments 
Division E—Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three ad¬ 
ministrative divisions, panels, or committees were created, 
each with a chief selected on the basis of his outstanding 
work in the particular field. The NDRC members then be¬ 
came a reviewing and advisory group to the Director of 
OSRD. The final organization w'as as follow's: 


Division 1—Ballistic Research 

Division 2—Effects of Impact and Explosion 

Division 3—Rocket Ordnance 

Division 4—Ordnance Accessories 

Division 5—New r Missiles 

Division 6—Sub-Surface Warfare 

Division 7—Fire Control 

Division 8—Explosives 

Division 9—Chemistry 

Division 10—Absorbents and Aerosols 

Division 11—Chemical Engineering 

Division 12—Transportation 

Division 13—Electrical Communication 

Division 14—Radar 

Division 15—Radio Coordination 

Division 16—Optics and Camouflage 

Division 17—Physics 

Division 18—War Metallurgy 

Division 19—Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


\ 







NDRC FOREWORD 


As events of the years preceding 1940 revealed more 
•TA. and more clearly the seriousness of the world 
situation, many scientists in this country came to 
realize the need of organizing scientific research for 
service in a national emergency. Recommendations 
which they made to the White House were given care¬ 
ful and sympathetic attention, and as a result the 
National Defense Research Committee [NDRC] was 
formed by Executive Order of the President in the 
summer of 1940. The members of NDRC, appointed 
by the President, were instructed to supplement the 
work of the Army and the Navy in the development 
of the instrumentalities of war. A year later, upon the 
establishment of the Office of Scientific Research and 
Development [OSRD], NDRC became one of its units. 

The Summary Technical Report of NDRC is a 
conscientious effort on the part of NDRC to summa¬ 
rize and evaluate its work and to present it in a useful 
and permanent form. It comprises some seventy vol¬ 
umes broken into groups corresponding to the NDRC 
Divisions, Panels, and Committees. 

The Summary Technical Report of each Division, 
Panel, or Committee is an integral survey of the work 
of that group. The first volume of each group’s report 
contains a summary of the report, stating the problems 
presented and the philosophy of attacking them, and 
summarizing the results of the research, development, 
and training activities undertaken. Some volumes may 
be “state of the art” treatises covering subjects to 
which various research groups have contributed in¬ 
formation. Others may contain descriptions of devices 
developed in the laboratories. A master index of all 
these divisional, panel, and committee reports which 
together constitute the Summary Technical Report 
of NDRC is contained in a separate volume, which 
also includes the index of a microfilm record of per¬ 
tinent technical laboratory reports and reference 
material. 

Some of the NDRC-sponsored researches which had 
been declassified by the end of 1945 were of sufficient 
popular interest that it was found desirable to report 
them in the form of monographs, such as the series 
on radar by Division 14 and the monograph on sam¬ 
pling inspection by the Applied Mathematics Panel. 


Since the material treated in them is not duplicated 
in the Summary Technical Report of NDRC, the 
monographs are an important part of the story of 
these aspects of NDRC research. 

In contrast to the information on radar, which is 
of widespread interest and much of which is released 
to the public, the research on subsurface warfare is 
largely classified and is of general interest to a more 
restricted group. As a consequence, the report of 
Division 6 is found almost entirely in its Summary 
Technical Report, which runs to over twenty volumes. 
The extent of the work of a division cannot therefore 
be judged solely by the number of volumes devoted 
to it in the Summary Technical Report of NDRC; 
account must be taken of the monographs and avail¬ 
able reports published elsewhere. 

The research program of Division 2, first under the 
leadership of John E. Burchard and then of E. Bright 
Wilson, Jr., included studies of underwater explosions, 
of muzzle blast effects in high velocity guns, the ter¬ 
minal ballistics of concrete and plastic armor, and 
defenses against shaped-charge projectiles, to name 
but a few of the projects described in the Division’s 
Summary Technical Report, which has been prepared 
under the direction of the Division Chief and has been 
authorized by him for publication. 

The most dramatic example of the work of Division 
2 was the study of bombs of the blockbuster type. 
The blockbuster was the exclamation point to a pro¬ 
gram of research aimed at establishing principles for 
the selection of weapons designed to achieve maximum 
damage against a given target for a given expenditure 
of energy. The Division’s study on the effects of explo¬ 
sions in various types of soil is a project of great im¬ 
portance to a work in which any next war may involve 
atomic bombs and guided missiles. We join the nation 
in expressing gratitude for Division 2’s valuable war¬ 
time achievements. 

Vannevar Bush, Director 
Office of Scientific Research and Development 

J. B. Conant, Chairman 
National Defense Research Committee 


CONFIDENTIAL % 
































FOREWORD 


T he principal objective of Division 2 was to place 
the use of weapons and of defensive materials on a 
quantitative, engineering basis. Scientific studies were 
therefore carried out on terminal ballistics, on explo¬ 
sions in air, earth, and water, and on certain properties 
of materials, with the object of providing the basic 
data necessary for the rational employment of bombs, 
projectiles, explosives, etc. At all times, the principle 
was kept uppermost that practical results would inevi¬ 
tably follow from a deeper scientific understanding of 
the physics and chemistry of the phenomena involved 
in the action of weapons. 

It is hoped that the present volume will be useful 
to those groups who are carrying on work dealing with 
the design or employment of weapons. It should also 
be useful in the event of a future war in giving new¬ 
comers to the field a concise survey of the state of 
knowledge at the end of World War II. 

The field of activity of Division 2 touched upon 
those of several other divisions, particularly Division 
1, Ballistic Research, Division 8, Explosives, Division 
11, Chemical Engineering, Division 17, Physics, Divi¬ 
sion 18, War Metallurgy, and the Applied Mathematics 
Panel. The work on the terminal ballistics of hyper- 
velocity projectiles carried out at Princeton was natur¬ 
ally of importance to Division 1, which was developing 
means for producing these high velocities. The coordi¬ 
nation with Division 8 was at all times very close; in 
fact, three of the contracts of Division 2, namely those 
with Cornell University (under J. G-. Kirkwood), the 
Stanolind Oil and Gas Company (under Daniel Silver- 
man), and the Woods Hole Oceanographic Institution, 
were originally assigned to Division 8. Divisions 2 and 
11 and the Applied Mathematics Panel cooperated on 
various bombing problems, especially those dealing 
with the relative effectiveness of high-explosive and 
incendiary bombs. The contacts with Division 17 


were concerned chiefly with the problem of neutraliz¬ 
ing land mines; those with Division 18 were related 
to the properties of metals at high rates of strain. One 
contract, with the California Institute of Technology, 
was transferred from Division 2 to Division 18. 

The technical material which is described in this 
volume is the work of many people, not all of whom 
were connected with Division 2 of National Defense 
Research Committee. The work of many British labo¬ 
ratories needs to be especially mentioned, since the 
British were particularly effective in the fields covered 
by Division 2. Also, our own Service laboratories contrib¬ 
uted much to this type of work. Among the Division 2 
contracts, the largest were the Princeton University 
Station, directed by Walter Bleakney, and the Under¬ 
water Explosives Research Laboratory at Woods Hole, 
under Paul C. Cross. The Duke University contract, 
under Paul M. Gross, deserves special mention also, 
because of the successful development of the frangible 
projectile for gunnery training. 

The preparation of this volume has been a coopera¬ 
tive effort by a group of men, all of whom were directly 
engaged during the war on the projects about which 
they have written. To these authors, R. A. Beth, P. W. 
Bridgman, P. C. Cross, C. W. Curtis, P. M. Gross, 
W. D. Kennedy, C. W. Lampson, A. E. Puckett, E. M. 
Pugh, W. G. Schneider, J. J. Slade, Jr., R. J. Slutz, 
J. G. Stipe, Jr., and M. P. White, goes the credit for 
the high level of technical writing in the chapters 
which follow. The successful coordination of this 
joint operation is due to Merit P. White who has very 
ably edited the volume and organized the separate 
chapters into a coherent whole. 

E. Bright Wilson, Jr. 

Chief, Division 2 


COXFJltEXTIAli 


vii 
















PREFACE 


T his volume is not designed to be a detailed record 
of all work of Division 2. The time available for its 
preparation, no less than the type of reader for whom 
it is written, has prevented this. This report is de¬ 
signed for the use of individuals concerned with plan¬ 
ning or directing investigations similar to those de¬ 
scribed here, for whom a knowledge of the methods of 
attack, the difficulties that may be encountered, and 
the results that have been accomplished will be useful. 
Furthermore, an extensive, although not necessarily 
exhaustive, bibliography is included. For those desir¬ 
ing only an overall view of the work of this Division, 
and as an introduction for those planning to read the 
entire volume, a “Summary” has been prepared, com¬ 
prising Part I, immediately following the Table of 
Contents. 

The content of this volume comes partly from the 
fact that Division 2, throughout World War II, has 
been mostly concerned with information, and not with 
the development or improvement of devices. This in¬ 
formation has dealt with the performance of weapons 
and with defense against weapons. Some of it has been 
obtained by the Division through experimentation, 
some from tests by other organizations in NDRC, the 
Services, and among our Allies, and much information 
came from the field. Very early in the existence of 
Division 2 it was recognized that the value of any 
information obtained was a direct function of the use 
that was made of it, and that the potential users of 
this information were to a large extent organizations 
in the field. As a result, considerable thought was 
given to ways of getting information on weapon per¬ 
formance to such users in forms where it could and 


would be used. Because of the importance of these 
functions—getting, organizing, and dispensing infor¬ 
mation on weapons—not only in the existence of Divi¬ 
sion 2, but also to any other organization that under¬ 
takes the same problem, they are discussed in Part 
VII of this volume, “Liaison.” 

The research carried *out by Division 2 is treated 
under five categories, Parts II to VI of this volume. 
Part II is concerned with explosions in air, water, and 
underground. Muzzle blast control is included with 
these. Part III covers terminal ballistics of steel armor, 
concrete, plastic protection, and earth, and the develop¬ 
ment of a frangible bullet for training of aerial gun¬ 
ners. Part IV is concerned with rather fundamental 
investigations on the properties of matter, in par¬ 
ticular, the propagation of plasticity in solids, the 
behavior of steel under very large pressures, and the 
design of a supersonic wind tunnel. However, all re¬ 
search on supersonic problems done in the Division is 
discussed in Chapter 2 on explosions in air. Studies of 
protective measures are treated in the next part, Part 
V, except for those items that have been covered else¬ 
where in the volume Part VI is concerned with applica¬ 
tion of information on weapon behavior and effective¬ 
ness to the problems of selecting weapons for specific 
targets, and with estimating the resulting damage. 

Before concluding this already overlong preface, 
I wish to express my appreciation of the conscientious 
and painstaking efforts of my collaborators. 

Merit P. White 
Editor 


CONFIDENTIAL* 


ix 







CONTENTS 


CHAPTER PART I PAGE 

SUMMARY . 3 

PART II 
EXPLOSIONS 

1 Underwater Explosives and Explosions by W. G. Schneider, 

E. B. Wilson, Jr., and P. E. Cross .19 

2 Explosions and Explosives in Air by W. D. Kennedy .... 64 

3 Explosions in Earth by C. W. Lampson .110 

4 Muzzle Blast, Its Characteristics, Effects and Control by J. J. 

Slade, Jr .133 

PART III 

TERMINAL BALLISTICS 

5 Fundamentals of Terminal Ballistics by R. A. Beth .... 155 

6 Terminal Ballistics of Armor by C. W. Curtis .160 

7 Terminal Ballistics of Concrete by R. A. Beth .191 

8 Terminal Ballistics of Plastic Protection by J. G. Stipe, Jr. . . 229 

9 Terminal Ballistics of Soil by J. G. Stipe, Jr .233 

10 The Frangible Bullet for Use in Aerial Gunnery Training by 

P. E. Cross and M. P. White .242 

PART IV 

PROPERTIES OF MATTER 

11 Design of Model Supersonic Wind Tunnel by A. E. Puckett . . 251 

12 Behavior of Materials under Dynamic Loads by M. P. White . 255 

13 Deformation of Steel under High Pressure by P. W. Bridgman 

and M. P. White .266 

PART V 
PROTECTION 

14 Defense against Shaped Charges by E. M. Pugh .277 

15 Structural Protection by M. P. White .283 

CONF^DjamAL 1 xi 













Xll 


CONTENTS 


PART VI 


CHAPTER 


ATTACK 


16 Target Analysis and Weapon Selection by J. G. Stipe, Jr. 


PAGE 

305 


PART VII 
LIAISON 

17 The Division 2 Technical Library by R. J. Slutz 

18 Training of Operation Analysts by J. G. Stipe, Jr. 

19 Weapon Data Sheets by J. G. Stipe, Jr. 

Glossary. 

Symbols. 

Bibliography. 

OSRD Appointees. 

Contract Numbers. 

Project Numbers. 

Index . 


337 

339 

342 

473 

477 

479 

501 

502 

503 
505 


l O.NTipjiNTIAi. 


















PART I 


SUMMARY 


CONFLBEXTIAli 





























SUMMARY 


Chapter 1 

UNDERWATER 

EXPLOSIONS AND EXPLOSIVES 

T his chapter treats the physics and chemistry of 
underwater explosions. In Section 1.2 there is a 
survey of the results of investigations made on under¬ 
water explosions including the properties of the shock 
wave, the bubble oscillations, the surface phenomena, 
and comparison of explosives. 

The discussion of shock waves includes a treatment 
of the way in which they are produced, their shape, 
variation with weight and distance from charge, de¬ 
pendence on type of explosive, reflection from free, 
rigid, and deformable surfaces, and some numerical 
magnitudes which have been obtained. 

The treatment of the oscillation of the gas bubble 
covers the reasons for this oscillation, the dependence 
of the period of the oscillation on several variables, 
the migration of the gas bubble under gravity and 
under the influence of free and rigid surfaces, the 
pressure pulses radiated during the minima in this 
oscillation and their properties. 

Surface phenomena are described from the view¬ 
point of the theory of the domes and plumes above 
underwater explosions and the usefulness of these 
phenomena for various types of measurements. Under¬ 
water cratering is discussed briefly, as is the produc¬ 
tion of surface waves by underwater explosions. The 
results of the very extensive comparisons of different 
explosives for underwater effectiveness are summa¬ 
rized together with some remarks on the methods of 
statistical analyses used in connection with such com¬ 
parisons. The theories which were developed to cal¬ 
culate shock-wave properties, surface phenomena, 
surface waves, etc., are briefly reviewed. 

There is a section on damage produced by under¬ 
water explosions including some general considera¬ 
tions, the effect of target inertia, the effect of cavita¬ 
tion, diffraction effects, and the relation of shock-wave 
parameters to damage. Some theoretical and experi¬ 
mental investigations of several simple systems such 
as a steel diaphragm over an air cavity, the ball 
crusher gauge, and the simple crusher cylinder are 
discussed. The use of scaled models and the difficul¬ 
ties involved in their use are described. 

The section on experimental methods for studying 



underwater explosion phenomena contains a descrip¬ 
tion of a variety of underwater pressure gauges and 
their utilization, including both the electrical and 
mechanical types. Photographic procedures are de¬ 
scribed which were very fruitful in the study of 
underwater explosions. Experimental procedures are 
given for studying the generation of surface waves 
and for the location of underwater explosions (such as 
are useful in testing fuzes). 

The final section contains a description of the re¬ 
search facilities at the Underwater Explosives Re¬ 
search Laboratory [UERL] of Division 2, NDRC, 
which was located at Woods Hole, Massachusetts. 

Chapter 1 contains numerous references, the titles 
of which are contained in the bibliography. 


Chapter 2 

EXPLOSIVES AND EXPLOSIONS IN AIR 

This chapter deals with the behavior of shock waves 
in air; in particular, the air blast from high explosives 
is described, and the ways in which the air blast per¬ 
forms militarily useful functions are examined. 

During World War II, the techniques of measuring 
the highly transient phenomena associated with ex¬ 
plosions, theories concerned with them, and applica¬ 
tions of the information obtained were developed 
from very meager beginnings. The important role of 
blast in the functioning of bombs was truly appre¬ 
ciated only as the war progressed, and the develop¬ 
ment and use of very large blockbuster bombs was 
one consequence of this realization. 

Experimental methods for measuring and investi¬ 
gating the properties of blast waves in air are de¬ 
scribed in this report. Electrical gauges, mechanical 
gauges, methods depending upon measurement of 
shock-wave velocity, and photographic methods are 
discussed, and the advantages and disadvantages of 
each method are pointed out. 

The criteria for assessing the relative merits of 
weapons whose functioning depends upon air blast 
are based in part upon some observations of the blast 
damage accomplished by German bombs dropped on 
Great Britain, and British bombs on Germany, and 
in part upon semitheoretical studies of the response 
of structural elements to blast. For bombs that are 


3 







4 


SUMMARY 


not too large, the near-miss effectiveness is approxi¬ 
mately measured by the positive impulse in the blast. 
For very large bombs, and certainly for the atomic 
bomb, the peak pressure in the blast is considered the 
important factor. 

In an effort to improve the blast performance of 
high-explosive bombs, several high explosives were 
studied to determine their merits for this purpose. 
Results are usually expressed as the relative peak pres¬ 
sures and relative positive impulses from equal vol¬ 
umes of the explosives being compared. Compilations 
of such data from several sources were made, and the 
results are expressed as average relative peak pres¬ 
sures and relative positive impulses. These data dem¬ 
onstrate a marked superiority of aluminized explo¬ 
sives over nonaluminized explosives. Estimates of the 
relative areas of blast damage to be expected of several 
of these explosives were made, and are shown graph¬ 
ically in Figure 4. It is shown, for example, that a 
bomb filled with tritonal is estimated to produce about 
33 per cent more blast damage than would a similar 
bomb filled with TNT. 

The metal case of a bomb reduces the blast from 
its explosive contents. It is shown that the relatively 
thick case of a general-purpose [GP] bomb reduces 
the damaging power per ton of bombs by about 60 
per cent, compared with that obtainable from a light- 
case [LC] bomb. It is pointed out that the thinnest 
case consistent with safe handling and storage should 
be used for bombs intended to be detonated instanta¬ 
neously on impact or burst in air by means of a prox¬ 
imity fuze. 

The principle of similitude which permits the cal¬ 
culation of blast pressures, impulses, etc., from bombs 
of various sizes, from measurements with one size or 
weight, is stated, and its limitations discussed. The 
dependence of peak pressure and positive impulse on 
distance from the explosion are expressed graphically 
for bombs burst high above the ground, as well as for 
those on the ground. The advancement of theoretical 
work is described, and the extent to which it has been 
tested and checked by experimental results is outlined. 

By experimental and theoretical investigation of the 
properties of the blast from bombs burst at various 
heights above the ground as well as on impact, it is 
shown that there exists some optimum height of burst 
such that the area of damage of a desired category 
can be maximized, and that, on the average, the area 
of demolition as well as of less severe damage can be 
approximately doubled by use of air-burst, rather than 


ground-burst, fuzes. The experiments show, moreover, 
that the optimum height is not critical, and that 
both demolition and less severe damage can be nearly 
maximized by a single optimum height of burst for 
a given size of bomb. Estimates are made for the air 
burst of an atomic bomb for which the peak pressure 
is the criterion of damage, and it is estimated that, if 
the bomb were burst at the optimum height, the dam¬ 
age would be about 90 per cent greater than if it 
were burst on the ground. 

The relative effectiveness of explosives in enclosed 
spaces is quite different from that of explosives deton¬ 
ated in the open. It is shown that this difference is 
due to the relatively slow combustion of the products 
of the explosion, and that the order of merit of ex¬ 
plosives in enclosed spaces is the same as the order of 
their heats of combustion. The significance of these 
results is that small GP bombs whose near-miss effec¬ 
tiveness is almost nil should be filled with one of the 
explosives found to be best in enclosed spaces. The 
poorest explosive tested under these conditions is 
Composition B, and the best, tritonal. 

The history and present status of the development 
of slow-burning explosives [SBX] is described. Ex¬ 
perimental results show that certain SBX materials, 
such as one consisting of aluminum powder and gas¬ 
oline, dispersed and ignited by a high-explosive burst¬ 
ing charge, have promise of improved performance 
over high explosives as fillings of small (500- to 1,000- 
lb) bombs, whose main blast effect is obtained through 
direct hit and penetration of the target. 

The application of explosives to the clearance of 
land mines by blast is described. Demolition devices 
in the form of “line” charges were developed by the 
Engineer Board for this purpose. The measurement 
of blast pressures and impulses from some of these 
devices is described, and the results are shown graph¬ 
ically. A theory of the responses of the fuzes of land 
mines to the blast from explosive charges has been 
devised; by means of this theory, together with blast 
measurements, the distances at which mines should 
be cleared by various demolition charges have been 
calculated. Comparison of these predictions with ex¬ 
perimental observations of minefield clearance show 
good agreement for “point” charges, such as bombs, 
and poor agreement for line charges. More blast 
measurements and theoretical work are required in 
order to clear up these discrepancies. 

Blast measurements which were made at various 
altitudes up to about 14,000 ft above sea level show 


(ONLIDEXTIAL 





SUMMARY 


5 


that the order of merit among the explosives tested 
is unchanged, but that the magnitudes of the pressures 
and impulses measured are less at high altitudes than 
at sea level. Good agreement with theoretical predic¬ 
tions is obtained. 

The application of blast measurements to model- 
scale experiments with igloo-type storage magazines 
is described. The purpose of these tests was to assist 
in determining the minimum spacing between maga¬ 
zines, consistent with insuring that a disastrous chain 
of sympathetic detonations would not occur. Other 
measurements on the blast from rocket jets and from 
charges of various shapes are also briefly described. 

Chapter 3 

EXPLOSIONS IN EARTH 

Before the beginning of World War II, the ques¬ 
tion of the effects of underground explosions on 
nearby structures was not particularly important, be¬ 
cause the quantities of explosive involved were com¬ 
paratively small. The use of large and powerful bombs 
and the development of long-range bombers to deliver 
them anywhere in the enemy’s territory gave this 
problem immediate importance at the beginning of 
World War II. The existence of the atomic bomb and 
of various guided missiles for conveying it as well as 
conventional explosives to distant targets makes burial 
in the earth one of the most effective defenses for a 
future war. This means, in turn, that the effects of 
explosions in earth will be of even greater importance 
to both defense and attack than in the past. 

Because of the lack of reliable information on the 
nature and magnitudes of the phenomena that accom¬ 
pany an underground explosion, a very extensive series 
of tests was carried out cooperatively by the Corps of 
Engineers, the Committee on Passive Protection 
against Bombing, and Division 2, NDKC. These tests 
were made both in free earth and adjacent to buried 
reinforced concrete structures comparable to fortifica¬ 
tion construction, in a wide range of soil types from 
loess to saturated clay, and at scales up to 1,000-lb 
charges detonated adjacent to structures with 5- and 
10-ft walls. In free earth, transient measurements of 
pressures, accelerations, velocities, and earth movements 
were taken. Crater sizes and permanent displacements 
were determined after each test. With structures pres¬ 
ent, the same quantities were measured both on the 
structures and at distances from them. Structural 
damage was recorded and correlated with amount of 


explosive and its point of detonation with respect to 
the target. 

These data have been analyzed and the results ex¬ 
pressed by means of semiempirical equations and 
graphs. From these it is possible to predict, with an 
uncertainty of the order of 20 per cent, the pressures, 
impulses, accelerations, velocities, displacements, and 
crater sizes that will result from detonation of a given 
amount of explosive at a certain depth. In addition, the 
damage to structures comparable to those tested can 
be predicted with about the same order of accuracy. 

Chapter 4 

MUZZLE BLAST: ITS CHARACTERISTICS, 
EFFECTS, AND CONTROL 

Muzzle blast may be considered either as a rela¬ 
tively mild explosion following shot ejection or 
as an extremely high-pressure jet of short duration 
preceded by a traveling shock. The strength of this 
shock may be high, and depends on the muzzle pres¬ 
sure of the powder gas at the time of shot ejection. 
Within this spherical shock the gun empties in a jet 
characterized by a large bottle-shaped central region 
bounded by stationary shocks in which the gas attains 
very high speeds, and by an external turbulent shell 
in which the powder gases mix with the outside air. 
In this mixing region an explosive burning of certain 
components of the powder gas may occur, giving rise 
to the characteristic flash of medium and large caliber 
guns. The main emptying action occurs within a time 
comparable to the travel time of the projectile, al¬ 
though the low-pressure stages of the flow continue 
much longer. The main blast is followed by a wave 
of rarefaction which produces some flow of air to¬ 
ward the muzzle. 

With increasing powder pressures the severity of 
muzzle-blast effects becomes a limiting factor in the 
tactical use of guns of high muzzle velocity. The blast 
pressures often cause severe damage to structures near 
the muzzle and injuries and discomfort to personnel. 
Among the problems presented by muzzle blast is the 
raising of dust by guns firing at low elevations. In 
direct fire obscuration of the target is a serious handi¬ 
cap, since a gun is useless while it is enveloped in a 
cloud of dust. Unless powder pressures are to be lim¬ 
ited or high-pressure guns are to be replaced by weap¬ 
ons less damaging to the vicinity of the emplacement, 
it is necessary to develop devices that will lessen the 
effects of blast. 



6 


SUMMARY 


The most successful of the muzzle attachments so 
far developed is the muzzle brake. Brakes have been 
developed which absorb over 90 per cent of the recoil 
energy of guns, and there are indications that very 
high-pressure guns can be rendered practically re¬ 
coilless by means of such attachments. The reduction 
of recoil energy permits the use of light mounts with 
high-pressure guns. However, all brakes direct the 
blast intensity toward the rear of the gun, the back 
pressures produced rising with the efficiency of the 
unit; for this reason only brakes of moderate efficien¬ 
cies have been utilized. 

Since in most emplacements the elevation and 
traverse of a gun are limited, it is generally possible 
to design a muzzle attachment which deflects or de¬ 
forms the blast in such a way as to ensure a substan¬ 
tial amount of protection to neighboring structures. 
Also, such devices are usually brakes, but they can be 
designed so that the braking action is negligible. It 
is possible to deflect the blast unsymmetrically with¬ 
out affecting the flight or yaw of the projectile, but 
provision must be made to take up the eccentric thrust 
on the gun produced by such deflection. 

The slight upward deflection of the blast permitted 
by the strength of existing elevating mechanisms has 
been found moderately successful in solving the prob¬ 
lem of target obscuration produced by dust. With ele¬ 
vating mechanisms constructed to take the unsyrn- 
metrical thrust, it is conceivable that the dust problem 
can be satisfactorily solved. 

Brakes of low and medium efficiencies can be con¬ 
structed which suppress flash or, at least, do not ac¬ 
centuate it. It may be possible to go to high efficien¬ 
cies without enhancing flash. 

These partial solutions of the blast problem will be 
less successful as pressures increase. The conduction 
of the gases to the rear of the gun would permit effec¬ 
tive muffling of the blast, provided a sufficiently large 
fraction of the gas can be deflected through 180 de¬ 
grees. A deflector capable of doing this is still in the 
preliminary stages of development, but experiments 
so far indicate the feasibility of deflecting a substan¬ 
tial fraction of the blast and conducting it to where 
it can be ejected at relatively low pressure toward 
the rear of the gun or up over the carriage. Such a 
disposal system would permit the utilization of the 
maximum braking action, and the saving in weight 
of recoil mechanism and mount that this would make 
possible would compensate for the weight of the added 
superstructure. 


Chapter 5 

FUNDAMENTALS OF TERMINAL BALLISTICS 

Terminal ballistics, as distinguished from interior 
and exterior ballistics, deals with the interaction 
of the missile (bomb, projectile, etc.) and the 
target. While attention is usually focused on the effect 
of the missile on the target, resulting in penetration 
or perforation, the effect of the target on the missile 
causing deformation, rupture, shatter, fuze failure, 
etc., is often of great importance in determining 
the result of the missile-target interaction. 

Chapters 6, 7, 8, and 9 of this volume describe the 
terminal ballistics of steel, concrete, plastic protec¬ 
tion, and soil from the point of view of the work done 
on these subjects by Division 2 during World War II. 
Projectile deformation and shatter are especially 
significant in the study of steel and plastic protection 
targets. The development of a frangible projectile for 
aerial gunnery training, described in Chapter 10, de¬ 
pends on the complete shattering of the projectile at 
the target. 

A distinction is made between perforation and pene¬ 
tration according to whether the missile does or does 
not pass completely through the target. This distinc¬ 
tion applies particularly in the case of nondeforming 
missiles. The depth of penetration or the residual 
velocity after perforation depends not only on the ma¬ 
terial and thickness of the target, and on the mass, cal¬ 
iber, and shape of the projectile, but also on the im¬ 
pact conditions: striking velocity, yaw, and obliquity. 

Chapter 6 

TERMINAL BALLISTICS OF ARMOR 

To serve as a basis for the development of better 
armor-piercing projectiles, studies have been carried 
out to determine how the energy required for per¬ 
foration of a steel plate depends on mass, size, shape, 
and mechanical strength of the projectile components 
as well as the hardness, thickness, and obliquity of 
the target. Changes in these parameters were con¬ 
sidered both as they alter the energy required for 
perforation directly when the projectile stays intact 
during the impact and indirectly as they control the 
extent of projectile deformation. Deformations play 
a particularly important role when the striking veloc¬ 
ity is above 3,000 fps, that is, at hypervelocities. Al¬ 
though the practicality of projectile velocities in this 


i ONKITVFVmf. 





SUMMARY 


7 


range lias been well demonstrated, the difficulties in 
designing a nondeforming projectile still remain one 
of the principal obstacles to full attainment of the 
potential benefits of hypervelocity weapons. 

Aside from a description of new techniques that 
have been developed for terminal ballistic studies 
(Section 6.3), the principal points discussed in Chap¬ 
ter 6, which includes reference not only to work done 
by Division 2, NDRC, but to investigations of other 
organizations as well, are the following: 

Nondeforming Projectile—Energy Required 
for Perforation (Section 6.5) 

1. For nondeforming projectiles of a given shape, 
for a particular type of armor and for a specified 
angle of incidence, the “specific limit energy,” WV 2 t /d 3 , 
depends to a good first approximation only on the 
plate thickness expressed in calibers. Thus 



where W = projectile weight (lb), 

Yi = minimum velocity to perforate plate 

(fps), 

d — diameter or caliber of projectile (ft), 
t = plate thickness (ft), 

6 = angle of incidence, 

C = constant for plates of a particular 
hardness, 

-701 = general function of --and 0. 

d’J d 

The advantage of this form is that it reduces the 
performance of projectiles of all sizes to a common 
basis. 

2 . The form of f(t/d,0) depends on the mechanism 
of plate failure. Different mechanisms are discussed, 
but it is pointed out that there is no physical theory 
capable of predicting the exact form for plates of all 
thicknesses. A review is given of the empirical expres¬ 
sions for f(t/d,6) now in common use. 

3. In addition to plate thickness, the specific limit 
energy depends on plate hardness, there being an 
optimum value which results in maximum resistance 
to perforation. A perforation formula is given which 
includes hardness. 

4. There is a slight “scale effect” in the sense that 
the specific limit energy for plates of a given caliber 
thickness decreases with increase in the size of the 
projectile. Although this contradicts the above equa¬ 


tion, the discrepancy is not great since the effect is 
small. 

5. Except for thin plate and large angles of attack, 
a perfectly nondeforming projectile requires less en¬ 
ergy for perforation than one that deforms. 

Projectile Deformations—Shatter 
(Sections 6.6.1 and 6.6.2) 

1 . A projectile deforms progressively with increase 
in striking velocity. At the shatter velocity, which is 
somewhat above the velocity where the initial failure 
takes place, projectile deformation usually leads to an 
abrupt increase in the energy required for perforation. 
The dependence of the shatter velocity on the proper¬ 
ties of the projectile, the plate, and on the angle of 
attack are discussed. 

2 . The effect of shatter in increasing the energy 
required for perforation is greatest at normal inci¬ 
dence (increase by as much as 100 per cent) but drops 
off with the angle of attack until at very large angles 
a shattered projectile may perforate with less energy 
than one that remains intact. The increase is signifi¬ 
cant, however, for angles at least as great as 45 degrees. 

3. It is pointed out that, because of the occurrence 
of shatter, projectiles are sometimes able to perforate 
a target when fired over long distances but fail at 
point-blank range. As a result, the effect of firing a 
projectile at a velocity above its shatter velocity is 
usually to increase its effectiveness at long range at 
the sacrifice of good performance near the muzzle; 
there is no overall gain. 

Projectile Parameters (Section 6.6.3) 

1 . Correct design of an armor-piercing projectile 
depends on a choice of the best values for its nose 
shape, length, density, strength of material, and, in 
the case of a subprojectile, its size. Section 6.6.3 con¬ 
siders how changes in each of these parameters affect 
(a) the striking energy, (b) the energy required for 
perforation when the projectile stays intact, and (c) 
the conditions under which deformation takes place. 

2 . Because of the greater density of tungsten car¬ 
bide, projectiles made from this material have both 
a greater striking energy and a higher shatter energy 
than similar steel projectiles. If perforating ability 
is the criterion of goodness, tungsten carbide is un¬ 
doubtedly a better projectile material than steel. 

3. Regardless of the adjustment of parameters, a 
monobloc projectile made from present-day materials 
will not remain undeformed under all conditions of 
impact likely to be encountered in combat. This is 


(CONFIDENTIAL 






8 


SUMMARY 


true for the attack of homogeneous as well as face- 
hardened plate. 

Prevention of Shatter by Use of Caps 
(Section 6.7) 

Although the addition of a cap is very effective in 
preventing deformation of both steel and tungsten 
carbide projectiles, it is a detriment to perforating 
ability when it is not needed to avoid shatter or when 
shatter does not increase the energy required for per¬ 
foration. Whether or not the cap is of benefit depends 
on the striking conditions. A general discussion of the 
comparative performance of monobloc and capped 
projectiles is contained in Section 6.7. Some protec¬ 
tion for the nose of the projectile is always necessary 
if the striking velocity is extremely high. 

Hypervelocity Projectiles (Section 6.4, 6.5, 6.8) 

1. Some of the advantages and disadvantages of 
different types of hypervelocity tungsten carbide 
cored projectiles are mentioned in Section 6.8. All 
have about the same terminal ballistic performance 
but differ in other respects. 

2. On considering the interior and exterior ballistic 
behavior of subcaliber projectiles, it is seen that the 
striking energy decreases with decrease in diameter; 
less energy is required to make a hole of small diam¬ 
eter. However, since the striking and limit energies 
do not decrease at the same rate, there is usually an 
optimum diameter for the subprojectile. 

3. Examples are given showing that tungsten car¬ 
bide cored projectiles can perforate significantly 
thicker armor than conventional full-caliber steel 
projectiles fired from the same gun. 

Future Studies (Section 6.9) 

1. As the power of guns is increased, better means 
must be found for keeping the projectile intact. Par¬ 
ticularly for oblique attack, the problem of finding 
the forces involved in the plate-projectile interaction 
has hardly been touched. Once these forces are known, 
it should be possible to deduce the dynamic stresses 
produced in the projectile during impact and to design 
rationally against the resulting deformations. 

2. More satisfactory methods should be devised for 
preventing decapping and breaking of projectiles by 
thin skirting plates. 

3. Special attention should be given to high-angle 
attack. At the end of World War IT, it was impossible 
with the best antitank guns and projectiles available 
to defeat the sloping plates on the front of German 
tanks except at very close range. 


Chapter 7 

TERMINAL BALLISTICS OF CONCRETE 

A large amount of experimental work was done 
on the terminal ballistics of concrete during the 
war at scales from caliber .30 to 16 in. and with rein¬ 
forced concrete targets from 3 in. to 23 ft thick. Pene¬ 
tration was studied as a function of striking velocity 
and obliquity, and the limit velocities for scabbing and 
perforation for various thicknesses and calibers de¬ 
termined. For a given projectile and target, penetra¬ 
tion increases less rapidly with striking velocity than 
does the striking kinetic energy. 

A scale effect was found for penetration in the sense 
that the penetration into a given target, in calibers, 
of similar projectiles at the same striking velocity 
increases with approximately the one-fifth power of 
the caliber. 

Extensive tests were made, at caliber .50 scale and 
smaller, of the effect of concrete properties on pene¬ 
tration resistance. Some tests were also made of the 
effect of nose shape and the effect of projectile mass 
on penetration, perforation, and scabbing. Empirical 
formulas have been devised for representing these 
results. 

In addition, experimental data were obtained on a 
number of other phenomena, including ricochet, stick¬ 
ing penetration, front and back craters, the effect of 
reinforcing, scab plates and meshes, layers and lami¬ 
nations, composite and spaced slabs, edge effects, the 
effect of explosions, and the effect of repeated fire. 

A theory of concrete penetration was devised which 
agrees satisfactorily with the empirical penetration 
formula mentioned above and which gives the force 
resisting the missile during penetration as a function 
of depth and remaining velocity. Estimates of this 
resisting force are of importance in connection with 
the problem of projectile and bomb deformation 
against concrete targets. The theory, furthermore, 
furnishes a basis for computing the time of penetra¬ 
tion for fuzing problems, and for computing the re¬ 
maining velocity at any depth which is needed in the 
analysis of composite targets. 

Preliminary development work has been done on 
an electromagnetic method for measuring projectile 
velocity as a function of time during penetration in 
a nonmagnetic and nonconducting target material like 
concrete. 

A summary is given of analytical theories of pene¬ 
tration and perforation. This summary includes, as 


CONFIDENTIAL 






SUMMARY 


9 


special cases, all the theories which have so far been 
proposed for describing penetration and perforation. 

Chapter 8 

TERMINAL BALLISTICS OF PLASTIC 
PROTECTION 

Plastic protection consists of a mixture of stone 
and a mastic binder backed by a thin plate of mild 
steel. It requires only a small amount of strategic 
material and has proved valuable as protection against 
small-arms tire and fragments. 

The protective merits of plastic protection cannot 
be measured in terms of a simple ballistic limit, as 
is done with armor, mild steel, and concrete. At low 
striking velocities a small fraction of the incident 
missiles perforate the material, and at high striking 
velocities a larger fraction of the striking missiles 
perforate. At all ordinary velocities there is a definite 
probability of perforation, and this probability in¬ 
creases slowly with increase in striking velocity. This 
behavior can best be interpreted by statistical means, 
and such interpretation requires a large number of 
tests for the results to be significant. 

The best present specifications of plastic protection 
require quartzite or flint gravel of fairly uniform size, 
at least three times the diameter of the missile to be 
stopped. This gravel is mixed with asphalt and a lime¬ 
stone filler, and the mixture is poured from a hot mix¬ 
ing oven into forms. The best proportions for the mix 
are approximately 60 per cent gravel, 10 per cent as¬ 
phalt, and 30 per cent limestone dust, by weight. A 
backing plate of mild steel, having a weight per square 
foot of 10 to 30 per cent of the weight of the com¬ 
pleted panel, is securely fastened to the material. A 
layer of expanded metal is placed inside and near the 
front to aid in holding the material in place and to 
provide additional structural strength. A panel of this 
type, of thickness nine to ten times the diameter of 
the incident missile, provides a fair degree of protec¬ 
tion. 

Chapter 9 

TERMINAL BALLISTICS OF SOIL 

Small-scale experiments have been performed to 
determine the effects of soil properties and pro¬ 
jectile characteristics, especially nose shape and den¬ 
sity, on penetration into soil over a wide range of strik¬ 
ing velocities. The results of these small-scale tests 
have been correlated with the observed penetration 
of bombs and large projectiles into soil. 


It is found that penetration increases with increase 
in velocity and for projectiles and bombs of normal 
shape is approximately proportional to the cube root 
of the weight of the missile. Penetration depth is also 
dependent on the nose shape of the projectile, blunt- 
nosed projectiles penetrating farther than sharp-nosed 
projectiles. This dependence on shape is very pro¬ 
nounced in rich clay but small in coarse sand. Except 
for striking velocity and nature of the target medium, 
stability of the projectile is perhaps the most impor¬ 
tant single factor in soil penetration. Blunt-nosed pro¬ 
jectiles are usually stable and have long straight 
underground trajectories. Sharp-nosed projectiles usu¬ 
ally turn sideways and have curved underground 
trajectories. 

A summary of the known relations for penetration 
into soil, perforation of soil parapets by small-caliber 
bullets, and perforation of composite targets of con¬ 
crete covered with earth is given in Weapon Data 
Sheets 2A*, 2A2a, and 2Cla, Chapter 19. 

Chapter 10 

THE FRANGIBLE BULLET FOR USE IN 
AERIAL GUNNERY TRAINING 

The need for a realistic training procedure for flex¬ 
ible aerial gunnery was recognized in the late 
months of 1943. The development of a frangible bul¬ 
let which can be fired from machine guns in a bomber 
at an attacking lightly armored target airplane ful¬ 
filled the requirements to a marked degree. This proj¬ 
ect was concerned with the development of the fran¬ 
gible bullet (T44) and associated equipment, and with 
some problems that arose in connection with the use 
of the procedure in a gunnery training program. 

Experimental work with approximately one hun¬ 
dred types of bullets varying in composition, geome¬ 
try, and density indicated that a thermosetting plastic 
with dense filler offered the best possibilities for a bul¬ 
let that would (1) do minimum damage to the armor, 
(2) satisfactorily withstand field use and the loading 
process, (3) have reasonable flight characteristics, and 
(4) be amenable to relatively simple and economical 
production in the required quantity. For a particular 
thickness of armor, it appears that, to a fair approxi¬ 
mation, the limit impact energy of such bullets is es¬ 
sentially constant regardless of mass or density. 

The most suitable armor for the target airplane was 
found to be 24ST Dural in places where visibility was 
not in question, and multiplate bullet-resistant glass 
for locations where visibility was necessary. Up to 



10 


SUMMARY 


thicknesses of approximately 0.350 in., 24ST Dural is 
superior to armor steel, weight for weight, in defeat¬ 
ing the frangible bullet. 

A caliber .30 aircraft machine gun modified by ad¬ 
dition of a piston booster was found to function quite 
satisfactorily as an automatic weapon firing the fran¬ 
gible bullet of weight 6.95 g at a muzzle velocity of 
1,360 fps. The most satisfactory propellant found for 
the round with low loading density is DuPont SR4759 
which is regarded as a compromise until a more suit¬ 
able propellant can be obtained or the cartridge case 
changed to something other than the caliber .30 M-l 
case. 

A hit-indicator system was found to be quite effec¬ 
tive in signaling to the gunner in the bomber when the 
target airplane is receiving hits. The signaling is ef¬ 
fected by lights on the target airplane, which are acti¬ 
vated by the impacts of the bullets on the target-air¬ 
plane armor. 

The most essential feature of the introduction of 
the frangible bullet into a training program is the re¬ 
quirement that, to a fair approximation, the gunner 
give to the best of his knowledge the same leads as he 
would give in combat for an equivalent situation. It 
was found that the solution to the problem lay in an 
appropriate scaling of airplane and bullet velocities 
with some changes in the gunner's sighting device. 
Calculations of the combat leads, using the velocities 
of combat airplanes and combat ammunition, and of 
the training leads, using training airplane and bullet 
velocities, showed that for the most important cases 
the lead angles are essentially constant for equivalent 
situations. 

Field trials of the frangible-bullet technique have 
shown that it is a satisfactory procedure although def¬ 
initely not free from significant limitations. It was 
found that an instructor's sight would be a material 
aid in the training program and such a device was 
developed. 

Investigation of some of the psychological factors 
in sighting indicated that learning was comparatively 
rapid on a semisynthetic training device. There re¬ 
mains a real question as to whether such learning can 
he translated into a higher proficiency under condi¬ 
tions of air-to-air firing. 

Some experimental work by the Ballistics Research 
Laboratory [BRL] of Princeton University Station 
of Division 2 on shapes of bullets other than that used 
in the present T44 round has indicated that a bullet 
with a secant ogive and boattail has less drag below 
1,200 fps than does the T44 bullet. Preliminary in¬ 


vestigations by this same group have shown that a 
caliber .50 frangible slug made from material of the 
same density as the T44 is inferior to the caliber .30 
T44 in so far as velocity limit for perforation is con¬ 
cerned. 

Chapter 11 

DESIGN OF MODEL SUPERSONIC 
WIND TUNNEL 

In order to obtain information needed for the design 
of a large supersonic wind tunnel to be built at the 
Aberdeen Proving Ground, a model wind tunnel hav¬ 
ing a 2.5-in. square working section was constructed 
at the California Institute of Technology. This tunnel 
was designed to operate at Mach numbers from 1.2 to 
4.4. The specific problems that were solved are the 
following: 

1. The pressure ratios and power requirements at 
various Mach numbers. 

2. The design of nozzles to give supersonic flow in 
the working section. 

3. The manner of supporting the model to avoid in¬ 
terference with the air flow around it. 

4. Methods of observing the flow and of measuring 
the forces acting on the model. 

Chapter 12 

BEHAVIOR OF MATERIALS UNDER 
DYNAMIC LOADS 

Under very rapidly applied forces, such as occur 
during impact or explosion, a structure may be¬ 
have quite differently than under static or gradually 
applied forces. An investigation of these changes and 
of the factors governing them was one of the first prob¬ 
lems attacked by Division 2 in the course of its study 
of structural defense. The effect of dynamic loading 
is particularly important in connection with the pene¬ 
tration and perforation of projectiles, in the response 
of elements of structures to blast or impact, and in the 
damage to ship's plating by blast or underwater shock. 
In addition, there are numerous other situations where 
strength under impulsive loading is important, for 
example, in the calibration of crusher cylinders for 
measuring chamber pressures in guns. 

Two factors must be considered in any investigation 
of the effect of impulsive forces. First, there is a 
change in the physical characteristics of most mate¬ 
rials. As the rate of deformation is increased the re¬ 
sistance to deformation also increases. Thus for soft 


rOWFIBEXTIAT* 





SUMMARY 


11 


copper specimens the force required to produce a given 
deformation dynamically at a certain rate of straining 
was found to be of the order of 20 per cent greater 
than that required statically. Similar effects exist in 
steels. Furthermore, normally ductile materials are 
able to withstand stresses well above their elastic limits 
without permanent deformation if the forces are ap¬ 
plied for short enough periods. The investigation of 
the change in material properties under dynamic loads 
was pursued experimentally with some analytical as¬ 
sistance. 

The second important factor to consider in dynamic 
loading is the propagation effect. The effect of a force 
applied suddenly to a structure is not transmitted in¬ 
stantaneously throughout the structure, but with a 
finite velocity. Consequently, the more rapidly a force 
is applied the greater the tendency for the effect to be 
localized near the point of application. Thus a sudden 
tensile force on a wire tends to make it break at the 
loaded end. It is found that for instantaneously ap¬ 
plied forces the occurrence of localized failure depends 
on the velocity produced by the force, or, in cases 
where the loading is produced by impact, the velocity 
of impact is the governing factor. In general, there 
appears to be a definite critical velocity of impact for 
a given structure loaded in a given manner. Above 
this critical velocity failure occurs at the loaded point 
with very little deformation or damage in the rest of 
the system. Below the critical velocity failure may or 
may not occur at the point of application of the load 
(depending generally on the geometry of the system), 
but the damage and deformation to the structure will 
not generally be confined to the neighborhood of the 
load. Consequently, the amount of energy that can be 
absorbed by a structure under impact is usually very 
much less for velocities above the critical than for 
those below. 

The critical velocity of tensile impact for most duc¬ 
tile metals is of the order of 100 to 200 fps. In trans¬ 
verse impact on a thin member, such as a wire, the 
critical velocity is of the order of 300 to 600 fps. This 
effect may be important in the case of balloon mooring 
cables struck by planes, or for thin plates or dia¬ 
phragms under blast loads. 

Chapter 13 

DEFORMATION OF STEEL UNDER 
HIGH PRESSURE 

This investigation was a portion of the fundamen¬ 
tal research program undertaken by Division 2 and 


directed at acquiring an understanding of the mecha¬ 
nism of armor penetration by projectiles. During such 
penetration the material adjacent to the projectile is 
subjected to stresses of the order of 500,000 psi and 
to exceedingly large deformations. Comparable stresses 
and deformations cannot be reproduced in such mate¬ 
rial by the normal methods of testing since rupture 
always intervenes. Consequently, such tests can fur¬ 
nish only estimates of the amount of strain-hardening 
and of the conditions that produce rupture during 
projectile penetration. However, under large hydro¬ 
static pressures, rupture can be delayed sufficiently to 
allow both aspects to be adequately covered. The prin¬ 
cipal object of this investigation was to use this means 
of securing this information. During the first stages 
of the work another object was also in view, to deter¬ 
mine whether or not the information acquired during 
tests under large hydrostatic pressure could be corre¬ 
lated directly with the ballistic performance of a mate¬ 
rial. 

The following conclusions are drawn: 

1. The region of high pressure in the neighborhood 
of a penetrating projectile is characterized by practi¬ 
cally infinite ductility. This ductility is the result of 
the pressure and does not require any elevation of 
temperature. 

2. This region of high pressure and high ductility 
surrounding a penetration is also a region of very se¬ 
vere strain-hardening. This hardening may be by a 
factor of two or three, depending on the type of steel. 
This factor appears to be smaller for steels of high 
normal strength; thus there is partial compensation. 

3. This investigation has not revealed any signifi¬ 
cant correlation of the behavior under pressure with 
ballistic behavior. It appears that, in general, ballistic 
behavior is closely associated with fairly obvious char¬ 
acteristics, such as inhomogeneity, brittleness, pres¬ 
ence of inclusions, etc., which can be investigated by 
standard methods. 

4. The relation between applied force and the re¬ 
sulting deformation of a test specimen is not much 
affected by superposition of a hydrostatic pressure. 
In fact, the load to produce a given strain must be 
increased by an amount of the order of only 5 per cent 
for pressures of the order of 150,000 psi. On the other 
hand, the superposition of hydrostatic pressure in¬ 
creases very greatly the amount of deformation that 
can be produced before rupture, permitting investiga¬ 
tion of regions not otherwise attainable. 

5. The orientation of a specimen with respect to 


CONFIDENTIAL 





12 


SUMMARY 


the direction of rolling of the original plate has some 
effect on its rupture strength, but no observable effect 
on the load required for a given deformation. 

6. The Brinell hardness of steel appears to be in¬ 
creased by about 5 per cent for an increase in hydro¬ 
static pressure of 150,000 psi. 

Chapter 14 

m 

DEFENSE AGAINST SHAPED CHARGES 

The problem of providing protection against 
shaped-charge weapons has been studied in con¬ 
siderable detail. In the course of this investigation, 
a number of fundamental experiments and much theo¬ 
retical work have been carried on simultaneously with 
the necessary engineering type of experiments. 

As a shaped-charge jet penetrates the front of a 
target, the pressure it produces is so great that the 
strength of most target materials is unimportant and 
the process is governed primarily by the target den¬ 
sities. Materials of low density provide the greatest 
protection for a given weight. Densities from 100 to 
150 lb per cu ft are practical. However, strength is 
desirable at the rear of a target to prevent the flow 
that tends to continue after the jet is used up. 

The protection of armored vehicles was the prob¬ 
lem considered to be the most important, because of 
the fact that light infantry weapons had been devel¬ 
oped by the enemy that were capable of perforating 
and setting on fire any tank. Two practical protection 
devices were developed. The first was a set of remov¬ 
able steel panels containing plastic armor consisting 
of a quartz gravel, pitch, and wood-flour mixture (den¬ 
sity, 125 lb per cu ft) designated HCR2. The second 
was a set of steel plates with hardened steel spikes 
welded onto them. 

The panels were made to cover the majority of the 
most vulnerable areas of any M4 tank. The maximum 
protection of this type that could be applied without 
interfering with the operation of the vehicle added 
11.7 tons. Construction was started on two sets of 
panels, one using homogeneous armor and the other 
using mild steel. In the mild-steel panels the front 
plates were backed by aluminum. It is estimated that 
because of its thicker basic armor and the smaller area 
needing protection, the M26 tank can be provided with 
equivalent protection by adding 7.1 tons. 

The spikes provide protection by impaling the liner 
of the shaped-charge weapon and thus spoiling its per¬ 
formance. Protection of this kind can be provided 


against existing weapons with 4.1 tons for the M4 and 
3.2 tons on the M26. 

Because demolition hollow charges were being used 
against concrete fortifications, the protection of these 
structures was studied. Since concrete follows the den¬ 
sity law and its density is low, it is a fairly good pro¬ 
tective material itself. It was found that the weight 
of concrete needed for protection could be reduced by 
each or all of the following devices: increasing the 
strength of the concrete, providing an air space be¬ 
tween two walls of concrete, using a steel scab plate 
on the back surface, and using a steel face plate on the 
front surface. The reduction in weight achieved with 
the first twx> devices is very small, but with the last 
two it is more significant. The scab plate also protects 
personnel against scabbing fragments from a wall per¬ 
forated by a shaped-charge jet. 

Chapter 15 

STRUCTURAL PROTECTION 

To study the principles of design and construction 
of defensive structures, both civil and military, 
was the original function of Division 2, and, although 
the chief concern of the division shifted from defense 
to attack as the war progressed, defense never became 
wholly unimportant. Much of the work that was done 
was of fundamental nature; most of this is discussed 
in the early chapters of this volume, especially those 
dealing with explosions, with terminal ballistics, and 
with the properties of matter. Under “Structural Pro¬ 
tection/’ Chapter 15, are considered the experimental 
studies of structural behavior that are not treated else¬ 
where in the volume, and the methods of analysis and 
design of structures that have been developed. 

Generally, the important problems of structural pro¬ 
tection are: (1) to determine what attack will just de¬ 
feat a structure (this is likewise the principal problem 
of attack) or how much damage to a structure will be 
caused by a certain attack, and (2) how the resistance 
of a structure to attack can be increased, or structures 
of increased resistance be constructed. The following 
experimental studies have been made (mostly dis¬ 
cussed in Chapter 15) : the effect of underground ex¬ 
plosions on massive buried concrete structures, the 
damage caused by external and by confined explosions 
(briefly), the effect of contact explosions on concrete, 
and the behavior of reinforced concrete beams under 
impact. On the analytical side, both the elastic and 
the plastic types of behavior of structures have been 





SUMMARY 


13 


studied and reasonably simple methods of predicting 
the effect of a given impact or impulse on a structure 
or structural element devised. Comparisons with ex¬ 
periment for cases of plastic behavior are shown in 
the appendix of this chapter. 

Impact or contact explosion generally causes both 
local and general damage. The local damage may con¬ 
sist of cratering on the side of the attack, scabbing 
on the far side, or even perforation of the target. Scab¬ 
bing may be a very serious danger to personnel or 
equipment within a fortification or shelter. Its likeli¬ 
hood can be reduced by the use of scab plates or scab 
mesh on the inside face that are well tied to the inte¬ 
rior of the wall. In the absence of such devices, the oc¬ 
currence of scabbing is determined by the quantity and 
strength of explosive, on whether or not it is backed 
by earth or other material, and by the strength and 
thickness of the wall. Expressions for the limiting wail 
thickness for a given amount of explosive with and 
without backing are given. Expressions are also given 
whereby the size of craters can be predicted in a given 
situation. 

General damage, distributed over the more distant 
parts of a target is caused by either contact or distant 
explosion, or by impact. The extent and distribution 
of the effect are determined by the characteristics of 
the structure and by the amount and distribution of 
the pressure exerted on the structure. When the dura¬ 
tion of this impulsive load is short the impulse, or 
area of the active force-time relation, determines the 
effect. Methods of predicting this effect are discussed 
and their agreement with experiment shown to be ade¬ 
quate. In addition, the magnitude of impulse associ¬ 
ated with a contact, air-backed explosion is shown to 
depend on the amount and kind of explosive, and on 
the shape of the explosive charge, the impulse being 
greater as the center of gravity of the charge is moved 
closer to the contact surface. An expression for pre¬ 
dicting the amount of the impulse is given. 

Chapter 16 

TARGET ANALYSIS AND WEAPON 
SELECTION 

The efficient prosecution of a war requires that 
weapons be selected for each target in such a way 
that the maximum damage results for a given expen¬ 
diture of effort. The proper weapon and the necessary 
weight of attack using this weapon can be determined 


by careful analysis of the target and by application 
of the principles of weapon selection. 

In bombing attacks, the physical damage to the tar¬ 
get is usually measured in terms of the area damaged 
to a specified degree, and the efficiency of a particular 
weapon against the target in question is expressed by 
its mean area of effectiveness [MAE]. This quantity 
is the average expected area of damage for one bomb, 
divided by the weight of one bomb. The greater the 
MAE, the more efficient the weapon against the given 
target. The MAE for a particular combination of 
bomb and target may be determined in several ways; 
the most reliable method is by measuring the damage 
occurring in a large number of bombing attacks in 
which targets of the particular type were damaged. 

Targets may be damaged by external air blast, con¬ 
fined blast, underground explosion, underwater explo¬ 
sion, fragmentation, debris, or fire. The target must 
usually be analyzed in terms of its vulnerability to 
several of these mechanisms, and that mechanism to 
which the target is most vulnerable selected. The weap¬ 
on capable of causing the desired type of damage, and 
having the greatest MAE for the target under con¬ 
sideration, is usually best. In some cases the greatest 
overall efficiency is obtained by selecting some bomb 
other than that having the highest MAE for the tar¬ 
get, since all bombs do not load to equal weights on 
aircraft. The bomb expected to cause the greatest 
damage per plane load can be determined from a 
knowledge of the MAE and the loading characteristics 
of each bomb under consideration, and should be se¬ 
lected for the greatest efficiency. 

In many instances of bombing attack a knowledge 
of the mechanism of damage to which the target is 
most vulnerable will determine the best type and fuz¬ 
ing of bomb and frequently will also determine the 
most efficient size of bomb to be used. For example, 
air blast is most efficient if very large light-cased 
bombs are used and are fuzed for air burst; confined 
blast requires GP (occasionally SAP) bombs with short 
delay fuzing; underground explosion requires GP 
bombs with delay fuzing; depth bombs are especially 
designed for causing damage by underwater explosion 
and should be used with properly set hydrostatic 
fuzes; specially designed fragmentation bombs, with 
instantaneous or air-burst fuzes, should be used for 
targets vulnerable to fragments; incendiary bombs 
are for use against combustible targets. 

A detailed discussion of the methods of applying 
a knowdedge of the mechanisms of damage and a 


COXFIDENTHt 







14 


SUMMARY 


knowledge of the characteristics of the target to weap¬ 
on selection and determination of force requirements 
is given in Chapter 16. These principles are applied 
to military targets, transportation targets, and indus¬ 
trial targets. The results of many of the target anal¬ 
yses given in this chapter are given in abstract form 
in Section 6 of the Weapon Data Sheets of Chapter 19. 

Chapter 17 

THE DIVISION 2 TECHNICAL LIBRARY 

Since the principal function of the division was 
the collection, analysis, and distribution of infor- 
mation on the performance of weapons, a library was 
essential to its existence. The organization of the li¬ 
brary was designed to tit into the organization and 
functioning of the division as closely as possible. Clas¬ 
sification of reports was by subject, with very com¬ 
plete cross referencing by subject (all the subjects 
touched on in each report were used), by author, by 
title, and by all reference numbers appearing on each 
report. This made it possible to locate a report of 
which only a fragmentary description was available; 
it was also possible to find all reports in the library 
that dealt with a particular subject. 

The usefulness of the library was considerably in¬ 
creased by the preparation of abstracts of all reports 

as thev were received. These abstracts were distributed 
«/ 

promptly to the various research workers in the divi¬ 
sion, enabling them to request those reports of partic¬ 
ular use to them, serving the purpose better than a 
simple acquisition list. The abstract of each report 
was also put on its principal subject filing card so that 
a subject search through the library was possible with¬ 
out an examination of all reports in the field in ques¬ 
tion, and was not handicapped by the absence of any 
reports that happened to be on loan. 

The reports received were obtained from various 
sources. British reports on weapons and weapon per¬ 
formance came through the OSRD Liaison Office. Re¬ 
ports prepared by the American Services were obtained 
through Group A of the Liaison Office. Those members 
or associates of the division who were attached to, or 
in contact with, other research or investigating or¬ 
ganizations were of great assistance in securing re¬ 
ports. By the end of World War II the contents of the 
library amounted to about 20,000 items. 

Perhaps the most important requirement for a suc¬ 


cessful library is that it receive the serious and prefer¬ 
ably the full-time attention of a capable individual 
and not, as tends to be the case, be given to the newest 
member of the organization as one of his minor re¬ 
sponsibilities. 

Chapter 18 

OPERATIONS ANALYSTS 

A training course for operations analysts, to act 
as consultants on weapon effectiveness and bomb 
selection, was given at the Princeton University Sta¬ 
tion of Division 2. The training program included 
lectures on the fundamentals of terminal ballistics 
and explosive effects, a review course in mechanics, 
and a special course in mathematical probability and 
its applications to bombing problems. Additional train¬ 
ing by other organizations included instruction on 
the characteristics and effects of incendiaries by 
NDRC Division 11, on rockets by NDRC Division 3, 
on bombs and fuzes by the U. S. Navy Bomb Dis¬ 
posal School, further training in mathematical prob¬ 
ability by the Applied Mathematics Panel, and a short 
course at the Army Air Forces School of Applied 
Tactics. 

Approximately forty men were trained. They were 
assigned to operations analysis sections of several 
Army Air Forces, the Joint Target Group (AC/AS 
Intelligence), various naval organizations, and to 
other work where a knowledge of weapon performance 
was required. 

The work of these men was very well received, and 
some of them were clearly influential in decisions taken 
at higher levels. Most of the men worked for the Army 
Air Forces, and all indications are that the Army Air 
Forces were well satisfied with their work in analyzing 
targets and determining their vulnerability. 

Chapter 19 

WEAPON DATA SHEETS 

Division 2 has prepared a loose-leaf notebook giv¬ 
ing, in compact and accessible form, quantitative 
information on the characteristics and performance 
of weapons. The emphasis has been on aerial bomb¬ 
ing, but other weapons are included. This notebook 
was issued in loose-leaf form so that new material and 
revisions of old material could be added at frequent 
intervals. 







SUMMARY 


15 


The notebook was first published in July 1943. 
Fifty copies containing 15 Weapon Data Sheets and 
6 Incident Summaries were issued then. The book 
finally included a total of 81 Weapon Data Sheets and 
IT Incident Summaries. The final distribution, includ¬ 
ing the desk-size loose-leaf notebook, a pocket edition 


for field use, and bound copies of the final edition, 
reached a total of nearly 1,200 copies. 

All sheets of the final edition, with one omission 
and a few minor corrections, are reprinted in Chapter 
19 to serve as reference material for the other chapters 
of this report. 


'confidential 











PART II 


EXPLOSIONS 




Chapter 1 

UNDERWATER EXPLOSIVES AND EXPLOSIONS 


11 INTRODUCTION 

U nderwater explosions are of obvious military im¬ 
portance in connection with attack upon merchant 
and naval vessels, including submarines, and in the 
clearance of underwater obstacles both artificial and 
natural. In addition, they have recently been used 
for long-distance signaling. In order to utilize such 
explosions most effectively and in order to design the 
most efficient underwater weapons and to develop 
quantitative methods for determining explosive effec¬ 
tiveness in various weapons, it is necessary to have 
an understanding of the physics and chemistry of 
the phenomena involved. a For these reasons it was 
decided by the National Defense Research Commit¬ 
tee [NDRC] that a laboratory for the investigation 
of underwater explosions should be set up. The Under¬ 
water Explosives Research Laboratory [UERL] was 
accordingly established, first under Division 8 (Ex¬ 
plosives), by means of a contract with the Woods Hole 
Oceanographic Institution at Woods Hole, Massachu¬ 
setts. In 1944, this contract was transferred to the 
jurisdiction of Division 2 (Effects of Impact and 
Explosion), as a consequence of reorganization of 
Division 2. 

Before the founding of the Underwater Explosives 
Research Laboratory, work had been done on under¬ 
water explosions by the Naval Ordnance Laboratory 
[NOL], the David Taylor Model Basin [DTMB], 
the Submarine Mine Depot, and by various organiza¬ 
tions in Great Britain. 1 The British work especially 
had clearly outlined the principal features of the 
phenomena to be studied and had, in addition, indi¬ 
cated some of the most promising directions for the 
development of instrumentation. In spite of this, 
however, the state of knowledge in 1941, when work 
was begun under NDRC, was extremely rudimentary. 

By the end of World War II, a large amount of 
information had been acquired, both by the British 
and by ourselves, concerning the nature of the explo¬ 
sion process, particularly as concerns the shock wave 
emitted by an underwater explosion. The relative effec¬ 
tiveness of various explosives had been measured. 
Furthermore, studies had been made, though not 

a Pertinent to War Department Projects OD-03 and 
OD-131 and to Navy Department Projects NO-138, NO-223, 
NO-224, NO-237, NO-263, and NS-267. 


completed, on the so-called bubble phenomena, that 
is to say, the pulses emitted by the oscillating gas 
globe resulting from an underwater explosion. Some 
work had been done on the theory and mechanism of 
damage to structures but this work was very far from 
being complete. 

12 SURVEY OF RESULTS OF UNDERWATER 
EXPLOSION INVESTIGATIONS 

The term “high explosive” is used for those sub¬ 
stances which are capable of undergoing an exceed¬ 
ingly rapid decomposition known as detonation. 2 This 
distinguishes a high explosive from propellants or 
“low” explosives which decompose by a process of 
rapid burning. In the detonation process, the reaction 
zone spreads through the material at a rate deter¬ 
mined by the physical laws of conservation of mass, 
momentum, and energy. In the burning process, the 
rates of the chemical reactions involved are not fast 
enough to sustain a “detonation front,” and hence the 
rate of conversion of reactants to products is limited 
by the rates of these chemical reactions. 

121 Description of a Typical Weapon 

A normal underwater weapon consists of a main 
charge of high explosive, for example, TNT, a booster 
charge, which is a small charge of a somewhat more 
sensitive explosive, and an initiator, which is a deto¬ 
nator cap containing a percussion or heat-sensitive 
explosive in very small quantity. The initiator or deto¬ 
nator cap is fired by the fuze mechanism. For example, 
in a depth charge this may be triggered by the hydro¬ 
static pressure which causes a striker to hit the deto¬ 
nator cap and thus set off the very sensitive material 
in it. This small explosion detonates the booster charge 
which, in many weapons, consists of a few pounds of 
powdered TNT. The resulting explosion is then suffi¬ 
ciently powerful to detonate the main charge of less 
sensitive material. The chemicals contained in the 
detonator are too sensitive to be handled in any quan¬ 
tity, so that only a few grains are used. Mercury ful¬ 
minate or lead azide are commonly used in detonator 
caps, often combined with a small quantity of tetryl. 
Either impact, as in concussion cap, or heat, as in an 


3C 0 XFI DENT I A!*', 


19 






20 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


electric cap, will cause these combinations to detonate, 
whereas cast TNT and other military explosives, suit¬ 
able for the main charge, should not detonate with a 
comparable excitation. 

122 Explosives Commonly Used for 
Underwater Weapons 

The materials which have been most commonly used 
for the main filling in underwater weapons are TNT, 
amatol, minol, torpex, and HBX, whose compositions 
are given in Table 1. (Tritonal and RDX-Composi- 


Table 1. Explosive compositions.* 


Component proportions! 

Explosive 

AN 

RDX 

TNT 

A1 CaCl 2 D-2 

Wax 

TNT 

.... 

.... 

100 

. 

.... 

Amatol 

40-80 

• • • • 

60-20 

• ••• •••• 

.... 

Minol-2 

40 

, , , , 

40 

20 . 

.... 

Torpex-2 

• • • • 

42 

40 

18 . 

0.7 

HBX-1 

• • • • 

40 

38 

17 +* 5 

• • • • 

Tritonal 

• • • • 

• • • • 

80 

20 . 

1 

RDX-Comp.-B .... 

60 

40 

.... .... .... 

.... 


AN ammonium nitrate 

RDX Cyclonite, cyelomethylene trinitramine 

TNT trinitrotoluene 

A1 aluminum metal, powdered 

CaCl 2 calcium chloride 

D-2 high-melting wax/nitrocellulose/lecithin = 84/14/2 
Wax a variety of high-melting waxes have been used. 

* For a summary of the properties of the more common explosives, see 
Data Sheet 1A1, Chapter 19. 

t Production lots of mixtures may vary by as much as 1% from the listed 
proportions. 

tion B are included, since they were extensively used 
by the air forces against land targets.) 

The introduction of aluminum into military explo¬ 
sives on a large scale was one of the outstanding de¬ 
velopments of World War II. This addition very 
greatly increases the energy released on detonation 
and therefore the effectiveness of the charge. No other 
change in chemical composition produces nearly so 
great an enhancement of the effect as the introduction 
of aluminum. 

Torpex was the most powerful military explosive 
used during World War II. IIBX is a form of torpex 
in which a desensitizer has been incorporated to make 
the material less hazardous to handle. 

A considerable number of other materials have, of 
course, been used, especially by enemy nations. 

123 The Detonation Process 

High explosives are chemical compounds contain¬ 
ing large amounts of energy; that is to say, com¬ 
pounds which can undergo reaction to a set of prod¬ 



ucts of considerably lower energy. This reaction in the 
ordinary type of high explosive does not require oxy¬ 
gen from the air but is a process which will go spon¬ 
taneously without outside assistance once it is started. 
Most high explosives are organic nitro compounds; 
that is, they have the N0 2 group attached to carbon 
atoms in a molecule. The attachment is by way of the 
nitrogen atom. During the explosion reaction, the 
atoms in the molecule are partially broken apart and 
rearranged so that the normal products would be 
water, carbon monoxide, carbon dioxide, and nitrogen. 
In other words, the oxygen transfers from the nitro¬ 
gen to hydrogen and carbon, to which it can be more 
strongly bound, thus releasing a very considerable 
quantity of energy. If aluminum is present, it has a 
strong attraction for the oxygen and, during the re¬ 
action, takes up all the oxygen needed from the other 
material. This process of decomposition and rear¬ 
rangement of the atoms is exceedingly rapid in an 
explosive but is not instantaneous. Furthermore, even 
if the reaction velocity were infinite, the laws of con¬ 
servation of matter, conservation of momentum, and 
conservation of energy would place a limit on the 
velocity with which the region of decomposition could 
proceed down a stick of explosive detonated at one 
end. This velocity in a solid high explosive is ex¬ 
tremely great, of the order of 10,000 to 20,000 fps 
but it can be, and has been, accurately measured. 
Detonation velocity is an important property and one 
which is now quite well understood. For most military 
applications, it is not a measure of the power or use¬ 
fulness of the explosive. Methods exist for calculating 
the detonation velocity of materials which have not 
been made in more than gram lots. What is required 
is the chemical formula of the material and the 
heat of combustion. These considerations of thermo¬ 
dynamics and hydrodynamics, namely, the conserva¬ 
tion laws of mass, momentum, and energy, permit a 
computation of the detonation velocity which agrees 
quite well with that measured experimentally. For a 
more complete discussion of the detonation process 
and studies on detonation velocity, the reader is refer¬ 
red to the Summary Technical Report of Division 8. 

As the detonation process proceeds down the stick 
of explosive, the solid explosive in front of the deto¬ 
nation wave is unaware of the existence of the explo¬ 
sion because the detonation wave is traveling with a 
velocity greater than the velocity of sound in the ex¬ 
plosive material. Behind the detonation front, the 
pressure rises almost instantly to an exceedingly high 
value of the order of 2,000,000 psi. 3,4 If the explo- 

•:xTi.\r* 










RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


21 


sive is unconfined, this region of high pressure will 
rapidly expand into the surrounding medium, whether 
air or water, and thus fall ultimately to atmospheric- 
pressure. If the explosive is contained in a metal case, 
the case is ruptured. 

Under certain conditions, a high-order detonation 
such as described above does not occur. For example, 
if the initiation process is inadequate, the explosive 
may simply burn if open to the oxygen of the air. 
This burning is very fierce but a very much slower 
process indeed than detonation. The energy released 
may be actually greater than in the case of detonation 
but it is released over a relatively long time and, 
therefore, does not have the shattering effects of a 
true explosion. Even in the absence of oxygen, the de¬ 
composition may take place at a lower velocity or may 
begin and then die out, leaving a large mass of un¬ 
reacted material. It is also possible that a fairly thin 
layer of material near the surface of the explosion 
may be blown away without decomposition. This layer 
would, therefore, not contribute its energy to the ex¬ 
plosion. These questions of so-called low-order deto¬ 
nations are not completely understood but can usually 
be avoided by having a suitable booster. 

As the detonation wave passes a given point in the 
explosive, there are left the gaseous products of the 
decomposition of the explosive at a very high pressure, 
moving with a considerable forward velocity. This 
pressure is sufficient to burst the container of the 
weapon without regard to the tensile strength of the 
metal; in other words, the metal has an effect on the 
situation only through its inertia, since its strength 
is utterly negligible compared with the forces which 
are acting upon it. In an underwater explosion, the 
thin containers normally used have very little influ¬ 
ence on either the internal or external phenomena, so 
far as is known. 

124 Properties of the Shock Wave 

The very high pressure in the explosion products is 
communicated to the water immediately surrounding 
the charge, since the gaseous products naturally begin 
to expand at once and, therefore, to push against the 
surrounding water. It is often stated that water is in¬ 
compressible but, of course, this is only a relative 
statement. Water is much less compressible than air 
but is considerably more compressible than, say, steel. 
Under the influence of the very great pressures pro¬ 
duced in an explosion, a thin layer of the water around 
the charge is highly compressed and accelerated out¬ 


ward. This compression and outward motion is then 
transmitted to the next layer of water, and so forth, so 
that a wave of compression spreads out through the 
water, accompanying which the water acquires an out¬ 
ward mass motion. 

Nature of the Shock Wave 

The compression wave has certain very interesting 
properties. In the first place, it has a very steep front; 
in other words, the rise in pressure as the wave 
reaches a given point is practically instantaneous. 
This is partly because the explosion which produced 
the pressure wave was a very rapid event in itself. 
Even if a slower process were used to start the pres¬ 
sure wave so that it would not initially be steep- 
fronted, it would gradually become steeper as it 
. traveled outward through the water, because the high- 
pressure portions of the wave travel faster than or 
“overtake” the preceding low-pressure portions. This 
overtaking effect follows from two consequences of 
the passage of the preceding low-pressure wave. First, 
the water behind the low-pressure wave is compressed 
and somewhat heated, and hence transmits compres¬ 
sion waves more rapidly than the water ahead of the 
low-pressure wave. Second, the water behind the low- 
pressure wave has acquired a mass motion forward so 
that the high-pressure portion is being propagated 
through a forward-moving medium. The high-pressure 
regions thus tend to catch up with the low-pressure 
regions and eventually to form a very steep front. 

The steep front (see Figure 1) of the shock wave 
is followed by a region of decaying pressure which is 
to be expected because, as the explosion gases expand 
they will rapidly fall in pressure. In fact, this fall of 



0 12 3 4 

TIME IN MILLISECONDS 


Figure 1. Oscillogram showing pressure-time curve 
recorded by piezoelectric gauge. 


Confidential J 





22 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


pressure with expansion is much more rapid than one 
might at first expect. If the gases formed by the ex¬ 
plosion acted like gases at ordinary temperatures and 
pressures, the pressure would decay somewhat more 
rapidly than the volume increased according to the 
ordinary laws of gases. If one considers the properties 
of a gas with a density of, say, 100 lb per cu ft cor¬ 
responding to a pressure of about 2,000,000 psi and a 
temperature of the order of 3000 C, one sees that 
these properties should deviate widely from those of 
a gas at 1 atmosphere pressure and room tempera¬ 
ture. In fact, a considerable part of the high pressure 
exhibited by gas of this density is due to deviations 
from the ideal gas laws caused by the finite volume 
occupied by the individual gas molecules themselves, 
a volume which is normally neglected in discussions 
of gases at ordinary pressure. Therefore, as the gas 
expands, this contribution to the pressure is very rap¬ 
idly lost and there is a very rapid decay of pressure 
with expansion. This decay of pressure in the explo¬ 
sion products shows up as a decay in the pressure 
behind the peak of the compressional wave traveling- 
out through the water. 

The compressional wave, when it has become steep- 
fronted, is called a shock wave and is responsible for 
at least a part, and probably a major part, of the dam¬ 
age caused to ships and structures by noncontact 
under water explosions. 

If measuring instruments are located at some dis¬ 
tance from an underwater explosion, nothing is ob¬ 
served at the actual time of the explosion except 
possibly a flash of light in some cases. At a finite time 
later, depending upon the distance from the charge, 
there is a sudden rise in pressure to a maximum value, 
which is called the peak pressure in the shock wave. 
After reaching the peak value, the pressure immedi¬ 
ately begins to decay. The decay with time, at a given 
distance, is roughly given by an exponential expres¬ 
sion of the form 

P t = P m e~ t! \ 

where P t is the pressure at time t and P m and 0 are 
constants, the peak pressure and time constant re¬ 
spectively, of the shock wave at the given distance. 
The rate of decay is commonly indicated by giving 
the value of 0 which corresponds to the time re¬ 
quired for the pressure to fall to 1/e of its original 
value, where e is the base of the natural logarithm 
or 2.718. 

Suitable instruments might al^o be used to detect 
the motion of the water. This would be zero until 


the shock wave arrived at the point, upon which the 
water would immediately acquire a forward velocity. 
This forward velocity would decay as the pressure 
decayed. Because of this motion, the water through 
which the shock wave is passing possesses an outward 
momentum or impulse. This can be measured by ob¬ 
taining the area under the pressure-time curve at a 
point and is one important characteristic of the shock 
wave. Another obviously important characteristic of 
the shock wave is the amount of energy which is 
propagated outward past any given point. To a fair 
degree of approximation, this is given by the area 
under the curve in which the square of the pressure 
is plotted against time, though more accurate expres¬ 
sions can be given. If the pressure were low, such as 
is the case with ordinary sound waves, the integral of 
the square of the pressure gives accurately the energy 
transported. The forward velocity of the water is 
proportional to the pressure and, therefore, the kinetic 
energy of the water is proportional to the square of 
the pressure. 

Decay of the Shock Wave with Distance 

If the explosive is in the form of a sphere or of a 
cylinder not too far different from a sphere in shape, 
the shock wave will spread out more or less uniformly 
in all directions, thus forming what is called a spher¬ 
ical wave. (See Figures 2 and 3.) The area covered 



Figure 2. Flash photograph of f^-lb spherical pentolite 
charge detonated at center. 


■ 

TOXFIDKXTIAg 













RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 



Figure 3. Flash photograph of 1 2 -lb symmetrical cast 
pentolite cylinder detonated at center. 


by the wave will, therefore, increase as the square of 
the distance. Hence as the wave spreads outward from 
the source, it will decay and, if there were no dissipa¬ 
tion, that is, no conversion of energy into heat with 
the passage of the wave, the total energy would re¬ 
main constant over the whole spherical surface. Be¬ 
cause of the increase in area of the sphere, however, 
the energy transported across the unit area would 
decrease as the square of the distance from the ex¬ 
plosion. Connected with this would be a decay in the 
peak pressure which would follow an inverse first 
power law, since the energy, which is related to the 
square of the pressure, decays as the second power. 
The impulse or momentum would decay approximate¬ 
ly as the first power since it is the area under the 
pressure-time curve. In actual fact, there is some 
dissipation, since the passage of the shock front will 
result in an irreversible transfer of mechanical energy 
into heat through the action of viscous forces, etc. This 
loss of available energy causes the decay of the energy 
transport to he somewhat more rapid than the inverse 
square of the distance, though the effect is not very 
great. Consequently, the decay of the peak pressure will 
be somewhat greater than the inverse first power. 

The duration of the wave increases as the shock 


23 


progresses outward because the high pressure in the 
front of the wave travels faster than the low pressure 
in the “tail” of the wave. The increase in the dura¬ 
tion partly compensates for the extra decay of peak 
pressure with distance, thus bringing about the result 
that the impulse decays very nearly as the first power 
even when dissipation is considered. 

Order of Magnitude of Shock-Wave Parameters 
Some numerical values of the various shock-wave 
parameters discussed above are presented in Table 2. 

Table 2. Shock-wave parameters for 300 lb of 
cast TNT (density 1.52). 


Distance from charge (ft) 



20 

30 

60 

100 

Peak pressure (psi) 

6,150 

3,900 

1,820 

1,030 

Impulse* (psi-sec) 

3.68 

2.56 

1.41 

0.90 

Energy flux* (psi-in.) 

1,676 

750 

181 

64 

Time constant (msec) 

0.45 

0.50 

0.57 

0.61 


* Measured to a time behind the shock front equal to 6.7 times the time 
constant. 


The Low-Pressure Tail of the Shock Wave 

At a time behind the shock front corresponding to 
five times the time constant, the pressure has fallen 
to 5 or 10 per cent of the peak value and thereafter 
decreases very slowly. This low-pressure region is 
commonly called the tail of the shock wave. 5 On theo¬ 
retical grounds it is predicted that the pressure must 
eventually fall to zero and then go slightly negative, 
but at what time after the shock front this occurs 
is not definitely known. 

To date, accurate measurements of the tail of the 
shock wave have not been made. This is due to the 
fact that the instrumentation was generally designed 
to measure the higher pressures in the early part of 
the shock wave and thus the necessary accuracy for 
measuring the very low pressures in the tail was not 
realized. For explosive comparison measurements this 
difficulty was overcome by measuring the impulse 
and energy flux to some arbitrary time after the shock 
front. It was convenient for this purpose to choose a 
time equal to some multiple of 0, the time constant. 
For example, at a time after the shock front equal to 
8 6, the pressure has fallen to approximately 5 per 
cent or less of the peak value. It should be pointed 
out, however, that, although the pressure in the tail 
of the shock wave is very low, if it lasts long enough 
there may be a considerable quantity of momentum 
in this portion of the wave. Whether or not this 
momentum, which is delivered at a low pressure, is 
important in damage is not known. 


CONKlDK-NiTIAL. 

























24 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


The Principle of Similitude 

It is very fortunate that the peak pressure, dura¬ 
tion, and other properties of the shock wave from 
charges of one size can be very simply related to the 
properties of the shock wave from a charge of a dif¬ 
ferent size. The relation can be stated as follows: 

If every linear dimension of an explosive charge is 
multiplied by the same factor k, then at a distance 
Bk from the larger charge, the peak pressures will 
be identical to the value at a distance R from the 
smaller charge, but the duration, the impulse, and 
the energy from the larger charge will be k times 
greater at these related distances. If two charges have 
approximately the same shape and one is k times 
larger in its linear dimensions than the other, its 
weight will, of course, be k cubed times greater. The 
law can, therefore, be approximately stated by using 
the cube root of the weight ratio as the scaling factor 
k. As an example, one might compare the shock wave 
from a 300-lb TNT charge with the shock wave from 
a charge weighing %o of a lb and having the same 
shape as the large charge. The scaling factor is then 
10, the cube root of the weight ratio of 1,000. Conse¬ 
quently, one should expect to obtain the same pressure, 
about 6,000 psi, at a distance of 2 ft from the small 
charge as was obtained at 20 ft from the large charge. 
The duration, impulse, and energy at 20 ft from the 
large charge will each be ten times as great as the cor¬ 
responding quantity 2 ft from the small charge. It is 
very important to note that this scaling law, by itself, 
does not tell anything whatsoever about the law of 
decay with distance. No matter what the latter law 
should be, this so-called similarity or scaling law 
would be expected to hold. What it does do is con¬ 
nect the law which governs the way in which the 
shock-wave properties change with distance with the 
law for the change of shock-wave properties with 
charge size. It is, of course, assumed that when the 
charge sizes change, the explosive type, density, etc., 
are kept the same. Mathematically stated, the simi¬ 
larity law is: 

Pressure P = f 1 



Momentum 






Energy flux E = 1W/ 3 
Time constant 6 = lW/ 4 








where IT is the weight of the charge, R the distance 
from the explosion, and the f s unspecified functions. 
In actual fact, it is found both empirically and theo¬ 
retically that the decay of peak pressure with distance 
in water does not deviate greatly from the inverse 
first power as mentioned above. If the decay were 
exactly inverse first power, the similarity law would 
lead to the conclusion that the peak pressure at a 
fixed distance would increase as the cube root of the 
charge weight. The dependence on distance of the 
shock-wave parameters must be determined experi¬ 
mental^, and equations expressing their dependence 
are approximate, but the similarity law is presumably 
very nearly exact. 0,7 Figure 4 illustrates the accuracy 
with which similarity scaling represents the features 
of the pressure-time relation for spherical pentolite 
charges of from 4 to 80 lb. The deviations in the tail 
of the curve are probably experimental error, since 
measurements in this region are as yet subject to error. 

When targets or gauges, etc., are introduced into 
the picture, perfect scaling cannot be expected unless 
these objects are also scaled. That is to say, each of 
their linear dimensions should be multiplied by the 
scaling factor k. This extension of the similarity 
principle to targets as well as to shock-wave properties 
is called the Hopkinson rule and is subject to more 
uncertainty theoretically and experimentally than is 
the simple scaling law of the explosive charge and its 
shock wave. (See Section 1.3.3.) 

125 Interactions of Shock Waves 

with Surfaces 

Reflection at Free Surfaces 

The effects of the free water surface on the explo¬ 
sion have been neglected so far. When a shock wave 
reaches a free surface it is reflected, not as a wave of 
compression but as a wave of reduced pressure or rare¬ 
faction. This is a familiar phenomenon with sound 
waves and holds true also for high-amplitude shock 
waves. The surface of the water is thrown upward 
with less resistance than is water deeper in the ocean. 
Consequently, there is propagated downward the 
rarefaction wave mentioned above. If the target or 
gauge is beneath the surface at some distance from 
the explosion, it will receive not only the direct wave 
from the source, but also a wave which has been re¬ 
flected from the surface of the ocean and is therefore 
a rarefaction wave. The reflected wave will arrive at 
a somewhat later time than the direct wave because 
of the longer path. When it does arrive, being a wave 


Confidential 









RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


25 



t/W 3 IN MSEC/LB 3 


Figure 4. Similarity comparison of pressure-time curves for spherical cast pentolite charges of 4 lb and 80 lb. 


of rarefaction, it will tend to cancel the pressure still 
being exerted by the tail of the original wave. A 
pressure-time curve showing this reflection is given 
in Figure 5. This is the phenomenon of “cutoff” and 
can be the limiting factor in the range of effective¬ 
ness of charges in shallow water. The time interval 
between the compression and rarefaction and, there¬ 
fore, the resulting duration of the pressure pulse in 
shallow water can be at least approximately computed 
by using the known velocities of these waves and the 
geometrical direct and reflection paths. An approxi¬ 
mate formula for the cutoff time, t, which applies 



TIME IN MILLISEC 

Figure 5. Reproduction of piezoelectric gauge pressure¬ 
time curve showing “cutoff” of pressure due to reflection 
at sea surface. 


when Ii, the horizontal component of the charge-to- 
gauge distance, is large relative to the depth, is 

2gD 
cR ’ 

where g and D are the gauge and charge depths and 
c is the velocity of sound. 

Cavitation 

There is another phenomenon of importance which 
complicates this surface reflection effect and that is 
the phenomenon of cavitation. The reflected wave 
from the surface is a rarefaction wave, but water will 
not withstand any appreciable tension. Although it is 
claimed that extremely pure water under laboratory 
conditions can support at least several hundred 
pounds per square inch of tension, the evidence seems 
extremely strong that ordinary sea water, which 
would normally contain many impurities, including 
air bubbles, etc., can sustain practically no tension. 
When tension is applied, what happens is that the 
water is torn apart and small bubbles appear which 
contain either air or water vapor. These bubbles have 
been photographed, as illustrated in Figure 6. The 
occurrence of cavitation therefore limits the amount of 
rarefaction which can be transmitted through the 
water. This limit is approximately equal to the total 
pressure (atmospheric plus hydrostatic plus shock 
wave) which is present. Any greater rarefaction, 
which would tend to cause actual tension in the water, 
results in cavitation. 


i'OKFIDENTIAI^ 





















26 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 



Figure G. Flash photograph of shock wave reflected 
at free surface of sea. 

Reflection at Rigid Surfaces 

When a shock wave impinges upon a rigid surface, 
it is reflected as a compressional wave. In other words, 
it is more or less completely reflected without great 
change in shape. If the incident wave strikes the wall 
head-on, it will be reflected back along the same line, 
with the result that the pressure immediately in front 
of the wall at the time of reflection will be the sum 
of the incident and reflected pressures. To a consider¬ 
able degree of accuracy the peak pressure at the rigid 
reflecting surface will be twice the peak pressure of 
the incident wave in free water and the duration will 



Figure 7. Flash photograph showing advance of shock 
wave around cylindrical steel block. 


be approximately that of the free wave, provided the 
surface is of infinite extent or at least so large that 
signals coming from the edges do not arrive during 
the times of interest. 

The flash photograph of Figure 7 shows the re¬ 
flected shock wave in front of a steel block as well 
as the initial shock front. 

Macii Reflection 

If the wave strikes at an angle, the phenomenon is 
similar to the acoustic case of the reflection of a sound 
wave, provided the intensity is not too great. For each 



Figure S. Plot showing theoretical prediction of con¬ 
ditions under which Mach reflection will occur. 


angle there is, however, a theoretical lower limit to 
the pressure, above which simple acoustic-type reflec¬ 
tion cannot occur. 8 What does occur instead is the so- 
called Mach effect. Theoretical studies have been 
made 9,10,11 of the phenomena which take place under 


t ' I |:'i N I i.\ I J 





































RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


27 



Figure 9. Flash photograph showing ordinary acoustic 
intersection of two shock waves. 


conditions such that acoustic reflection can no longer 
occur. Some of the results on shock pressures in water 
are presented in Figure 8, reproduced from a Bureau 
of Ordnance report. 12 Note that the more glaring 
the reflection, the lower the pressure which is required 
to cause the Mach effect. When a Mach reflection takes 
place, there is also an incident and a reflected wave 
but these do not reach the surface. Instead, there is 
a transition region containing a wave running parallel 
to the surface, called the Mach “stem,” which con¬ 
nects the junction of the incident and reflected waves 
with the surface. Figures 9 and 10 illustrate the dif¬ 
ference between regular and Mach intersection of two 
shock waves. 13 These cases are essentially equivalent 
to the reflection cases since the reflected shock wave 
can be thought of as a second shock wave having its 
origin at an “image” charge behind the rigid surface. 
Experimentally, in this instance it is easier to study 
intersections of two shock waves than it is to achieve 
an ideal rigid reflector. 

The pressure relations are not fully worked out 
theoretically for the Mach phenomenon, which is of 
more importance in air than in water (see Chapter 
2), but it is known that the net result may be to 
cause the pressure exerted on a surface to be higher 


when the wave strikes at an angle than when it 
approaches head-on. 14 

Multiple Charges 

The enhancement of certain parameters in the Mach 
intersection zone of the shock waves from multiple 
charges suggests that a given weight might be more 
effectively used under certain conditions if divided 
into several properly placed and initiated parts. 15,16 ** 1 
Clearly the meager data now available on this whole 
field should be supplemented. 

Interaction oe Shock Wave with a 
Deformable Target 

Although it cannot be said that a full exposition 
of the phenomenon occurring when a shock wave re¬ 
flects off either a free or a rigid surface is available, 
there is at least a considerable body of knowledge re¬ 
garding these two types of events. When one considers 
the effect of a shock wave on a yielding surface such 
as the hull of a ship, the situation is much less satis¬ 
factory. If the surface is reasonably stiff, then one 
might use the rigid surface treatment, which would 
yield a doubling of the pressure in front of the sur¬ 
face. As soon as the hull plating begins to move, there 
will be sent out into the water a rarefaction wave be¬ 
cause the moving hull will tend to pull the water with 
it. Because of the inertia of the metal, its motion may 
continue after the shock-wave pressure has fallen to 
a low value. The rarefaction wave sent out by the 



Figure 10. Flash photograph showing Mach inter¬ 
section of two shock waves. 


t'OVFTDEXTTAf 








28 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


moving plate will certainly reduce the applied pres¬ 
sure and may often cause it to become negative. This 
will be especially true for a light, thin plate. If the 
pressure does become negative, then cavitation will 
follow. The appearance of cavitation in front of a 
plate being damaged by an explosive wave has been 
photographically demonstrated (see Figure 11) and 



Figure 11. Flash photograph showing cavitation 

bubbles in front of thin air-backed diaphragm. 

will profoundly modify the course of events. It is suf¬ 
ficient to say here that the effects of shock waves on 
yielding surfaces are complicated and not thoroughly 
understood. 

1.2.6 Behavior of the Gas Bubble 

Oscillations of the Bubble 

The gas bubble formed by the products of the ex¬ 
plosion will continue to expand for a considerable 
period of time after the explosion. Thus, for a 300-lb 
depth charge at, say, 50-ft depth, this time may be 
about 0.35 sec. Consequently the water which formerly 
occupied this space is moving outward during this 
whole time interval and when the bubble has reached 
its maximum expansion, the total displacement of the 
water is very considerable. In the example quoted, the 
maximum radius of the bubble would be about 17 ft 
and this figure represents the maximum displacement 
of the water which was originally in contact with the 
charge. This displacement is very much greater indeed 
than the quite small displacement of the water caused 
by the passage of the shock wave itself. The division 
of the phenomenon into two parts, a shock wave and 
then the so-called after-flow or incompressive flow of 
the water, is an arbitrary but very convenient division. 
The phenomena in the shock wave itself are most 


closely related to acoustic theory, in which the com¬ 
pressibility of the water is the all-important factor. 
On the other hand, the flow of the water in the later 
stages is best treated by the approximation of incom¬ 
pressive flow. One simply regards this large mass of 
water as being pushed out by the expansion of the 
bubble. 

The inertia of this large mass of moving water 
causes the expansion to go past the point of equilib¬ 
rium so that the pressure within the gas globe falls 
far below the hydrostatic pressure at the given point, 
and the size of the gas globe increases to a maximum 
value considerably in excess of its equilibrium value 
at that depth. This overshooting phenomenon will re¬ 
sult in a subsequent contraction of the gas as the hy¬ 
drostatic pressure of the water brings the outward flow 
to rest and then reverses it. The water then flows into 
the cavity, compressing the residual gases and again 
the inertia of the process carries the bubble past its 
equilibrium radius, so that actually the gas bubble 
is compressed down to almost the size of the original 
charge, with a consequent building up of the gas 
pressure. This pressure increase eventually cushions 
the inflow, brings it to rest and then reverses the flow. 
The net result of this series of events is a pulsating 
phenomenon. The gas globe oscillates in size, becom¬ 
ing larger and smaller, with a period which is very 
considerably greater than the times involved in the 
shock-wave phenomena. For example, a 300-lb depth 
charge at 50 ft has a period of pulsation of approxi¬ 
mately 0.70 sec. It is not difficult to devise a simple 
theory which yields a reasonably accurate calculation 
of the period of the motion. 17,25 By a simple con¬ 
sideration of the law of conservation of energy, it is 
found that the period is governed by the following 
formula: 

T = KW 3 Z “I, 

where T is the period, W the charge weight, and Z 
the depth of the charge plus 33 ft. The term K is a 
constant characteristic of the explosive. 

At the first contraction of the gas globe, there is 
a sufficiently high pressure produced in the gas to 
send out another compression wave through the water. 
This compression wave differs from the initial shock 
wave in that the pressure-time curve is not steep- 
fronted but is more or less symmetrical with respect 
to time. 26,27 The peak involved is not nearly so high 
as in the initial shock wave being of the order of %o 
to /4o that value, but the duration of this pulse is 
rather greater, with the result that the impulse involved 


i i > N ! 1 ! 'K \TLVT| 













RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


29 


in the first of these bubble pulses is of the same order 
or even greater than that transmitted by the shock 
wave. 28,29 The successive bubble pulses become smaller 
and smaller so that there is little practical importance 
from a damage viewpoint in considering any beyond 
the first. The energy that is originally present in the 
outward flowing water, which is of the order of 50 
per cent of the chemical energy, is gradually converted 
into heat by the formation of vortices or radiated as 
compressional energy of the bubble pulses. The first 
bubble pulse may contain approximately 5 to 8 per 
cent of the original chemical energy. It is seen from 
the formula above for the period that this bubble pulse 
phenomenon is a function of the depth below the sur¬ 
face whereas the shock-wave phenomenon is not, ex¬ 
cept for the surface cutoff. The effect of the depth 
arises because the force which causes the bubble to 
cease its expansion and go into a contractual phase 
is the hydrostatic pressure of the water which, of 
course, increases with depth. 


Bubble Migration Due to Gravity and 
Effects of Surfaces 

The large cavity filled with the burnt gases is nat¬ 
urally influenced by gravity and, in general, will rise 
under this force. The phenomenon is more compli¬ 
cated, however, because there is an interaction between 
the upward motion due to gravity and the expansion 
and contraction. Hydrodynamic theory predicts and 
experiment verifies that the most rapid upward mo¬ 
tion takes place when the bubble is in its contractual 
phase. When the bubble is expanding, the upward 
motion is relatively slow, because of the large volume 
of water which must be displaced then. In the con¬ 
tracting phase, the accumulated momentum affects 
smaller and smaller masses of water so that the ver¬ 
tical velocity becomes very great. This rather com¬ 
plicated phenomenon has a number of important 
applications, as will be mentioned later. 

The motion of the bubble is affected not only by 
gravity but also by the presence of free or rigid sur¬ 
faces. 21,22 ' 30 ' 32 A free surface causes a net repulsion 
of the bubble which under certain favorable condi¬ 
tions may actually overcome the effect of gravity and 
drive the bubble downward. The depth at which the 
gravity rise is balanced by the free surface repulsion 
is known as the upper “rest” position and is realized 
only for small charges. A rigid surface, on the other 
hand, attracts the bubble, on the average, particu¬ 
larly so that the bottom may attract the bubble and 
under special cases may prevent the rise under grav¬ 


ity during the first few oscillations. Thus there will 
also exist a lower “rest” position. 

It is difficult to give a simple, physical description 
of the cause of the attraction by a rigid surface and 
the repulsion by a free surface, although the effect 
was first predicted theoretically. 17 Some indication of 
the mechanism of this effect may be gained by remem¬ 
bering that, as the bubble expands during its oscilla¬ 
tion, the water is pushed away and must flow some¬ 
where. If a rigid surface is nearby, the water is pre¬ 
vented from flowing in that direction, so that the 
bubble is first repelled, but as the bubble begins to 
contract the reverse process occurs and the bubble 
is attracted to the rigid surface because water cannot 
flow in from that side directly. This explanation does 
not, however, indicate why the attraction during the 
contraction phase is larger than the repulsion during 
the expanding phase. 18,19 This difference is related to 
the interaction between the oscillatory motion and the 
overall motion of the bubble similar to the case of the 
interaction between gravity and the radial oscillation. 
This interaction causes the displacement of the bubble 
to be much more rapid during the contracting phase. 

Damage Due to Bubble Phenomena 

It is of great importance to determine whether the 
bubble phenomena are important in causing damage. 
In this connection there are three separate factors 
which should be considered: (1) the pressure pulses 
radiated at each minimum of the gas globe, (2) the 
outward radial mass motion of the water accompany¬ 
ing the expansion of the gas globe, and (3) the up¬ 
ward mass motion of the water resulting from the 
migration of the gas globe. 

It has been demonstrated theoreticallv 17,21 that the 

t j 

pressure pulse radiated by the bubble at its minimum 
is greatest when the bubble migration is small. Ac¬ 
cording to this result, known as the principle of stabi¬ 
lization, underwater mines should be located at the 
rest position to obtain the maximum damage at the 
surface of the water from the bubble pressure pulse. 
Thus, for a 300-lb charge the mine should be moored 
approximately 14 ft above the sea bed. However, pre¬ 
liminary measurements with 300-lb TNT charges at 
this location 28 indicated the effect to be very much 
less than predicted. Evidence of damage due to the 
bubble pressure pulse has been provided by photo¬ 
graphs, taken with a high-speed motion picture 
camera, of a cylinder being damaged by a small 
charge. 33 Some of these photographs are reproduced 





30 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 





6.6 


12.5 


13.3 


15.0 


10.0 


15.8 

... .. ■ i 


5.0 


16.6 


Figure 12. Photographs showing cylindrical model being damaged by explosion at depth of 400 ft. Numbers under 
photographs are times in milliseconds. 


in Figure 12. It is to be noted that additional damage 
to the cylinder takes place shortly after the bubble 
reaches its minimum size. The bubble does not migrate 
perceptibly in these pictures because of the large 
hydrostatic pressure at the depth of the experiment. 
In general, however, where an explosion occurs under 
n target, because the gas bubble will migrate upward 
by as much as 15 ft (for 300 lb of TNT, at about 50-ft 
depth), the bubble pressure pulse originates at a point 
which is much nearer the target, and thus the damage 
due to the bubble pulse may be comparable to that 
caused by the shock wave. This effect has been demon¬ 
strated on a small scale 15 - 18 ’ 34 by experiments in 
which the damage to diaphragm gauges (see Section 
1.3.2) directly above a charge was several times 
greater than the damage to similar gauges at the same 
distance from the charge but to one side. 

Of considerable interest is an anomalously high 
pressure in the bubble pulse which has been observed 


at a depth of 20 ft for 300-lb TNT charges 28 and at 
a depth of 4 ft for Va-lb TNT charges. 29 Bubble pres¬ 
sures at these charge depths are at least five times as 
great as those at any other depths. The duration of 
this pressure pulse is relatively short, and the charge- 
depth range over which the phenomenon was observed 
was very narrow. No explanation for this behavior 
can be advanced at this time. It has been suggested 
that the bubble at these depths intersects the surface 
at its maximum expansion and sucks in air. On re¬ 
compression, a second chemical reaction may take 
place giving rise to additional energy. Further inves¬ 
tigation is needed. 

Mention was made of the mass motion of the water 
accelerated radially outward as the bubble expands. 
It is claimed by German investigators that this radial 
mass motion of the water is the most important factor 
in damaging targets at close range. At greater dis¬ 
tances it is not effective because, due to the spherical 










RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


31 


symmetry of the system, the kinetic energy of the out¬ 
flowing water falls off as the fourth power of the dis¬ 
tance. The maximum kinetic energy of the water is 
very simply related to the cube root of the period of 
the bubble oscillation. 17 

In addition to the radial motion of the water, there 
is also an upward mass motion of the water resulting 
from the migration of the gas globe. The upward mi¬ 
gration, which for 300 lb of TNT is of the order of 
15 ft, occurs during the very short interval of time 
when the bubble is nearer its minimum size. Thus ve¬ 
locities in excess of 100 fps may be realized. If one 
visualizes a spout of water projected upward with this 
velocity and striking a ship, considerable damage 
might be expected to occur. There is, however, no 
direct evidence at present that actual cases of ship 
damage can be attributed to this cause. 

From the preceding discussion it is apparent that 
much more information must be accumulated before 
it will be possible to assess the relative importance of 
the various factors which may cause damage. The ex¬ 
perimental study is complicated by the fact that the 
bubble phenomena, due to their independence on grav¬ 
ity and the effects of free and rigid surfaces, cannot 
be scaled in any simple manner. 

12 7 Surface Phenomena 

One of the most spectacular effects of underwater 
explosions is the surface phenomena associated with 
them. If the charge is exploded at a fairly shallow 
depth, a great mass of water is thrown into the air. The 
more careful analyses of these effects show that they 
consist of several parts. If the charge is not too shal¬ 
low, the first effect which is noticed is the radial 
spreading of a black ring, immediately followed by 
the formation of a “dome” of white spray thrown 
up off of the water. At a later time, of the order of 
seconds for 300-lb charges, high plumes of water 
break through the dome and rise to a much greater 
height. There may be several separate plume phe¬ 
nomena. Sometimes these plumes are black, as if they 
contained products of combustion, such as free carbon. 
It is currently assumed on the basis of very good evi¬ 
dence that the first effects are due to the arrival of 
the shock wave at the surface. This shock wave, as 
mentioned above, will be reflected from the free sur¬ 
face as a wave of tension. If one plots the pressures 
and tensions to be expected beneath the surface as a 
function of time, one sees that cavitation should occur 
at a small depth beneath the boundary, thus essen¬ 
tially peeling off a layer of water. This layer will pos¬ 


sess a considerable upward velocity because of the 
passage of the shock wave upward and the reflected 
shock wave downward. A simple calculation shows 
that if there were no questions of air pressure or air 
resistance, this velocity would suffice to throw the 
water high into the air, of the order of twice the dome 
heights normally observed. On the other hand, if an 
unbroken layer were actually peeled off, it could rise 
only a very few inches under these same conditions 
because of the vacuum underneath it and the pressure 
of the atmosphere above it, forcing it down. It seems 
likely that the irregularities always present on the 


surface cause this layer to be broken into droplets 
almost immediately, so that the atmospheric pressure 
has access to the underside of the broken layer and 
therefore does not influence the phenomenon further. 
It is certainly reasonable to assume that air resis¬ 
tance is sufficient to account for the discrepancy be¬ 
tween the observed dome heights and those calculated 
on this very simple basis. 

The plumes presumably are masses of water forced 
up ahead of the rising bubble. It will be remembered 
that during the contractural phase of the bubble’s 
oscillation, its rise under gravity is very great, so that 
the water immediately above the bubble can acquire 
a considerable upward velocity. Ultimately, the bubble 
itself will break the surface, adding the burnt gases 
and possibly solid particles from the reaction to the 
material thrown upward. Depending upon the exact 
phase of the bubble oscillation at the time of the 
breakthrough, the plume may be very high and nar¬ 
row or spread out in a sidewise direction. If the ex¬ 
plosion is deep enough so that several oscillations of 
the bubble can occur before the gases break the sur¬ 
face, then the bubble pulses can also contribute their 
own spray domes to the picture. It has even been ob¬ 
served that two separate domes can occur, presumably 
due to the sidewise migration of the bubble on its up¬ 
ward path due to special circumstances. The first 
dome, in this case, would come from shock wave and 
the second one from the first bubble pulse. 

When charges are very deep, of the order of 100 
ft multiplied by the cube root of the weight in pounds, 
the obviously visible surface effects, except for the 
ultimate coming to the surface of the broken-up gas 
globe, become increasingly difficult to detect. It has 
been claimed that this depth is critical and is a mea¬ 
sure of the strength of the water to resist the tension 
wave but it seems more likely in the light of other 
experiments that, if the surface were rough enough 
and the phenomenon observed with a high-speed 


^confidential! 






32 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


camera, there would be some effect at almost any 
depth. The possible absence of an effect with a smooth 
surface may be due to the inability of the cavitated 
surface layer to break into droplets under these con¬ 
ditions. Much more study would be required to settle 
these points definitely. 

A knowledge of the mechanism of the various sur¬ 
face effects is important for a number of indirect ap¬ 
plications, such as the measurement of the shock-wave 
pressure, as will be seen later. It should be stated, 
however, that the height of the surface plumes and 
other observed phenomenon should not be interpreted 
in terms of the power of the explosive or the depth 
of the charge without very careful consideration of 
the detailed physics of the phenomenon. Otherwise, 
quite misleading results can be obtained. The use of 
surface effects to determine the depth of an under¬ 
water explosion will be discussed in more detail later. 

128 Underwater Cratering 

A charge exploded on the ocean bottom will pro¬ 
duce a crater the dimensions of which will be a func¬ 
tion of the size of the charge, the nature of the explo¬ 
sive, the depth of the water, and the hardness of the 
bottom. Not very much quantitative information is 
available for predicting underwater cratering, but 
some experiments 35,36 indicate that, roughly, a crater 
of approximately 5.8 cu ft per pound of TNT can be 
expected on a sand or mud bottom. Naturally, a rocky 
or hard bottom will give considerably less cratering. 
This cratering effect is important practically because 
little damage is done to massive underwater obstacles 
outside of the crater produced by an explosion. Cra¬ 
tering is more effective if the explosive is covered by 
a sufficient depth of water. This is to be expected be¬ 
cause otherwise there is a very great loss of energy 
into the air. The scaling laws described above seem 
to hold at least approximately for these cratering 
phenomena. It is, of course, necessary that the sea bed 
be reasonably homogeneous. With this caution in 
mind, a rough estimate can be made by assuming that 
the volume is proportional to the charge weight and 
the dimensions proportional to the cube root of the 
charge weight under conditions where the depth of 
water is likewise proportional to the cube root of the 
charge weight. 

129 Surface Waves 

Another effect of an underwater explosion which 
is closely related to the surface phenomenon described 
above is the production of surface water waves. The 


expansion of the gas bubble and its rise under gravity 
displaces a considerable volume of water upward, 
leading to surface waves spreading out from a point 
above the explosion. It cannot be said that ordinary 
explosives are very efficient producers of such 
waves, 37,38 the energy going into them being a small 
fraction of the chemical energy. Nevertheless, it is pos¬ 
sible with large explosions to produce waves having 
sufficient height to be useful for certain purposes. 

The use of pressure-operated mines by the Germans 
resulted in an extensive investigation of the produc¬ 
tion of surface waves by conventional explosives. 
Such waves will cause pressure variations at the bot¬ 
tom which might be regulated so as to activate these 
mines. A fairly elaborate mathematical theory of the 
production of surface waves was developed 39,40,41 and 
tested experimentally. 37,42,43 The theory was based 
on incompressive hydrodynamics and treated the ex¬ 
plosion as an ideal source. The effect of the bottom 
and of the free surface was taken into account by the 
use of image sources and a perturbation treatment. 
In order to get numerical results, it was assumed that 
the bubble reached a fixed effective volume instantly, 
remained constant during the bubble period, and then 
collapsed instantly to zero volume. In comparing the 
results of the theory with the rather scanty experi¬ 
mental data, it was found desirable to use an empiri¬ 
cally determined effective bubble volume, in order to 
secure a good fit with experiment. More experimental 
data would be necessary in order to determine the 
limits of accuracy of this theory. 

It was found that in order to get waves of more 
than a very few inches in amplitude at distances 
greater than 1,000 ft tremendous charges are neces¬ 
sary. Furthermore, these are more efficient if they are 
divided into a large number of smaller charges spread 
over a greater area. The reason for this is that the 
large lump charge produces a gas bubble whose diam¬ 
eter is greater than the depth of the water under most 
circumstances where these mines would be of interest. 
Consequently, a tremendous amount of energy is lost 
by venting to the atmosphere, whereas if the charge 
is divided into a large number of smaller charges each 
of these has a gas bubble which will not immediately 
vent. The waves also seem to be larger and it is rea¬ 
sonable to expect they would be if the charge is placed 
sufficiently deep. 

1210 Comparison of Explosives 

One of the principal functions of UEItL was the 
comparison of different explosives for effectiveness in 



RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


33 


underwater weapons. Tests were also frequently made 
to prove that minor changes in composition of pro¬ 
duction fillings, especially of the desensitizer compo¬ 
nent, had no detrimental effect on explosive power. 
Early in the development of the laboratory, it was 
realized that production and loading techniques were 
important factors in determining the weapon per¬ 
formance. It was decided, therefore, to develop instru¬ 
mentation applicable to testing the various weapons 
at full scale. 

For this purpose the 76-ft wooden fishing schooner, 
Reliance, was equipped as a floating laboratory. 44 
Because of its reasonably clear deck space and ade¬ 
quate booms, it has proved very well adapted to han¬ 
dling the heavy gear required for positioning the 
charge, gauges, cables, etc., for each shot. Electronic 
equipment for recording the piezo gauge signals was 
compactly installed in one hold. The other hold served 
as a work shop for mechanical gauge maintenance. 

The full-scale service weapons used in most tests 
were loaded at the Naval Mine Depot, Yorktown, 
Virginia. When the pilot loading unit at Yorktown 
was completed and placed in charge of special officers, 
it became possible to get very detailed data on the 
individual test weapons. This was found to be essen¬ 
tial to the proper interpretation of the Reliance 
measurements. 

The tests were usually conducted in Vineyard 
Sound, where water of about 80-ft depth is available 
in several areas. The charge and gauges were set over¬ 
board by the Reliance crew so as to be strung out at 
known distances apart at a uniform depth, usually 
40 ft. This was accomplished by use of a sea anchor 
applying tension to the gauge line, which was sup¬ 
ported at appropriate places by surface floats, the 
Reliance being headed into the tidal current. 

A typical layout, as shown in Figure 13, contained 
up to eight tourmaline piezoelectric gauges at various 
distances from the charge, each with its own electric 
cable to the vessel. In addition, a large number of ball 
crusher gauges and smaller numbers of Modugno and 
diaphragm gauges (see Section 1.4) were mounted 
along the main spacer cable. Several piston-type 
momentum gauges were also used. The charge was 
fired with an electric cable when all the gear had been 
put in position. The explosion would sever the gear 
into two portions (see Figure 13), the sternmost por¬ 
tion being cut loose from the vessel. After retrieving 
the forward portion of the gear, the Reliance then 
turned and picked up the rear set of buoys, gauges, 
etc. Although occasional trouble due to damage of 


floats was encountered, in general the Reliance was 
able to make one or more shots every day as a matter 
of routine. 

The success of this type of work depended entirely 
upon the quality of the personnel involved and their 
strict adherence to the necessary precautions. Experi¬ 
ence on the part of the scientific staff demonstrated 
that meticulous care in the handling of all types of 
gauges was required in order to secure accurate and 
reproducible results. The crew of the Reliance was 
very conscientious in carrying out instructions re¬ 
ceived from the scientific staff and, of course, there 
were always several scientists on board. It would 
have been impossible to do this type of work success¬ 
fully with a crew which changed from day to day 
or which was not entirely conscientious in performing 
its duties. The captain of the Reliance commanded 
and coordinated the gear-setting operations, after 
which the scientific personnel conducted their work. 
The captain was directly responsible to a research 
supervisor in charge of the Reliance program. 

A considerable number of different explosives were 
compared. 45 ' 51 The quantities measured were the peak 
pressure, impulse, and energy flux in the shock wave 
as given by the piezoelectric gauges, the relative peak 
pressure as estimated from the mechanical gauges, 
and the relative impulse as estimated with the piston- 
type momentum gauges. Table 3 shows the average re- 


Table 3. Results of explosive comparisons relative to 
TNT for constant volume of explosive. 


Explosive* 

Density 

(g/cm3) 

Pressure 

ratio 

Impulse 

ratio 

Energy 

ratio 

Torpex-2 

1.71 

1.16 

1.27 

1.53 

HBX 

1.65 

1.13 

1.25 

1.45 

Minol-2 

1.64 

1.08 

1.26 

1.40 

Tritonal 

1.70 

1.05 

1.18 

1.19 

RDX-Comp.-B 

1.60 

1.10 

1.08 

1.21 

TNT 

1.55 

(1.00) 

(1.00) 

(1.00) 


* See Table 1 for composition of explosives. 


suits of these explosive comparisons. In most cases, 
these numbers are averages over a fairly large number 
of different types of service weapons such as the Mark 
6 depth charge, Mark 54 depth bomb and the Mark 13 
aerial mine. The ratios of peak pressure are probably 
correct to 2 or 3 per cent. The various measurements 
on each different explosive have been reduced to a 
common density for that explosive, since the perform¬ 
ance is a function of density of loading. The outstand¬ 
ing result of these investigations is the establishment 
of the importance of aluminum as a constituent of 
military explosives. This fact was well appreciated 


^CONFIDENTIAL 













RIG USED FOR RELIANCE TESTS 


34 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 
























































































RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


35 


and utilized by both the Germans and the British 52 
quite early in the war. Arguments on the basis of 
oxygen balance give very misleading results. For ex¬ 
ample, TNT is oxygen deficient from this viewpoint, 
so that the addition of aluminum to TNT makes the 
oxygen balance very much worse. Nevertheless, this 
addition increases the performance of TNT. The rea¬ 
son for this is the very great energy release when 
aluminum combines with oxygen. This energy is so 
large that it is advantageous to rob the carbon of 
oxygen and give this oxygen to the aluminum, even 
when there is not enough oxygen to convert all the 
carbon to carbon dioxide. There seems to be no good 
evidence that the water is involved appreciably in the 
reaction as has been sometimes suggested. The pos¬ 
sibility of the reaction of water during an explosion 
could conceivably be settled by making especially 
smooth spherical charges and comparing their power 
with charges having rough surfaces. When the surface 
is smooth, the gas globe also is very smooth, whereas, 
with a rough charge surface there is some tendency 
for Munroe jet action to reproduce irregularities in 
the gas globe. With a smooth gas globe, it is very hard 
to see how sufficient mixing could take place for the 
water to enter the reaction to any great extent. 

Torpex was the most powerful of the explosives 
actually used in any appreciable quantity. However, 
it is probably somewhat more sensitive than is desir¬ 
able in a military explosive. For this reason, following 
certain British work, HBX was developed by the 
Bureau of Ordnance in cooperation with Divisions 8 
and 2 of NDRC. HBX consisted essentially of torpex 
with 5 per cent of a desensitizer added (see Table 1). 

Unfortunately, no general agreement has been 
reached as to whether it is peak pressure, impulse 
energy, or bubble energy which is the determining 
property of an underwater explosion for producing 
damage. Consequently, there is the possibility that 
two explosives might be tested, one of which was supe¬ 
rior in one respect and another in another respect. On 
the basis of present information, it would be difficult 
to make a decision between such a pair of explosives. 
Fortunately, no such dilemma arose with the materials 
which were under consideration during the war. In 
most cases, the more powerful explosive as rated by 
one quality also ranks higher in all of the other 
qualities at the same time. This is not necessarily true, 
and evidence of deviations from this rule are seen in 
the table. 

It will be noted that ratios of peak pressures for the 
commonly used explosives range up to about 1.16. 


It may well be asked whether a 16 per cent improve¬ 
ment in peak pressure is worth striving for. The im¬ 
portance of this 16 per cent improvement may be 
made more striking by considering the volume within 
which the peak pressure exceeds a certain minimum 
amount. This volume will be approximately 60 per 
cent greater for the explosive which has 16 per cent 
higher peak pressure at ecpial distances. To achieve 
such an improvement is worth a considerable effort 
from a military viewpoint. 

The testing procedures described above were exten¬ 
sively used during World War II at UERL and the 
results were in part responsible for the extensive use 
of torpex and HBX as aircraft depth-bomb fillings. 
In attacks against submarines the important factor 
in explosive effectiveness is the range at which the 
weapon is capable of disabling or sinking the sub¬ 
marine. For 250 lb of torpex, the range for sinking 
appears to have been 20 ft or more in attacks against 
most types of submarine encountered. Comparison of 
shock-wave parameters at 20 and 30 ft thus provides 
a reasonable basis for assessing explosive effectiveness 
for this purpose. 

On the other hand, there is a certain amount of 
evidence that only about half as much torpex as TNT 
is required to produce equivalent damage in the case 
of contact explosions. As discussed in Section 1.2.6, 
this would seem to support the view that the mass 
flow of water against the target was the important 
factor for damage close to the charge. The energy 
available by this mechanism is related to the gas 
bubble energy which in turn is proportional to the 
cube of the bubble period. In fact, most German com¬ 
parisons of explosives were based upon relative bubble 
period measurements. Since, on an equal-volume 
basis, the bubble period for torpex is 1.22 times that 
of TNT, the effectiveness of torpex in, for example, 
a contact torpedo war head, would be estimated to be 
about 1.8 times that of TNT. The preference on the 
part of most American submarine commanders for 
torpex war heads can be readily understood on the basis 
of this difference. 

It is interesting to note that the radically different 
German and American procedures for comparison of 
explosives were probably valid and justified consider¬ 
ing the prime use with which each side was concerned. 
The Germans were concerned with contact or near- 
contact weapons for use against shipping and the 
Americans with maximum lethal-range depth bombs 
for use against submarines. 

Bubble period measurements were made at UERL 


I i ON FTDENTIAL 








36 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


on small scale (Mz-lb) charges of tetryl, TNT, and 
torpex and on large scale (250-lb) charges of TNT 
and minol. The results were not, however, considered 
in connection with explosive comparisons. 

1,211 Importance of the Use of 

Statistical Methods 

The problem of comparison of explosives discussed 
above is an illustration of a type of situation often 
encountered where statistical analysis of experimental 
data is highly important. In many basic measure¬ 
ments, experiments can be performed with such pre¬ 
cision that little consideration of statistical questions 
is necessary, but often in practical problems, especial¬ 
ly in the comparison of explosives, all measurements 
cannot be performed with as high a degree of accuracy 
as would be desirable. This is due to the fact that it 
may be difficult to recognize and control all the fac¬ 
tors which might influence the measurements. In de¬ 
ciding whether a new type of explosive is really supe¬ 
rior to older types, one should bear in mind that ser¬ 
vice weapons loaded by normal procedures are not 
absolutely uniform and reproducible. For example, 
the weight, density, and quality of the cast explosive 
is noticeably variable. Therefore, it is obviously dan¬ 
gerous to base decisions on the measurements of a 
small number of charges. Furthermore, even when a 
sufficient number of experiments have been carried 
out, a careful statistical treatment of the data is de¬ 
sirable in order to determine the degree of confidence 
which can be associated with the results. There are a 
number of basic principles which are applicable to 
the problem of explosive evaluation. 53,54 

The first principle is that controls should always 
be used. That is to say, in any series of experiments 
in which new materials or new methods are being 
tested, there should be an ample number of tests on 
standard materials or methods. Thus, in testing ex¬ 
plosives at UEEL, charges of TNT were always in¬ 
cluded in each series, so that any variation of the test 
conditions, due to any cause whatsoever, which might 
change the absolute level of the pressures, impulses, 
etc., would at least largely cancel because ratios of 
these quantities to the corresponding quantities for 
TNT were always employed. In many cases the per¬ 
sons responsible for instrumentation may feel highly 
confident that they have brought under control all the 
variables which influence the result appreciably and 
that it is, therefore, unnecessary to employ controls. 
Experience has almost universally shown that this is 


not a safe procedure and that unknown forces of vari¬ 
ation are very likely to appear, even with test methods 
which have been highly developed and long used. For 
example, at UEI1L the diaphragm gauges mentioned 
above were developed quite early to a state of high 
reproducibility. After several months’ use of this 
gauge, a sudden shift in values occurred which proved 
very difficult to locate. A long search located the 
trouble as due to a change in the grade of lumber 
supplied for making the frames to hold the gauges. 
As a result of this experience, controls were rigidly 
required thereafter in all tests. 

A second basic principle is that the controls and 
the test specimens should be measured under as nearly 
identical conditions as possible. This normally in¬ 
volves testing them at close intervals of time, because 
it is very difficult to reproduce, after a long interval, 
all the conditions which initially existed. It was, there¬ 
fore, a standard practice at UERL to test explosives 
in strings. That is, a number of different explosives, 
including TNT as a standard, were tested either the 
same day or on successive days with the same equip¬ 
ment and methods. Furthermore, the order in which 
the different materials were fired was chosen by lot 
so as to minimize any possible effect of systematic 
changes of various variables with time. For example, 
if every day the explosives in a string had been fired 
in the same order, it might have been possible for a 
systematic error to enter because the temperature was 
always colder the first thing in the morning than later. 
Because the accuracy of the measurements and the 
reproducibility of charges were not sufficient to make 
one measurement of each substance adequate, the 
strings were repeated a number of times, in each of 
which the order was chosen independently by lot. 
The number of strings required was calculated in 
advance by standard statistical methods on the basis 
of the expected precision of the individual measure¬ 
ments and the desired overall accuracy. 

In carrying out these repetitions to the strings, 
another principle was employed. Since the conditions 
under which explosives are used in practice are ex¬ 
tremely variable, it is not sufficient to make tests 
under only one set of conditions. Thus it was at least 
conceivable in advance of the experiments that the 
relative merit of two explosives might be a function 
of the distance from the charge, the size or shape of 
the charge, etc. Since it was desired to obtain an over¬ 
all answer to the question of how much better an 
explosive N is than TNT, the experiments had to be 


L i OX FIDEXTIAL 







RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


37 


performed over a range of conditions. Therefore, in¬ 
sofar as it was feasible, each string was measured 
under somewhat different conditions although, of 
course, every shot inside a given string was carried 
out under the same conditions. From string to string, 
some variable was changed which was not expected 
to cause any shift in the relative effectiveness of the 
explosive. By proceeding in this way it was possible 
to determine the effect of such variables. The ratios 
of explosive performance obtained in the different 
strings could still be averaged together to get an 
overall average ratio applicable to the range of con¬ 
ditions employed. The average would be more accurate 
and reliable than the results of any individual string. 

A fourth principle was to choose by lot the values 
of any presumably unimportant variables which could 
not be controlled from measurement to measurement. 
For example, in using the diaphragm gauges, the steel 
plates could be used only once and the plates as re¬ 
ceived from the manufacturer might have been ar¬ 
ranged in an order leading to a systematic variation of 
thickness or strength from one plate to the next. The 
plates of each lot were thoroughly shuffled, so that 
any accidental variations would enter the results as 
random error and not as a systematic error tending 
to falsify the conclusions. 

Every effort was made to avoid subjective errors. 
Frequently the explosive being tested was identified 
only by number, so that those carrying out the tests 
and analyzing the results would not know the iden¬ 
tity of the materials. Thus there was little chance of 
the subconscious influence of prejudice on the answer. 
The frequency with which prejudice unintentionally 
influences the results of scientific experiments is not 
sufficiently appreciated. 

Considerable attention was paid to the estimation 
of experimental errors from the data itself. Gauges 
were normally used in pairs, so that the differences 
between members of a pair when averaged over many 
experiments would give a good estimate of the reli¬ 
ability of a gauge. In this way, a decision could be 
made on the basis of a standard statistical argument 
as to whether a given observed difference between two 
explosives was likely to be real or merely the result 
of experimental error. 

1212 Absolute Values of Shock-Wave 

Parameters 

Since the explosive comparison experiments were 
so designed that ratios were obtainable from identical 
gauges under conditions as nearly the same as pos¬ 


sible for the various explosive compositions, small 
errors in the absolute calibrations tended to cancel. 
Nevertheless, considerable effort was expended to per¬ 
fect the instrumentation so as to yield absolute values 
of the shock-wave parameters because of their im¬ 
portance in studies of damage processes. 

Figures 14, 15, and 16 give the peak pressure, im¬ 
pulse, and energy flux respectively for charges of 



Figure 14. Plot of P versus W^/R for spherical 
cast TNT. 


TNT as functions of W*/R. Over the range of 
these measurements, the shock-wave parameters are 
represented with fair accuracy by the following linear 
equations 


Peak pressure 


/ Wi V-i2 

P = 2.12 x 10M psi, 


/ \ 0,89 

Impulse 1 — 1.4611—f psi-sec, 

/ Wi \ 2.05 

Energy flux E = 2.40 x 10 ! WG _ J psi-in, 

where W*/R is expressed in Ib^/ft. Impulse and energy 
flux are calculated to the time t = 6.7(9 sec only, i.e., 
6.7 times the time constant of the shock wave. The 
energy factor given here is calculated on the acoustic 
approximation 



where p is the density and c the velocity of sound 
for sea water. 


















































38 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


The true energy flux would include terms for the 
finite amplitude effect 55 and for the mass motion of 
the water radially outward from the charge surface 
(see Section 1.2.6). At the distances from the charge 
over which these equations are intended to apply, 



i/ i/ 

W 3 /R IN LB 3 /FT 

l i 

Figure 15. Plot of I/W s versus W°/R for spherical 

cast TNT. 

neglect of these factors does not seriously invalidate 
the results. Experimental data is not yet available 
which would make possible the evaluation of the total 
energy flux over a complete bubble expansion. 

Procedures employed to overcome various difficul¬ 
ties encountered in attempts to establish the absolute 
level of the piezoelectric results are described in Sec¬ 
tion 1.4.1. By the end of World War II it was be¬ 
lieved that the controlling factor in limiting the pre¬ 
cision of the absolute values was the difficulty of ob¬ 
taining precise determinations of the piezoelectric 
constant of the tourmaline gauges. In principle, this 
calibration should be carried out under conditions 
closely approximating those in the shock wave being 
measured. Since a calibration of this type is extreme¬ 
ly difficult to accomplish, several independent methods 
of estimating shock-wave peak pressures were em¬ 
ployed to test the reliability of the piezoelectric 
results. 

1. For four shots in which it was used, the optical 
distortion method described in Section 1.4.3 gave 
pressures which were approximately 10 per cent 
greater than those measured by the piezoelectric 
gauges. Unfortunately, sufficient work was not done 


to determine the accuracy of this method. 

2. A second check which has the advantage of sim¬ 
plicity was provided by the measurement of the veloc¬ 
ity of rise of the spray dome from the surface above 
an explosion. The pressure P at any point in the 
water is related to the propagation velocity of the 
shock wave U and the particle velocity u by the 
simple equation 

P = pUu, 


where p is the density of the water. Values of the 
shock-wave propagation velocity U are shown in 
Figure 17. 56 It has been shown 57 ' 59 that to a good 
approximation u = V/2, where V is the velocity of 
rise of the spray dome. The factor Vfc enters because 



Figure 16. Plot of E/W 3 versus W' s /R for spherical 
cast TNT. 


^CONFIDENTIAL - 




























































































































































































RESULTS OF UNDERWATER EXPLOSION INVESTIGATIONS 


39 


the reflected rarefaction wave doubles the upward 
velocity of the spray. The latter was measured by 
means of a high-speed streak camera. 60,61 Table 4 
shows a comparison of the pressures obtained by this 
method with the corresponding piezoelectric gauge 
values. 


Table 4. Comparison of pressures from dome 
velocity and piezoelectric gauge measurements for 
TNT charges. 


Charge- 

Distance 

Pressure (psi) 

weight 

to charge 

By dome 

By piezo- 

(lb) 

(ft) 

velocity 

electric gauge 

5.07 

4.00 

7,680 

7,800 

5.53 

4.00 

8,150 

8,100 


3. The ball crusher gauge, described in Section 
1.4.2, provided a further check on the absolute- 
pressure level of the piezoelectric gauges. Pressures 
obtained with the ball crusher gauge on 300-lb charges 
were in agreement with the piezoelectric gauge values 
to within ±5 per cent. 

4. Only a very rough check was made by measure¬ 
ment of the propagation velocity of the shock wave 
U. From the Pankine-Hugoniot conditions (see Sec¬ 
tion 1.2.13) and an equation of state for water, 56 ’ 02 
the following approximate relation valid to a pressure 
of approximately 20,000 psi may be derived: 

U—c 

- = (5.4 x 10-°)P . 

c 

The pressure is thus directly dependent on the quan¬ 
tity U—c which, except at very high pressures, is 
small and therefore difficult to measure experimentally 
with the required accuracy. 

5. An additional check on the calibration of the 
piezoelectric gauges was due to the reciprocity calibra¬ 
tion method developed at the Underwater Sound Ref¬ 
erence Laboratory [USRL] of Division G, NDRC. 63 
Some tourmaline gauges of the type used for the 
underwater explosion measurements were calibrated 
by this method and gave values in good agreement 
with those obtained by the usual static calibration 
methods. 

1.2.13 Theoretical Studies of Shock-Wave 
Propagation and Intensity 

Relation between Peak Pressure and Velocity 
or Propagation of Shock Waves 

The velocity of propagation of a shock wave depends 
upon its peak pressure in a way that can be calculated. 
This velocity is higher than the velocity of sound 


when the peak pressure is high but approaches the 
velocity of sound as the peak pressure decreases. The 
mathematical relationship is based on the laws of 
conservation of matter, conservation of momentum, 
and conservation of energy. The resulting equations 
are known as the Rankine-IIugoniot relations. 64 Ap¬ 
plication of these relations requires, in addition, a 
knowledge of the effect of temperature and pressure 
on the density of water (or sea water). 

Figure 17 shows the results of a calculation for 
sea water of the relation between the excess shock 
velocity (i.e., shock velocity minus sound velocity) 
and the shock wave pressure. 56,62 This relationship 
enters into any theoretical calculations on shock-wave 
propagation and also has direct practical applications. 
In Section 1.2.12 it is mentioned that measurements 
of shock-wave velocity, combined with the above law, 
were investigated as a possible independent check on 
other methods for measuring the absolute value of 
the shock-wave pressure. In any measurements involv¬ 
ing times of propagation, such as in depth ranging 
(Section 1.4.5), this excess velocity must be con¬ 
sidered if the pressure is considerably greater than 
acoustic levels. 

Theoretical Calculation of Shock-Wave 
Properties 

It proved to be possible to predict by purely theo¬ 
retical methods the peak pressure and other shock- 
wave parameters as functions of distance from charges 
of various explosives. Work carried out under Divi¬ 
sion 8, 3,4 yielded estimates of the pressure within the 
explosive charge itself at the instant of complete de¬ 
tonation. As an approximation it was usually assumed 
that the pressure inside was the same throughout a 
spherical charge and that the burnt gases were at 
rest at that instant, although actually it was known 
that the mechanism was more complicated. With this 
starting point, it is a purely hydrodynamical prob¬ 
lem, but a very difficult one, to calculate the events 
which occur in the surrounding water as the pressure 
wave is emitted. 

The equation of continuity (conservation of mat¬ 
ter) and the equation of motion (conservation of 
momentum) supply a set of differential equations for 
the motion of the water which, in principle, determine 
the events accompanying expansion of the explosion 
products once the boundary conditions are specified. 65 
The boundary conditions are given on the one hand 
by semiempirical relations describing the way in 
which the pressure of the burnt gases falls off as the 


^TOXl-'lBKXTTAL 























40 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 



PRESSURE IN 10 PSI 

Figure 17. Curve showing dependence of propagation velocity and particle velocity on pressure of shock wave. 


gas bubble expands, 00,67 and on the other hand by the 
Hugoniot relations between the shock-front pressure 
and velocity. It has not yet proven feasible, however, 
to solve differential equations exactly for this problem. 

One procedure which was used to get an answer 
for one case (TNT) was numerical integration. 68 " 70 
This led to reasonably good results but was so exces¬ 
sively laborious that it was not applied to other mate¬ 
rials or to other densities of TNT. 

An approximate solution was found at Cornell Uni¬ 
versity which was remarkably successful. 71 * 74 In that 
solution, the pressure, etc., inside the explosion were 
obtained from a theoretical treatment involving nu¬ 
merous approximations, and the solution of the hydro- 
dynamic problem of the propagated pressure wave nec¬ 
essarily required certain compromises with rigor.When 
these simplifications were made a complicated but 
tractable solution of the differential equations was 
obtained, and applied to a considerable list of explo¬ 
sives at several loading densities. 75 * 80 The results in 
terms of explosive comparison ratios relative to TNT 


for a few explosives are listed in Table 5. These values 
are to be compared with the corresponding experi¬ 
mental ratios shown in Table 3. The theoretical values 


Table 5. Theoretically computed explosive ratios 
for constant volume comparison relative to TNT. 


Explosive* 

Density 

Peak 

pressure 

ratio 

Impulse 

ratio 

Energy 

ratio 

Torpex-2 

1.70 

1.10 

1.16 

1.28 

Minol-2 

1.65 

1.05 

1.11 

1.17 

RDX-Comp.-B 

1.61 

1.06 

1.07 

1.13 

Amatol 

1.55 

0.94 

0.92 

0.87 

TNT 

1.59 

(1.00) 

(1.00) 

(1.00) 


* For composition of explosives see Table 1. 

are somewhat lower than experiment but they do give 
the correct order of merit of the different explosives. 

Later a different type of approximation was used 
which also enabled the peak pressure and impulse to 
he calculated as functions of distance and charge 
weight. 81 * 83 In this treatment, certain measured para¬ 
meters of the shock wave at a given distance could be 


















































DAMAGE PRODUCED BY UNDERWATER EXPLOSIONS 


41 


used to compute the shock-wave parameters at other 
distances, hence the description of this theory as a 
propagation theory. This method was considerably 
simpler than the earlier procedure and had the advan¬ 
tage of being applicable to shock waves in air as well 
as water. (See Chapter 2.) 

Figure 18 shows a comparison of the peak pressure 
versus distance curves for TNT for the theoretical 
calculations and for some measurements with piezo 
gauges at UERL. The agreement is really quite re¬ 
markable for so complicated a phenomenon. As a 
matter of fact, during the period in which the piezo 
gauges were still in a development stage at UERL 
the calculated results were usually the values utilized 
since they were regarded as more reliable than any 
experimental values then available. 

The theoretical investigations at Cornell involved 
very difficult and abstract mathematical methods and 
it was not at all certain at the time they were under¬ 
taken that they would lead to results of any practical 
value. As a matter of fact, the investigations proved 
to be extremely useful, not only because of the direct 
applications of the numerical values of pressures, etc., 
but because the theory served as a guide and frame¬ 
work for the experimental work at UERL. There was 
constant competition between the experimental and 
theoretical workers in seeking the ultimate answers, 
and discrepancies which sometimes appeared lead to 


searches for errors and effects which otherwise might 
not have been suggested. 

13 DAMAGE PRODUCED BY 

UNDERWATER EXPLOSIONS 

131 General Considerations 

The problem of predicting the damage to a given 
structure which will be caused by an underwater ex¬ 
plosion is very difficult and has not yet been fully 
solved. In principle, the problem is nothing more 
than the application of Newton’s laws of motion and 
of the resisting properties of the material. The diffi¬ 
culties arise from the complexity of the system of 
forces acting on an element of the structure as it is 
being deformed by the explosion. Usually the complete 
expression of these forces is not known or the solu¬ 
tion of the resulting equations is not feasible. When 
simplifying approximations are made to render the 
problem tractable, some uncertainty is introduced as 
to the confidence with which one can apply the theo¬ 
retical results to the interpretation of experiments 
on an actual structure. In view of the difficult nature 
of the problem, it is not surprising that reasonably 
complete theory is available for only certain simple, 
idealized target structures such as, for example, a 
circular steel diaphragm having its edge rigidly sup- 



1 1.5 2 2.5 3 4 5 6 7 8 9 10 15 20 25 30 40 


R/a 0 

Figure 18. Curve of theoretically computed pressures for cast TNT versus distance from charge. Curve A: approximate 
analytical solution; Curve B: “propagation theory”; Curve C: numerical integration treatment. 












































42 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


ported. In the case of ship structures it is even difficult 
to state which properties of the explosion are the most 
important in producing damage in a given case. It is 
conceivable that under certain conditions the damage- 
determining factor could be shock-wave peak pres¬ 
sure, impulse or energy, the properties of the bubble 
pulses, or the incompressive flow of the water associ¬ 
ated with bubble motion. Nevertheless, certain con¬ 
cepts of the damage theories at least define the limita¬ 
tions on possible hypotheses concerning the nature 
of the damage process. 

The theories so far developed are primarily appli¬ 
cable to noncontact explosions, for example, a depth 
bomb exploded near a submerged submarine or a 
large aerial bomb exploded in the water at a distance 
from a merchant vessel but near enough to produce 
serious damage. Under these conditions, especially 
where the charge is at the same level as the target 
and not underneath it, the kinetic energy effects due 
to the incompressive flow of the water can probably 
be ignored, since, as pointed out in Section 1.2.6, 
these effects fall off as the fourth power of the dis¬ 
tance, whereas the energy transported by the shock 
wave falls off only as the second power of the distance. 
For charges at a distance from a target, the double 
pulses are probably not important. In many cases, 
the explosion occurs too near the surface for these 
pulses to develop because venting occurs first. In other 
cases, such as in a deep attack on a submarine, bubble 
pulses might have to be considered, especially if the 
charge detonates underneath the target. This is a 
subject which needs further investigation. 

The subject is particularly confused for contact or 
near-contact explosions. Under these circumstances, 
the shock-wave phenomena and flow phenomena occur 
almost simultaneously and the target, if close enough 
to the charge, will be subjected to quite a high pres¬ 
sure from the «'as bubble itself. 

O 

Effect of Target Inertia 

When a shock wave strikes a target of large area 
so that the effects of the edges do not need to be con¬ 
sidered, a number of possibilities exist. If the target 
is quite massive so that its inertia is large and the 
time required for it to accelerate appreciably is large 
compared to the duration of the shock wave, the im¬ 
pulse of the wave will be completely absorbed by the 
target, and impulse will then be the deciding factor 
in determining the extent of damage. This is similar 
to the experiment in which a bullet strikes a ballistic 
pendulum. The period of the pendulum is long com¬ 


pared with the time of impact of the bullet and one 
thus measures the total impulse transferred by the 
bullet to the pendulum. Furthermore, one can treat 
the reflection of the wave as if the target were rigid, 
so that the pressure and likewise the impulse are essen¬ 
tially doubled by this reflection. The question as to 
whether or not damage takes place then becomes a 
problem of calculating whether the target is capable 
of absorbing the given amount of impulse without 
suffering permanent deformation. As a simple illus¬ 
tration, consider a completely free, air-backed plate 
upon which a shock wave impinges perpendicularly. 
If the plate has the mass M and the impulse in the 
shock wave has the value I, the plate acquires a mo¬ 
mentum Mv = 21, where v is the velocity acquired 
by the plate and the factor 2 occurs because of the 
reflection of the shock wave. 

On the other hand, the damage process is different 
when the target plate is so light that its inertia does 
not prevent appreciable motion during the time of 
passage of the shock wave. In the limit when the 
plate is so light that it accelerates rapidly compared 
with the duration of the shock wave one might expect 
that the peak pressure would be the important damage 
determining factor. If the possibility of cavitation is 
ignored this would follow because the damage would 
be over before the pressure in the shock wave had 
fallen appreciably below its peak value. Under these 
conditions the ultimate duration of the shock wave 
would have no important bearing on the extent of 
the damage. This extreme situation is the sort that 
would be expected with a very large explosion, such 
as an atomic bomb. Here, the full duration of the 
wave is longer than the period of most target struc¬ 
tures so that the damage is measured by the peak 
pressure and not by the impulse or duration. 

Effect of Cavitation 

Under certain circumstances cavitation can occur. 
This greatly complicates the treatment of the damage 
problem. When the target accelerates under the action 
of the shock-wave pressure, its motion forward tends 
to reduce the pressure in the water. If the target is 
light enough, this effect can be so pronounced as to 
cause the pressure to fall very rapidly below zero to 
negative values. In other words, the plate acquires 
sufficiently great velocity actually to pull away from 
the water or to cause the water to pull away from it¬ 
self, resulting in the formation of cavitation bubbles. 
Figure 11 (see Section 1.2.5) shows such cavitation 
in front of a thin air-backed free plate accelerated by 








DAMAGE PRODUCED BY UNDERWATER EXPLOSIONS 


43 


a shock wave. A theory has been developed to take 
into account this phenomenon in the simple idealized 
case of a deformable diaphragm with supported edges. 
The net result of this theory is that the energy of the 
shock wave becomes trapped between the target plate 
and the receding layer of cavitation bubbles. This 
layer recedes because the plastic deformation of the 
moving plate absorbs its kinetic energy and thus ar¬ 
rests its forward motion. When this happens, the 
water which is moving forward piles up against the 
plate and the pressure once more rises to positive 
values so that the cavities begin to collapse. This 
boundarv between solid water and cavitated water 
then recedes away from the target plate. The mathe¬ 
matics leads to the predictions that, under these cir¬ 
cumstances, it will be the square root of the energy 
of the shock wave which is the determining factor for 
damage. 

c 

Edge Effects 

The damage process for all actual cases is compli¬ 
cated by edge effects. A real target is not of infinite 
extent, so that the phenomena occurring around the 
edges of the target will influence the phenomenon at 
the center. A finite time is required for any disturb¬ 
ance to be propagated through either the sea water 
medium or the target structure so there will be a time 
factor in the influence of edge effects, but they will 
eventually act to influence the phenomena at any part 
of the structure. Thus, if the target is of small diam¬ 
eter, cavitation may never get started because the re¬ 
duction in pressure at the center caused by the for¬ 
ward motion of the target plate may be eliminated 
by the flow of pressure in from the high-pressure re¬ 
gions around the plate. This diffraction effect was 
used to predict quantitatively the conditions under 
which cavitation will occur. 84,85 The predictions so 
obtained were successfully borne out by underwater 
photographic investigation of cavitation phenomena. 
(See Section 1.4.3.) 

Delation of Shock-Wave Parameters to Damage 

It is seen from the above discussion that peak pres¬ 
sure, the square root of energy, or impulse may each 
in its own domain be the determining criterion of 
damage. In all real cases, the mechanism will be some 
combination of these idealized ones. It is unfortunate 
that no more definite answer to this question lias yet 
been made which is applicable to practical situations, 
because a knowledge of which of the characteristics 
is the important one would enable a determination 


of the optimum weapon size to be made. 86 Thus, if 
peak pressure is determining, the lethal radius will 
be proportional to the cube root of the charge weight 
on the basis of the similarity law; whereas, if impulse 
is effective, the lethal radius will increase approxi¬ 
mately as the two-thirds power of the weight. Finally, 
with the square root of the energy, the lethal radius 
would increase approximately as the square root of 
the weight, that is, intermediate between the peak 
pressure and impulse cases. Since, in practice, one 
never gets either the pure peak pressure or the pure 
impulse cases but something intermediate, the square 
root law is normally not a bad approximation. Given 
the proper law to apply, one could calculate the op¬ 
timum weapon size using knowledge of the modes of 
attack and the geometry of the target. Thus, it could 
turn out, with a very small target, that the important 
factor was the lethal volume, that is the volume 
around the explosion within which the target would 
be damaged. This lethal volume would vary as the 
cube of the lethal radius and, therefore, as the % 
power of the weight if the square root law applied. 
Under these conditions, the probability of damage 
would increase more rapidly than the weight of the 
charge and would thus favor large charges. However, 
as the charge weight increases to large values, the 
increase in the time constant of the shock-wave decay 
would cause the damage-distance exponent to decrease 
toward the peak pressure-distance decay exponent 
which would ultimately make the lethal volume pro¬ 
portional to charge weight. The lethal volume crite¬ 
rion is certainly not the proper one to use in all cases. 
For example, if the depth of the target is known and 
the depth of the explosion can be accurately set, lethal 
area would be a more appropriate criterion. The prob¬ 
lem is thus complicated but should be soluble if the 
conditions are known in detail. 

13 2 Explosive Damage to Steel Plates 

Although it should be clear from the above para¬ 
graph that the state of knowledge concerning damage 
to structures in general from underwater explosions 
is not in a satisfactory state at the present time, never¬ 
theless, simple idealized systems have been effectively 
studied both experimentally and thoretically and pro¬ 
vide a useful basis for further work. The simplest of 
these systems is the free air-backed plate. Some ex¬ 
periments have been performed on this type of system 
especially with the aid of underwater photography. 13 
Complications here are the edge effects and the pro- 









44 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


duction of cavitation under certain conditions, so that 

even this very simple system has not been fully treated 

theoreticallv. 

•/ 

Another simple system which has been treated is 
the ball crusher gauge in which a copper sphere is 
damaged by the pressure wave accelerating a piston. 
This is discussed in Section 1.4.2. 

Circular Steel Diaphragm Experiments 

The UEI1L diaphragm gauge described in Section 
1.4.2 which consists of a clamped air-backed steel dia¬ 
phragm has been extensively studied both theoreti¬ 
cally and experimentally with quite satisfactory re¬ 
sults. In the course of its use as an empirical measure 
of the effectiveness of various explosives, 15,87 ' 89 a 
large amount of experimental data was obtained with 
a great variety of charge weights and distances. In 
addition, a number of special experiments were made 
on this gauge from the viewpoint of testing the ap¬ 
plicability of theoretical results. 

It was found, for example, that when the charge 
size was of the order of 300 lb or larger, the ratios of 
diaphragm gauge readings for various explosives were 
very closely proportional to the peak-pressure ratios 
from these explosives as measured piezoelectrically. 
However, there was empirical evidence that even with 
charges of this size the diaphragm gauge was not act¬ 
ing as a pure peak-pressure gauge; that is, its read¬ 
ings were somewhat influenced by the rate of decay 
of the pressure pulse. To explore this point, the data 
were analyzed to determine the effect of weight and 

J O 

distance on the damage to the diaphragm. It was 
found that over short ranges of weight and distance, 
the central indentation 8 of the diaphragm could be 
expressed as a simple function of the weight W and 
distance R, i.e., 

CW m 

S = -> 

R n 

where C is an empirical constant related to the gauge 
properties and m and n are empirical constants. Using 
this formula, one can investigate the relation between 
weight and distance which produces a given constant 
damage. If peak pressure were the only factor influenc¬ 
ing the result, the similarity law would show that the 
distance for a given degree of damage should vary as 
the cube root of its weight. In other words, the ratio 
of the weight exponent to the distance exponent 
should be one-third. For large charges, the actual 
value was 0.4, showing that peak pressure was not the 
only factor influencing the results. If impulse had 


been the sole factor, the ratio would be approximately 
two-thirds as calculated from the known dependence 
of impulse on weight and distance. For small charges 
(about 5 lb), the exponents found with the diaphragm 
gauges were 0.6 and 1.2 for weight and distance re¬ 
spectively. The ratio of approximately one-half shows 
that in this region of charge weight the diaphragm 
gauge is measuring something between impulse and 
peak pressure. 

Experiments were performed in which the time re¬ 
quired for the diaphragm to receive its full depression 
was measured by means of an electric contact fitted 
into the gauge. 15 The experiments showed that the 
time was about 150 fx sec, much shorter than the first 
bubble period, unless the gauge was mounted above 
a small charge. Consequently, the great bulk of the 
data obtained with these instruments as employed at 
UERL for explosive comparisons (i.e., gauge hori¬ 
zontal to side of charge) was not influenced by bubble 
pulses. This was further demonstrated by the time of 
action of the gauge as determined approximately from 
experiments in which the depth of submergence of the 
gauge and charge was varied. 90,913 As the two were 
brought closer to the surface, a critical depth was 
reached at which the damage began to decrease with 
closer approach to the surface. The explanation of this 
decrease is that the shock wave reaching the dia¬ 
phragm is cut off by the rarefraction coming from the 
surface. The time at which the pressure wave is thus 
cut off can be calculated from the geometry of the 
setup so that the depth at which the falling off in 
damage begins will give the maximum duration of 
the shock wave which is effective in causing damage. 
This time turned out to be of the order of 200 fx sec 
for charges of a few pounds, in rough agreement with 
the value of 150 fx sec obtained in experiments using 
the electric contact procedure. As mentioned in Sec¬ 
tion 1.4.3, it was found by photographic experiments 
that cavitation did not occur with these gauges under 
normal test conditions, although conditions could be 
devised which would result in cavitation. 

When water-backed instead of air-backed dia¬ 
phragms are damaged, the deformation is consider¬ 
ably less. This reduction is primarily due to the 
inertial resistance of the water which must be accel¬ 
erated by the deforming plate. 

Experiments were performed on the influence of 
diaphragm thickness and diaphragm weight in order 
to compare with the theory discussed below. 

Experiments were also carried out which showed 
the influence of pieces of wood near the diaphragm 


i nKFIDEKTIAfc 






DAMAGE PRODUCED BY UNDERWATER EXPLOSIONS 


45 


gauge to be very marked, so that wooden structures 
should be avoided in using these or other underwater 
pressure gauges. 

Theoretical Calculation of the 
Plastic Deformation 

A number of theoretical treatments of air-backed 
diaphragms were made during World War II. 84,92 ' 96 
The theory developed at Cornell University was based 
on a number of approximations and assumptions, in¬ 
cluding the idea that the deformation of steel could 
be approximately treated mathematically by assuming 
that its stress-strain curve was a horizontal straight 
line at the yield stress. Furthermore, it was assumed 
that the diaphragm could be treated as a membrane 
under a constant tension equal to the product of its 
thickness and the yield stress of the material. It was 
necessary to consider not only the reaction of the dia¬ 
phragm to the load imposed upon it, a problem of 
plasticity, but also the effect of the deformation of 
the diaphragm on the load itself, since the moving 
diaphragm sends out a rarefraction wave. This cor¬ 
rection is complicated by the diffraction effects from 
the region surrounding the diaphragm. The approxi¬ 
mation was also made of linearizing the differential 
equations which were set up. Solutions were obtained 
which gave the deformation to be expected under any 
given condition of shock-wave attack, provided cavi¬ 
tation did not occur. These formulas were remarkably 
successful in predicting the experimental values which 
actually obtained over a very wide range of varia¬ 
bles. 15,97 The theory also indicated the form of the 
dependence of the diaphragm deflection on the thick¬ 
ness 98 and the diameter of the steel plates, the effect of 
bubbles, etc. It was thus feasible, by use of the theory, 
to eliminate the effect of small unavoidable variations 
in plate thickness. Thus in making explosive compari¬ 
sons at UERL it was customary to reduce all gauge 
readings to the corresponding reading for a standard 
thickness of diaphragm. 

The conditions leading to cavitation were success¬ 
fully derived, 84 but there still remains the very diffi¬ 
cult problem of developing an accurate theory for 
predicting the damage under conditions of cavitation. 

1,3 3 Some Remarks on the Use of 

Scaled Models 

One of the most convenient methods of studying 
the phenomenon of damage by underwater explosion is 
the use of scaled models. 99 ' 102 There has been much 
discussion and not a little experimentation in the past 


concerning the reliability of this method of investi¬ 
gation and it cannot be said that the issue with re¬ 
spect to explosion phenomena is completely clarified. 
However, a great deal more is understood now regard¬ 
ing the requirements for true scaling than was known 
at the beginning of World War II. At that time, for 
example, the phenomenon of bubble oscillations was 
not at all well known. Furthermore, the effect of rate 
of strain on the strength of materials was not appre¬ 
ciated. The evidence is now very strong that shock- 
wave properties scale, as described in Section 1.2.4, 
to a considerable degree of accuracy. It is not, of 
course, impossible that more refined investigations 
will detect small deviations from the scaling laws but 
the deviations should not be of great practical sig¬ 
nificance. It is also well known now that the bubble 
effects do not scale in the same way. Bubble effects, 
therefore, immediately put a limitation on the use of 
models for the study of underwater damage under 
conditions such that bubble or flow phenomena may 
be important. There are, however, other limitations. 
The most important limitation is the fact that it is 
almost never possible to build a model which is per¬ 
fectly scaled from a large structure. For example, no 
really equivalent means of fastening the members to¬ 
gether has been found. Bivets and welding are not 
easy to reproduce on a small scale. Neither is it usu¬ 
ally practical to make the structural members of ex¬ 
actly the same shape in the model as in the prototype. 
It is also very difficult to reproduce the properties of 
heavy steel members on a small scale, since the opera¬ 
tion of rolling out thin sheets influences the strength 
noticeably. In spite of all these difficulties, it is un¬ 
questionable that a great deal of essential information 
can be derived from model experiments. 

Naturally, no model experiment is a complete sub¬ 
stitute for a full-scale test on the actual structure of 
interest. On the other hand, the number of variables 
involved and the number of variables which are not 
easily controlled may be so great that a single large- 
scale test can be highly misleading. When an experi¬ 
ment involves either variables which cannot be accu¬ 
rately controlled or variables which take on many 
values in practice, one of which must be selected for 
the test, one has a statistical problem such that only 
a large number of experiments under a wide range of 
practical conditions can give a result of assured accu¬ 
racy. Such a large number of tests is impractical if 
expensive full-scale structures have to be employed. 
It is for these reasons that model investigations are 
practically essential for the study of damage although 


l' 0 2T FID 





46 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


it is clearly very desirable to supplement them with a 
few well-chosen full-scale tests. 

In general, the way in which the various parameters 
should be scaled can be deduced from the principles 
of dimensional analysis . 103 A more rigorous proce¬ 
dure requires a complete knowledge of the differential 
equations of motion of the system. Frequently it is 
not possible to scale properly every parameter or vari¬ 
able which occurs in the equations. Alien, for example, 
parameters such as gravity and density occur in the 
equations, rigorous scaling may not be possible or may 
be impractical to carry out experimentally. 

In constructing a model, a great amount of knowl¬ 
edge and judgment must go into the design and into 
the decision as to which features of the structure are 
the essential ones. Thus, it may be important that the 
moments of inertia of certain members be accurately 
reproduced although it may not be necessary to re¬ 
produce the exact shape. On the other hand, it is not 
sufficient that the structure have the same static 
strength as the prototype because one is interested 
here in dynamic effects where the inertia of various 
members may be very important in determining their 
resistance to damage. The degree of perfection with 
which certain components of the model are fabricated 
may or may not be vital. Thus, in tests made at 
UERL on simple cylinders, it was found that the 
ability of these structures to withstand explosive at¬ 
tack was critically dependent on the degree of round¬ 
ness of the cylinder, (see Section 1.3.4). A flat spot 
deviating from a perfect circle by as much as half the 
thickness of the material caused a definite weakening 
of the structure. On the other hand, this effect was 
not nearly so pronounced when the cylinders were 
ribbed in closer imitation to the construction of a 
submarine. 

The influence of the effect of strain rate on the 
strength of the materials needs to be studied further 
in connection with the use of models. If it were not 
for this effect , 104 it would be expected that the Hop- 
kinson law of scaling described in Section 1.2.4 should 
hold for shock-wave damage. Limited experiments at 
UERL on copper diaphragms of two sizes showed 
close agreement with the Hopkinson scaling law, in 
spite of the well-known rate of strain effect on the 
strength of copper. (See Chapter 12 .) This may be a 
result of the fact that at both scales the rate of strain 
was fairly high and in a region where the strength is 
not changing rapidly with rate of strain although it 
differs materially from the static strength. Extrapol¬ 
ation of this scaled result to much larger structures 


might be slightly in error because of the strain rate 
effect. This rate of strain difficulty does not, however, 
invalidate relative experiments in which various vari¬ 
ables such as method of construction of the model, 
distance of the charge, type of explosive, are com¬ 
pared at the same scale. The relative ease with which 
large numbers of experiments may be conducted with 
small-scale structures argues strongly in favor of the 
use of small models, or simple idealized targets, in the 
investigation of the fundamental nature of the dam¬ 
age process. 

134 Explosive Damage to Steel 

Cylindrical Shells 

Another type of simple system which has been stud¬ 
ied extensively, both experimentally and theoretically, 
is the air-filled cylinder. Various models of such cyl¬ 
inders were designed and studied at UERL. These 
were roughly scaled to represent a section of a sub¬ 
marine hull between bulkheads and were constructed 
with or without internal ring supports analogous to 
the stiffener ribs of a submarine. The sizes were ap¬ 
proximately one-tenth or one-twentieth of full scale 
in linear dimensions. A technique was evolved for 
rolling and fastening the cylindrical wall so that the 
maximum deviations from perfect circular cross sec¬ 
tion could be made as low as one-eighth of the wall 
thickness. 

Cylindrical Models without Internal 
Ring Supports 

The majority of the experiments with this type of 
cylinder were conducted with a model having a di¬ 
ameter of 5 % 6 in., an unsupported length of 8 V 2 
in. and wall thickness of 0.038 in. The ends, which 
consisted of circular steel plates 1 in. thick, were free 
to move inward on a central supporting rod as the 
cylinder was damaged . 33 These shells had a single 
longitudinal welded seam. In practice the charge was 
oriented relative to the cylinder so that the seam was 
on the far side of the cylinder, thereby minimizing 
the effect of unavoidable imperfections introduced by 
the welding. 

One interesting series of experiments with this 
model consisted of damaging the cylinders with 25 
grams of tetryl at various shallow depths. The results 
indicated that under certain conditions the bubble 
pulse may contribute greatly to the damage. This is 
illustrated by the photographs in Figure 19. All three 
cylinders shown were damaged with the same size of 
charge and at the same charge-to-cylinder distance 



DAMAGE PRODUCED BY UNDERWATER EXPLOSIONS 


47 




Figure 19. Photographs of cylindrical models showing effect of bubble damage in shallow water. 




































48 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


of 26 in. and with the charge vertically above the cyl¬ 
inder. They differed only in the depth of submergence 
of the charge-cylinder combination. In the first photo¬ 
graph, the charge was 1 ft beneath the surface so that 
the explosion bubble was vented before it could have 
emitted anything but the shock wave. Note the small 
amount of damage which is presumably the effect of 
the shock wave alone. In the third photograph, the 
system was submerged so that the charge depth was 
5 ft. Hence the normal bubble pulse would develop, 
largely uninfluenced by the presence of the surface. 
The damage is considerably larger. In the second pho¬ 
tograph, the depth of submergence of the charge was 
2 ft, which presumably led to the bubble being re¬ 
pelled by the surface so that the bubble pulse came 
from a point practically in contact with the cylinder, 
resulting in its complete destruction. It is important 
to emphasize that the downward migration of the 
bubble due to free surface repulsion, observable with 
small charges, does not occur with charges greater 
than several pounds. This is a consequence of the rela¬ 
tively greater upward force of gravity on the larger 
gas globe. This is an example of a phenomenon which 
is not easily scalable, and illustrates the fact that ex¬ 
treme care must be exercised in the design and inter¬ 
pretation of model scale experiments. 

Another series of experiments was designed to in¬ 
vestigate the effect of slight deviations from a perfect 
circular cross section of the cylinder wall. This was 
accomplished by deforming the shell before mounting 
so that the curvature in certain local regions was al¬ 
tered. Deviations from a perfect circular cross section 
of V 2 - to 2-wall thicknesses did not greatly affect the 
extent of the damage in shallow water, but were im¬ 
portant factors in determining the locations of the 
damage. In deep water, however, where a considerable 
hydrostatic load was superimposed on the explosive 
loading, these slight imperfections in the cylinder 
wall significantly increased the observed damage. 

Cylindrical Shells with Internal 
Ring Supports 

Later investigations were conducted with cvlinders 

o %j 

which had internal stiffener rings and the following 
dimensions: diameter 8% in., length 8*4 in., and 
wall thickness 0.038 in. The stiffener ribs were of 
strength and at spacings appropriate to a scaled model 
of a submarine pressure hull. In shallow water experi¬ 
ments with these models, bubble pulse damage and 
the influence of imperfections were observed but 


found to be less severe than in the case of the un¬ 
ribbed cylinder. To study the effect of a super¬ 
imposed hydrostatic load, the damage to cylinders of 
this model by 25-gram tetryl charges at various dis¬ 
tances was determined at depths extending to TOO ft. 
The results are presented in Figure 20, in which the 
charge-to-cylinder distance at which a certain arbi- 


800 


700 


600 


500 


— 400 


CL 

UJ 


200 


I 0 Or 





/ 

/ 

/ 

/ 




/ 

/ 

/ 

* 





7 

/ 

/ 





/ 

/ 






1 

1 






/ / 

/ / 

/ / 






/ 

1 / 





/ 

/ 

/ 






10 20 30 40 50 60 


CHARGE DISTANCE (INCHES) FOR CRITICAL DAMAGE 

Figure 20. Plot of charge distance required to produce 
critical damage versus depth. 


trarily defined “critical” damage was inflicted by the 
explosion is plotted against the depth of submer¬ 
gence. 105 

In order to distinguish between shock-wave damage 
and bubble-pulse damage to the ribbed cylinders, high¬ 
speed motion pictures (2,500 frames per sec) of the 
cylinder at the time of the explosion were taken. Such 
pictures were obtained for a number of different 
depths extending to TOO ft. Photographs for one test 
are shown in Figure 12 and have been referred to in 
a previous section. O 11 the basis of a number of similar 
photographs obtained at other depths, there seems to 
be little doubt that with hydrostatic loading of the 
model an appreciable amount of additional damage 
is caused by the bubble pulse, apart from the damage 
caused by the shock wave. 



















EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


49 


Theoretical Treatment of Static and Dynamic 
Buckling of Cylinders 

Tn conjunction with the experimental work on cyl¬ 
inder models at UERL, theoretical studies were car¬ 
ried out at Cornell. One result of these investigations 
was a revision of the theory of the static strength of 
cylindrical shells under hydrostatic pressure. An error 
was found in Love’s fundamental theory of elasticity 
and an entirely new method of solving the equations 
of the resistance of a cylindrical shell was carried 
through to completion. The results were expressed in 
the form of tables which should be useful to submarine 
designers or designers of other externally loaded 
pressure vessels. 100 

At the same time, a beginning was made on the 
problem of the dynamic resistance of cylindrical shells 
to explosive loading. 107 From the results of this 
theory it would appear that pressures considerably 
greater than the static buckling pressures are required 
to initiate buckling for dynamic loading such as oc¬ 
curs with a decaying shock wave. Moreover, on the 
basis of the theory, one would not expect a superim¬ 
posed hydrostatic load to effect the results to the ex¬ 
tent indicated by experiment. (See Figure 20.) The 
reason for this discrepancy is not yet clear. 

The theoretical treatment of explosive damage to 
cylindrical shells is much more difficult than is that 
of the circular diaphragm. One difficulty arises be¬ 
cause of the instability of the cylinder shape. Once 
an indentation is produced, there is a tendency for 
collapse to occur because of the hydrostatic pressure 
alone. 

13 5 Results of Other Damage Tests 

Countermining of Horn Mines 

Tests were conducted at L T ERL with some Japa¬ 
nese anti boat horn mines, as well as with some replica 
horns manufactured b} T the Gulf Research and Devel¬ 
opment Company, to determine the optimum condi¬ 
tions for countermining such mines in shallow 
water. 108 Sufficient damage must be caused by the 
countermining charge to damage a lead cylinder and 
crush an inner acid-containing glass vial. The damage 
process of the horns was such that the peak pressure 
of the shock wave was the important factor; the pres¬ 
sure necessary to activate the horn was found to be 
approximately 1,500 psi. Thus for a 30-lb charge in 
a depth of water of 5 ft the effective countermining 
radius for 50 per cent activation was 37 ft. Experi¬ 
ence has shown that under the same conditions activa¬ 


tion of all the mines would be reasonably certain at 
27 ft or less. Supplementary work has shown that it 
is not likely that such a mine as the Japanese anti¬ 
boat mine will be countermined by sympathetic de¬ 
tonation at distances as great as the distance at which 
it can be countermined through operation of the horn. 

Improbability of Underwater Sympathetic 
Detonation 

In general it is difficult to detonate underwater 
charges of the common explosives fillings or even 
booster charges, by the explosion of another charge. 
Thus in one series of tests, 109 small bare (but water¬ 
proofed) tetryl and TNT charges failed to detonate 
when as close as 5 ft from a 100-lb TNT charge. An¬ 
other test 1Gb consisted of four trials, in each of which 
an unfused TNT-loaded GP bomb was placed nose 
to nose 4 ft from a Mark 13 mine loaded with 700 lb 
of torpex. In each case the explosion of the Mark 13 
mine failed to detonate the charge of the GP bomb. 
On the other hand, the most sensitive detonator cap 
tested (U.S. Army Corps of Engineers special blasting 
cap, nonelectric) was sympathetically detonated when 
at a distance as great as 29 ft from the explosion of 
100 lb of TNT. 109 In countermining actual under¬ 
water weapons, other factors, such as damaging or ac¬ 
tivating specific fuze mechanisms, must be considered. 
In the absence of any mechanism which can be acti¬ 
vated by the shock wave it is unlikely that the explo¬ 
sive charge in such weapons can be detonated sym¬ 
pathetically. 

If an occasion requires the detonation of a charge or 
charges following the explosion of a given charge, it is 
necessary to provide a mechanical firing mechanism 
which is activated by the shock wave from the given 
charge. Tests on one such device in shallow water at 
Woods Hole revealed an interesting dependence of the 
range at which it would respond on the nature of the 
bottom (hard sand or soft mud). It would be impor¬ 
tant to study piezoelectrically the nature of shock- 
wave transmission under these conditions. 

1.4 EXPERIMENTAL METHODS FOR 

STUDYING UNDERWATER EXPLOSION 

PHENOMENA 

141 Piezoelectrical and Other 

Electrical Methods 

Piezoelectric Pressure Gauges 

In making an experimental study of underwater 
explosions, it is obviously important to devise meth- 





50 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


ods of determining the pressure in the shock wave at 
various locations around the explosion, preferably as 
a function of the time. It was early suggested by 
J. J. Thompson in England that piezoelectric crystals 
could be used to measure these very short-time phe¬ 
nomena. The British developed, after World War I, 
a large gauge made from a plate of tourmaline. This 
is a naturally occurring crystal which is piezoelectri- 
cally active, that is, when subjected to pressure an 
electric charge appears on the surfaces which can be 
measured by electrical instruments. Their large Brit- 
ish tourmaline gauges were utilized in some extremely 
interesting investigations which served to outline the 
nature of the phenomena and the problems yet to 
be solved. 110 As the technique of using oscillographic 
equipment and vacuum-tube amplifiers progressed, it 
became clear that the gauge could be further im¬ 
proved. In the first place, it was desirable that it be 
made physically small because otherwise the time 
required for the wave to pass by the gauge was an 
appreciable fraction of the duration of the phenomena 
being studied. Furthermore, a great increase in the 
ruggedness of the gauge was necessary if the pressure 
near to charges was to be explored. These ideas led 
naturally to the development of very small tourmaline 
gauges consisting essentially of one or more small 
slabs of crystal with metallic coating on the appro¬ 
priate faces connected to a cable, the whole unit being 
then insulated and waterproofed. Figure 21 gives a 
diagram of one of the latest models of underwater 
tourmaline pressure gauges. The size usually used for 
studying the shock wave from actual service weapons 
is about V 2 in. in diameter. It was possible with these 
gauges to measure the shock wave reasonably close to 
the charge without losing the gauge. Thus, it was 
routine to place them 20 ft from a 300-lb depth 
charge where the pressure was about 6.000 psi. 
Pressures as high as 30,000 psi have been reliably 
measured. 

Many hundreds of these units were made by the 
Stanolind Oil and Gas Company [SOG], a contractor 
to Division 2, by the Beeves Sound Laboratory, a sub¬ 
contractor to the Oceanographic Institution, and by 
the staff at UEBL itself. These sources supplied 
gauges to many other laboratories. They were used 
daily for the routine comparisons of different explo¬ 
sive compositions and for other studies at scales rang¬ 
ing from a few grams to hundreds of pounds of ex¬ 
plosive. A complete description of their construction 
and use is available. 61,111,112 

In order that a piezoelectric gauge may be used for 


absolute pressure measurements it is necessary to 
calibrate the gauge. This is usually accomplished by 
measuring the charge generated by the gauge when 
it is subjected to a known change in pressure in a 
compression chamber which is filled with a suitable 


/EXPANDED 
TYPICAL 
CONNECTION 


I 

P 

s 

S, 

T 

w 



CURED LATEX INSULATION + 
STEEL PLATE 
DUPONT SILVER ELECTRODE 
HANOVIA SILVER SHIELD 
TOURMALINE DISCS 
WIRING POSITIVE 


EXPANDED SECTION A-A 

(ELECTRODE FACES SWEATED 
TOGETHER) 


W, -WIRING NEGATIVE 


Figure 21. Schematic drawing showing dimensions and 
construction of tourmaline piezoelectric gauge. 


liquid. The change in pressure in the calibration 
chamber is usually brought about by opening a needle 
valve when the chamber is under a known pressure, 
or by bursting a diaphragm covering an opening in 
the chamber. The main difficulty with this so-called 
static method is that the change in pressure cannot be 
made to take place sufficiently rapidly to compare 
with the very short time of rise of pressure which 
occurs in the shock wave. It is also not known to what 
extent reflections and oscillations in the pressure 
chamber may affect the results. Mounting of the gauge 
in the pressure chamber presents another problem. 
If the crystal element alone is mounted in the pres¬ 
sure chamber, it is not definitely known whether a 
calibration of this type will be the same after the 
crystal element is mounted on a cable and the whole 
assembly is waterproofed. When the completed gauge 
is to be calibrated, the gauge must be mounted in the 


l"\| ii'KVn A i. 















































































EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


51 


chamber through a gland nut on the gauge cable, a 
procedure which was found under certain conditions 
to give rise to spurious electric charge. In view of 
these problems independent methods of pressure mea¬ 
surements which would serve as a check on the piezo¬ 
electric gauge calibration were carried out, the results 
of which are mentioned in Section 1.2.12. On the 
basis of these results, together with a detailed study 
of the static calibration method, it was concluded that 
the static calibration of the tourmaline piezoelectric 
gauges, when carried out with the proper precautions, 
is adequate for most ordinary explosives work. 

Tourmaline has a particular advantage among the 
various available crystals which show the piezoelectric 
effect in that it produces an electric charge when sub¬ 
jected to a hydrostatic pressure, that is, a pressure 
uniformly applied to all surfaces, whereas, most of 
the other materials commonly employed will show a 
charge only when they are compressed in one direc¬ 
tion alone. Thus, quartz, Rochelle salt, and ammoni¬ 
um dihydrogen phosphate, a new material known as 
ADP, have been used for pressure gauges for under¬ 
water use but in each case they require a container 
designed to protect the edges of the crystal from the 
pressure. This makes the gauge more complicated and 
especially makes it more difficult to secure the high- 
frequency response that is necessary in order to record 
faithfully very short-time phenomena. Nevertheless, 
Rochelle salt and the ADP crystals have certain ad¬ 
vantages, primarily their very much greater sensitiv¬ 
ity. Rochelle salt in particular is 100 times as sensi¬ 
tive as tourmaline or quartz but has a very serious 
drawback in that it is highly temperature-sensitive 
so that it is very difficult to use it for quantitative 
measurements. Furthermore, the crystal is fragile and 
seriously affected by moisture. ADP is somewhat less 
sensitive than Rochelle salt, is less affected by tem¬ 
perature but is also fragile and moisture-susceptible. 
It proved to be quite convenient, however, for sound 
ranging setups where a more sensitive pickup was 
desired. The Road Research Laboratory [RRL] in 
Great Britain has successfully used quartz gauges for 
underwater work. Quartz would seem to have little 
advantage over tourmaline, since it is no more sensi¬ 
tive and requires a container. 

Other Electrical Pressure Gauges 

Early in World War II, considerable experimenta¬ 
tion was carried out, especially by DTMB, on resis¬ 
tance-type pressure gauges. 113 The simplest form for 
this is a small radio resistor. The applied pressure of 


the shock wave compresses the resistance element and 
thereby changes its resistance by a small amount. 
These have an advantage over the piezo gauges in 
that they are of low impedance, whereas the crystal 
gauges are of very high impedance, and thus subject 
to the difficulties associated with high-impedance cir¬ 
cuits. On the other hand, the resistance gauges which 
were tried were not very successful, partly because of 
their very low sensitivity which meant that an am¬ 
plifier of very great gain was necessary. Another dif¬ 
ficulty was the fragility of all those gauges which 
were tried and the fact that many of them showed 
hysteresis, that is to say, they did not come back to 
their original state after having been compressed. It 
is still not at all certain that further research could 
not develop a successful underwater resistance-type 
gauge. 

In principle, it should be possible to make success¬ 
ful underwater pressure gauges using the condenser- 
microphone principle or the magnetostrietive prin¬ 
ciple. The latter effect was successfully used in under¬ 
water microphones but no effort was apparently made 
to adapt them to the high pressure and short dura¬ 
tions encountered in shock waves. This could prob¬ 
ably be done and might yield a gauge with many 
advantages. 

Another principle partially investigated is based on 
the dependence of the conductance of sea water itself 
on pressure. The David Taylor Model Basin initiated 
some investigations at Catholic University on the 
effect of pressure and temperature on the conductivity 
of sea water but practical gauges were never developed. 
This is a promising principle and probably should be 
followed up. 

Recording Methods for Electric 
Pressure Gauges 

Since the tourmaline gauges are almost the only 
ones successfully used in this country, a brief descrip¬ 
tion of the other components necessary for their em¬ 
ployment will be given. 114 These additional compo¬ 
nents would not be greatly different for the other 
types of gauges but some modifications would be 
required. 

The first problem is that of a suitable cable for 
transmitting the electric impulses from the crystal to 
the recording equipment. This proved to be a very 
difficult problem because ordinary rubber cables, for 
example, give rise to a signal themselves when com¬ 
pressed by the pressure wave. Furthermore, it is neces¬ 
sary that the cable be mechanically strong since it is 







52 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


roughly handled in use and by the explosion. Its 
capacity and insulation resistance must be of the 
right magnitude and stable with time and treatment. 
Cables were finally found which satisfied all these 
requirements. Especially successful was the cable de¬ 
veloped at DTMB which employed copper tubing as 
the outside shield. 115 Much thought was put into the 
problem of terminating the cable properly so that a 
length of, say, 600 ft would transmit faithfully the 
signal produced by the gauges. This involved the de¬ 
sign of terminating networks which not only com¬ 
pensated for electric reflection at the ends of the 
cable but also minimized the distortions due to the 
dielectric absorptions of the cable insulation. This 
problem was quite successfully solved. 116 It is also 
necessary to have suitable vacuum-tube amplifiers 
with a broad range of frequency response, sufficient 
gain, high stability and reproducibility, and a linear 
response with amplitude. These were obtained by 
making small modifications of commercially available 
equipment. 114 The output of such an amplifier was 
fed into a cathode-ray oscillograph [CEO] tube which 
was equipped with an electronic time base so that 
the spot of the oscillograph swept across the screen 
horizontally with time and was deflected upward pro¬ 
portionately to the applied pressure. This trace was 
then photographed, with the result that the pressure 
as a function of time was permanently recorded. (See 
Figure 1.) In some cases, rotating drum cameras were 
used so that the motion of the film provided the time 
axis. Naturally, other auxiliary circuits such as oscil¬ 
lators for putting on timing marks to measure the 
time scale, calibration equipment for putting ampli¬ 
tude marks so that the pressure could be determined 
numerically, and test equipment were also necessary. 
With the total equipment in use for some time before 
the end of World War II, it was possible to make 
routine daily measurements on charges of a great 
range of sizes which were accurate to within perhaps 
3 per cent as far as peak pressure was concerned. 
Furthermore, impulse measurements to better than 
5 per cent and energy measurements to better than 7 
or 8 per cent could be made. Many thousands of such 
records were taken at TTERL during World War II. 

A background of four years’ experience in design 
and construction of instruments for recording explo¬ 
sion pressure-time curves in the field has shown the 
importance of factors which are of less concern in 
laboratory work. These considerations are doubtless 
familiar enough to all who have made such measure¬ 
ments, but the following discussion is included as a 


possible help to those who may be called upon to plan 
equipment for field tests. 

Field measurements of underwater explosions must 
frequently be made under adverse conditions, both for 
the operator and for the equipment. Therefore, it is 
important that the equipment function properly under 
unfavorable combinations of temperature, humidity, 
and primary power-supply variations. For the sake of 
the operator, it is also important that the necessary 
controls be simple and straightforward, and that 
proper functioning of the equipment be easily deter¬ 
minable. The possible need for repair in the field with 
limited facilities should also be taken into account. 

A particularly important consideration is the fact 
that explosions occur once and may involve consider¬ 
able amounts of time, effort, and money. In these 
circumstances, equipment which fails an appreciable 
fraction of the time may be worse than useless. 

These difficulties of field work underline the im¬ 
portance of mutual understanding on the part of the 
man who develops the equipment and the man who 
uses it. The former should know what will be required 
of the equipment and should have field experience; 
the operator should have some knowledge of the basic 
principles of the equipment in order to use it intel¬ 
ligently. When a new type of measurement is to be 
undertaken, the design of needed electronic equipment 
must be based on knowledge of field requirements and 
what is reasonably possible. 

The actual design should then be developed to 
meet the requirements with a minimum of adjust¬ 
ments and a maximum of reliability. Large safety 
factors should be allowed, to take account of such 
things as tube variations, tolerances of component 
parts, and leakage currents. Good mechanical layout 
and construction and clean wiring may mean the dif¬ 
ference between servicing in the field and stopping 
work until laboratory repairs can be made. It is also 
worth while to use standard and readily available 
components as far as possible. 

The completed instrument should be tested under 
actual or simulated conditions and these results kept 
recorded on the instrument as a part of the service 
record. Routine tests and inspections of all equipment 
are valuable in maintaining it at peak performance 
and avoiding breakdown. 

1,42 Mechanical Gauges 

The piezoelectric gauges described above were in¬ 
dispensable for an accurate picture of the pressure 
as a function of the time where it was desired and 





EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


53 


they were entirely practical for a wide range of uses. 
However, especially in the early days of their develop¬ 
ment and for many special applications even now, the 
necessity for long cables and electric equipment on 
shipboard made it desirable to have mechanical gauges 
which, with proper understanding of the theory of 
their response, enabled certain properties of the shock 
wave to be measured. Historically, the mechanical 
gauges were developed before the electric ones, though 
much of their theory was not known until later. 

The Ball Crusher Gauge 

Probably the most successful mechanical gauge is 
the so-called ball crusher gauge developed by NOL. 117 
Figure 22 shows the construction of this simple gauge 



CAP AND PISTON AND COPPER ANVIL AND 


PISTON GUIDE SPRING BALL BASE 

Figure 22. Construction of ball crusher gauge. 

which, it is seen, consists of a copper ball held between 
an anvil and a light piston. The pressure wave, reach¬ 
ing the gauge, pushes the piston against the ball thus 
flattening it on two sides. The extent of the depression 
is measured and from it the peak pressure in the wave 
can be determined, provided some estimate of the 
duration of the pressure pulse is known. The ball 
crusher gauge, like all mechanical gauges, does not 
have a quick enough response time to measure peak 
pressure directly without further consideration. The 
static pressure required to produce a given deforma¬ 
tion on the copper sphere can be measured but this 
cannot be converted directly into peak pressure in the 
shock wave without two corrections. In the first place, 
there is a correction of approximately 20 per cent due 
to the increased strength of the copper balls at high 
rates of strain such as encountered in exposure to a 
shock wave. 104,118,119 (See Chapter 12.) Another 
factor affecting the conversion of ball deformation 
to peak pressure is the inertia of the piston. Because 
of this inertia, the standard NOL gauge really re¬ 
sponds to a combination of peak pressure and the rate 
of decay in the first 60 or 70 /xsec of the shock wave. 
It will thus not register the same deformation and, 


therefore, not the same apparent pressure for 5,000-psi 
peak pressure from a small charge as for 5,000-psi 
peak pressure from a large charge unless this time 
factor is taken into account. Fortunately, the correc¬ 
tion is not too critical provided the charge is of the 
order of the size of service weapons or larger and the 
theory is adequate to take care of the difference. 120 
Therefore, when properly interpreted, ball crusher 
gauges can be used to give peak-pressure values re¬ 
producible to 2 or 3 per cent for the shock wave of 
a large charge. It is, however, necessary to be sure 
that the wave is not complicated by multiple peaks as 
is sometimes the case, especially off the end of the 
charge. It is this uncertainty of the form of the 
pressure-time curve from special situations that makes 
it highly desirable to have electric gauges in conjunc¬ 
tion with the mechanical gauges. The ball crusher 
gauge is very convenient to use since it is self- 
contained, small, and easily read. 

Theory of the Ball Crusher Gauge 

The response of the ball crusher gauge to an explo¬ 
sion shock wave can be treated mathematically by 
simply applying Newtoids laws to the motion of the 
movable piston. 121 ’ 122 The effective mass of the pis¬ 
ton includes small correction factors for the mass of 
the copper sphere and for the mass of the water follow¬ 
ing the piston. The force acting on the piston is ex¬ 
pressed in two terms. One term, AP m e~ t/6 represents 
the force exerted by the shock wave on the piston of 
area A as a function of time. (See Section 1.2.4.) The 
other force term, A.r, represents the resistance of the 
copper ball to plastic deformation. This has been 
found to be linear over a wide range of deformation, 
and A, the proportionality factor which gives the 
force as a function of the piston displacement x, 
should be determined by appropriate calibration for 
each production lot of annealed copper spheres. 

The spheres may be calibrated statically or dynam¬ 
ically. Since they are deformed at high rates of strain 
by the shock wave, it is necessary to apply a correction 
factor of about 20 per cent in case static calibrations 
are employed, i.e., the proportionality factor A should 
be increased by 20 per cent over that determined 
statically. At UERL a dynamic calibration was em¬ 
ployed in which the factor A was computed from the 
deformation produced by a free falling weight which 
struck the sphere with known energy. 123,124 In this 
case the rate of strain effect is assumed to be the same 
as that encountered in the use of the gauge. 

The solution of the differential equation of motion 














54 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


for the piston is relatively simple. The ball deforma¬ 
tion corresponds to the maximum value of the piston 
displacement. This maximum is reached in 160 or 
170 /xsec in the standard NOL gauge (effective piston 
mass about 16 grams, with %-in. copper spheres). 
Since the decay of the shock wave may be appreciable 
during this time, especially for small charges, the de¬ 
formation does not directly yield an estimate of peak 
pressure. Fortunately, the theory gives quantitatively 
the relation between deformation, peak pressure, and 
time constant so that true peak pressures can be com¬ 
puted from the deformations provided an estimate of 
0, the time constant, is available. The dependence 
on 0 becomes very small for large charges such as 
service weapons, for which the decay in pressure is 
small over the period of response of the gauge, so that 
the ball crusher gauge acts very nearly as a direct 
peak-pressure gauge under these conditions (6 170 

/xsec.) It is, of course, necessary to remember that the 
simple form of the theory mentioned here assumes 
exponential decay of the shock wave. If the shock 
wave form is complicated (as it is off the ends of some 
service weapons) 9113 ’ 125 the interpretation of the gauge 
readings becomes considerably more complicated. 126 

Diaphragm Gauges 


lb or greater and is quite convenient for relative mea¬ 
surements such as in the comparison of explosives. 

A similar gauge was developed at the Explosives 
Research Laboratory of Division 8 128 and widely util¬ 
ized at UERL. 15 This gauge consists of a cylindrical 
steel box with a steel diaphragm clamped over its 
front opening. (See Figure 24.) The pressure wave 
dishes the diaphragm and the central deflection is 
measured. For quite small charges of the order of a 
pound or so (0 = 60 /xsec), this gauge seems to meas¬ 
ure a quantity moderately closely proportional to 
the impulse in the wave but with charges of 300 lb 


FLANGE. 




Another simple type of mechanical gauge is the so- 
called Modugno gauge, 127 which consists of a copper 
diaphragm about 1% in. in diameter clamped over a 
small air space. (See Figure 23.) The pressure wave 



Figure 23. The Modugno gauge. 


Figure 24. Assembly of underwater steel diaphragm 
gauge. 

or greater (0 = 500 ^sec), it appears to be, both theo¬ 
retically and experimentally, essentially a peak- 
pressure gauge, since the deflection time is of the 
order of 170 g?ee. It is more reproducible when prop¬ 
erly employed but not quite so convenient as the ball 
crusher and the Modugno gauges because of its larger 
size and weight. Because of its simplicity, however, 
in addition to its usefulness for measuring the relative 
effectiveness of different explosives, it proved to be a 
convenient gauge for experimental studies of the more 
fundamental properties of underwater explosions 
which are important in damage to steel plates. These 
studies, theoretical as well as experimental, were men¬ 
tioned in Section 1.3.2. 


dishes in the soft copper diaphragm and the deforma¬ 
tion can easily be measured. This deformation is quite 
reproducible but is not simply related to the applied 
pressure. In other words, the static pressure required 
to produce a given deformation is not simply related 
to the dynamic peak pressure which produces the 
same deformation. The gauge is, however, essentially 
a peak pressure gauge for charges of the order of 300 


Pistox-Type Momentum Gauges 

When used with large charges, all of the above men¬ 
tioned gauges give an indication of the peak pressure. 
It is very desirable to have a mechanical gauge which 
can measure the impulse in the wave since impulse, 
under certain conditions, is a more important quan¬ 
tity than peak pressure in so far as damage is con¬ 
cerned. Hilliar in Great Britain developed such a 







EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


55 


gauge just after World War I. 129 This gauge consists 
of a steel block with a long cylindrical hole. In the 
hole is a copper crusher cylinder such as used in gun 
gauges, and a steel piston. It differs from the ball 
pressure gauge in that the piston has considerable 
mass and length. Figure 25 shows the construction of 
one of these piston-type gauges. Since the piston is 


the same principle. The theory of piston gauges has 
been treated in some detail recently. 130 

The results of all types of pressure gauges are in¬ 
fluenced by the way in which they are mounted and 
by the surroundings. Thus a gauge mounted in a 
large and very thick steel baffle will read approxi¬ 
mately double the peak pressure which will be mea- 



BODY 

CAP RINGS 


VVVV VVV11 


AAAA/VVVH 


ASSEMBLED 

GAUGE 


ANVILS, SPRINGS, COPPER CYLINDERS, 

PISTONS 


Figure 25. Assembly of Hilliar gauge. 


reasonably heavy, it takes a certain amount of time 
to accelerate. There is a gap between the end of the 
piston and the copper crusher so that the piston can 
accumulate momentum before striking the copper 
cylinder. By making certain simplifying assumptions, 
the mathematical treatment of this system is not diffi¬ 
cult and shows that the deformation of the copper 
crusher cylinder can be interpreted in terms of the 
impulse in the shock wave up to a certain time. By 
having a number of these gauges with different piston 
masses and length of travel it is possible to block out, 
roughly, the form of the pressure-time curve by means 
of purely mechanical instruments. This gauge was 
used very successfully by Hilliar. However, it requires 
extremely careful handling and has not been so suc¬ 
cessful in the hands of investigators during W T orld 
War II as it was with Hilliar. Nevertheless, it is a 
useful instrument. A number of variations on this 
design have been made but they all utilize essentially 


sured by a gauge in free water. This is because of the 
doubling of the pressure by the superposition of the 
incident and reflected waves. However, the baffle has 
to be 3 or -I ft thick before this effect is detected by 
most mechanical gauges because these instruments 
require a certain finite time to operate and this time 
must be small compared with the travel time of the 
wave back and forth through the steel baffle. Gauges 
are also affected by their orientation relative to the 
oncoming wave. It is customary to use the mechanical 
gauges described above face-on to the explosion, except 
Hilliar and momentum gauges. The amount of inertia 
attached to the gauge, i.e., the massiveness of its 
mounting, has been found to be relatively unimpor¬ 
tant. This has some influence on the results but for¬ 
tunately the ball crusher gauges, at any rate, seem to 
function quite reproducibly with very little backing. 
In all cases it is desirable to mount the gauges as far 
from reflecting obstacles as possible. This is particu- 


tQKi'IBENTIAL l 






















56 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


larly true of the piezoelectric gauges which are capa¬ 
ble of yielding the complete pressure-time curve. 
Nearby solid objects will reflect portions of the wave 
striking them and these reflections will be picked up 
by the piezo gauges. It is definitely had to use wood 
for mounting any type of underwater pressure 
gauge. 131 Apparently this low density, soft material 
reflects a rarefaction wave and serious errors may be 
obtained if the pieces of wood are placed near any of 
the above gauges. 

143 Photographic Methods 

One of the most interesting and fruitful techniques 
for the study of underwater explosion phenomena is 
that of photography. Several photographic methods 
have been developed by means of which there have 
been obtained detailed pictures of a number of the 
phenomena which occur in connection with these ex¬ 
plosions. 

Flash Charge Photography 

One of the most useful devices was the invention 
at the Explosives Research Laboratory of Division 
8 of the explosive flash bulb. This source of illumina¬ 
tion can be made to give a very bright flash of light 
lasting only a few /usee, which is a sufficiently short 
time to “stop” the shock wave in its rapid motion. 
This flash bulb consists of a spherical charge of high 
explosive surrounded by a very thin layer of argon gas 
in a transparent container. The explosive is detonated 
from its center by means of a Primacord fuze. There- 

*j 

fore, the detonation wave should reach all points of 
the surface of the sphere simultaneously, sending a 
shock wave through the argon gas. This shock wave 
heats the gas to an extremely high temperature and 
causes it to emit a flash of light. The duration is short 
because the time required for the shock wave to pass 
through the gas is very short. Synchronization of the 
firing of the flash lamp and the phenomenon to be 
studied is readily accomplished by means of the Pri¬ 
macord fuze. The flash charge and the charge being 
studied are both connected by predetermined lengths 
of Primacord to the same detonator cap, so as to ex¬ 
plode the two charges at the proper time interval. 
Standard cameras can be utilized provided they are 
contained in a strong metal cylinder with a thick glass 
window to protect them from the explosions. Simple 
relays may be used to open the shutter before the event 
and close it shortly thereafter. Details of these tech¬ 
niques have been described elsewhere. 13 (See also 
Division 8, STP.) 



Figure 26. Flash photograph showing shock wave and gas 
bubble of long cylindrical charge detonated at one end. 



Figure 27. Flash photograph of 3 3 8 -in. equilateral cast 
pentolite cone detonated at apex. 


rOXFlDKKTlAll 
















EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


57 


Figure 2 (Section 1.2.4) shows an underwater ex¬ 
plosion at a time when the bubble has expanded to a 
radius of about three times the radius of the original 
charge. The photograph shows clearly the outline of 
the original charge because enough light was emitted 
by its detonation to record its shape on the film. Later, 
when the flash charge was fired, the outline of the 
bubble and the silhouette of the shock wave were re¬ 
corded. The shock-wave surface is quite smooth, which 
is also to be expected theoretically since any irregu¬ 
larities should rapidly smooth themselves out. Notice 
also that the bubble surface does not show pronounced 
irregularities. 

The shape of the shock wave about the charge re¬ 
flects the shape of the charge. Spherical charges (see 
Figure 2 and Figure 3, Section 1.2.4) give spherical 
shock waves, whereas elongated shapes (Figure 26) 
give distorted ellipsoidal shock waves with this broad 
end at the cap end of the explosive. Figure 27 shows 
a photograph of a conical charge detonated at the 
apex. 

An example of the use of photographic techniques 
for quantitative studies is the evaluation of shock- 
wave parameters by the so-called optical distortion 
method. 132,133 Figure 28 shows the apparent distor¬ 
tion of a grid ruled on a Lucite sheet as viewed 
through a spherical shock wave. Several variations of 
the experimental setup are possible, but in the case il¬ 
lustrated the grid is in a plane through the center ol: 
the shock-wave sphere. It is possible to develop a 
theory which relates the displacement of the grid in¬ 
tersections from where they would appear in the ab¬ 
sence of the shock wave (obtained by extrapolation of 
the lines outside the shock front) to the peak pressure 
and decay constant of the shock wave. A knowledge of 
the index of refraction of sea water as a function of 
pressure is required. It is necessary to design the ex¬ 
periment with great care so that all the distances and 
angles required in the theoretical analyses are known 
with sufficient precision. Results obtained by this 
method were quoted in Section 1.2.12. 

Another promising application of flash photo¬ 
graphic techniques involves a double exposure accom¬ 
plished by the use of two flash charges detonated a 
known interval of time apart. From the two shock- 
wave silhouettes on the resulting photograph the 
mean propagation velocity can be measured and hence 
the peak pressure in the shock wave can be derived 
(see Section 1.2.12). This method has been explored 
but has not as yet fully developed. 13 

An important series of studies on cavitation was 


carried out using underwater flash charge photo¬ 
graphy. Illustrations have already been given of the 
cavitation produced when a shock wave is reflected 
by a free surface and when a thin air-backed dia- 
phragm is damaged (Section 1.2.5, Figure 6 and 



Figure 28. Flash photograph of shock wave traversing 
ruled grid. 


Figure 11). Figure 29 shows the extent of the cavi- 
tated region under certain conditions of shock-wave 
attack on heavy free air-backed plates. In these cases, 
heavy steel disks were attached to air-filled pipe sec¬ 
tions of larger diameter by very thin diaphragms so 
that the resistance to displacement was essentially 
all from the inertia of the heavy disk, the strength 
of the thin diaphragm being negligible. The extent 
and shape of the cavitated regions correspond roughly 
to those computed from the results of the theoretical 
analysis of the systems. The theory takes into account 
the time variation of the pressure at any point in the 
water due to the incident pressure wave, the reflected 
waves from the accelerating disk, and the diffracted 
waves from regions around the target. 

The significance of these experiments is chiefly in 
the fact that they constitute an experimental verifi¬ 
cation of the essential correctness of the theory, 
including the effect of cavitation, for shock-wave 
interaction witli this simple type of target. It is char- 









58 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 



Figure 29. Flash photographs showing cavitation in front of rigid air-backed free plate. 


acteristic of the so-called fundamental approach to 
a problem that one should proceed step by step along 
a course of investigation in which general principles 
determining the phenomenon are postulated then 
tested under conditions which are as simple as pos¬ 
sible. In this way false starts may he eliminated more 
efficiently, and if one eventually establishes the fun¬ 
damental laws of nature which control the phenom¬ 
ena, the usually more complicated practical problems 
may then be attacked with confidence. 

Since the occurrence or nonoccurrence of cavitation 
has an importance in determining damage to targets 
or response of gauges, many photographs designed to 
detect cavitation were taken at LTERL. For example, 
cavitation was shown not to occur under the normal 
conditions of use of the mechanical gauges employed 
but was shown to occur when the cylindrical shell 
models were appreciably damaged. 

The use of flash charge photography to show the 
Mach phenomenon of shock wave interaction was 
mentioned in Section 1.2.5. 

High-Speed Motion Picture Photography 

In addition to the flash charge techniques for 
photographing underwater explosion phenomena, 


high-speed motion picture photography (100 to 3.000 
frames per sec) has been successfully used. This re¬ 
quires intense light sources which must have dura¬ 
tions at least as long as the phenomena being photo¬ 
graphed. For this purpose, ordinary photographic 
flash bulbs have been used, and some progress has been 
made in the development of a suitable underwater 
flare. To date, high-speed motion picture techniques 
have been used primarily to study explosive damage to 
underwater targets (see Figure 12, Section 1.3.4) and 
to study the behavior of the gas bubble. From these 
photographs, measurements of the bubble radius and 
the bubble migration can be made. 

As in the flash photography techniques, the camera 
is contained in a heavy watertight case equipped with 
a small window. In principle there is no limit to the 
size of charge which can be photographed, provided 
the water is of sufficient clarity and the lighting suffi¬ 
ciently intense. Considerable development has taken 
place to perfect intense underwater light sources and 
further developments are foreseen. However, the 
clarity of the water is a serious limitation since sea 
water, in general, is very turbid, and thus work with 
only very small charges can be carried out. Where 

*J cj 

larger charges or targets are to be photographed, the 















EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


59 


experiments must be carried out in localities where 
the sea water is sufficiently clear, for example, in the 
Gulf Stream, or near the Bahama Islands or Cuba. 
The Underwater Explosives Research Laboratory has 
sent expeditions for photography work into each of 
these locations. There are other localities where the 
water is sufficiently clear during certain seasons of 
the year. 

The photographic techniques for studying the dam¬ 
age process, as well as explosion phenomena in gen¬ 
eral, offer great promise and should be pursued fur¬ 
ther. Considerable thought should be given to the 
selection of a suitable location, and it would appear 
desirable for some branch of the military to establish 
facilities at the location, which preferably should be 
close to a shore laboratory. 

144 Measurements of Explosion-Generated 

Surface Waves 

Personnel of UERL have conducted experiments 
involving charges of from 300 to 30,000 lb to deter¬ 
mine the efficiency of explosive generation of surface 
waves and the associated underwater pressure varia¬ 
tions. 37 (See Section 1.2.9.) In general, the pressure 
variations on the bottom in shallow water were deter¬ 
mined. These are simply related to the amplitude of 
the surface waves if the latter are assumed to be sinu¬ 
soidal. 134 The present variations fall off with depth 
in a manner dependent upon the wavelength. The 
most successful measuring instrument was the NOL 
Mark 1 hydrophone in which the displacement of a 
diaphragm was measured electromagnetically. To 
check upon the absolute values observed with this 
hydrophone, other devices were developed at UERL 
but not extensively used. A sylphon differential pres¬ 
sure meter suitably protected against shock-wave 
damage gave results in good agreement with the NOL 
hydrophone. The pressure on the sylphon was re¬ 
corded electrically through the output of a photoelec¬ 
tric cell, the illumination on which was determined 
by the sylphon distortion. Some photographic records 
of the surface waves were taken, but these were diffi¬ 
cult to interpret satisfactorily. 

14 5 Location of Underwater Explosions 

One of the practical problems which UERL was able 
to solve satisfactorily was that of testing the fuzes on 
various types of underwater weapons to see whether 
they functioned under actual service conditions at 
the depths for which they were set. This problem 


provides an excellent illustration of the principle that 
practical problems can best be solved by making use 
of knowledge of the fundamental physics and chem¬ 
istry of the problem rather than by relying on 
strictly empirical procedures. Thus observations have 
been made on the nature of the domes and plumes 
from underwater explosions at various depths (75 ft 
and less) and this procedure has been employed to 
estimate the depth at which various depth bombs and 
depth charges function. At the time these investiga¬ 
tions were made, the bubble oscillation phenomenon 
was not known in this country so that the conclusions 
were based on purely empirical observations. Knowl¬ 
edge of the bubble oscillation phenomenon and its 
motion under gravity permits one to predict that the 
empirical method based on the time of appearance of 
plumes will be quite inaccurate at the depths of most 
interest. 135 ' 138 Because of the rapid upward motion 
of the bubble during its contracting phase, the time in¬ 
terval between the beginning of the surface phenom¬ 
enon and the break-through of the plume is not a 
sensitive function of the depth as had been assumed 
previously. The use of this time interval to determine 
depth can, therefore, not be recommended. 

The knowledge gained from their studies of the 
physics of underwater explosions enabled the staff at 
UERL to devise a number of successful methods of 
solving this problem which turned out to be quite 
simple to apply. 

The Sound-Ranging Method 

The most obvious method is to set up a sound- 
ranging system, that is to say, a series of sound pick¬ 
ups connected to an oscillograph system, so that the 
time intervals between the arrival of the shock wave 
at the various pickups can be measured. If the time 
interval between the arrival of the shock wave from 
an underwater explosion at two known points and the 
shock velocity over this interval are accurately known, 
the location of the explosion is restricted to a surface 
defined by the observed time interval, this surface 
being a hyberboloid of revolution about the line join¬ 
ing the two points. Two independent time interval 
observations are required to locate the explosion on 
a curve which is the intersection of two such surfaces. 
Three independent time intervals (from four pickup 
stations) would be required to fix the location of the 
explosion as a known point in space. 

In the system developed at UERL, 57 the arrival of 
the shock wave at three tourmaline piezoelectric 
gauges on a vertical line gave two independent time 


tO-S T FIDEXTIAL J 





60 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


intervals, and the results fix the explosion source as 
somewhere on a horizontal circle at depth D and of 
radius R, with the center on the vertical line through 
the gauges. (This system does not determine the di¬ 
rection of the explosion relative to the gauge line.) 
Additional time intervals from the arrival of surface 
and bottom reflections at the gauges may be used to 
obtain alternative values of the depth and to apply 
approximate corrections for deviations of the gauge 
line from the vertical. The gauge line was connected 
by 1,200-ft cables to recording oscillographs aboard 
a vessel holding the gear against the tide. A bomb tar¬ 
get was towed 100 ft from the gauge line. 

Several series of tests were conducted in Vineyard 
Sound on various fuze types in two types of aircraft 
depth bombs. 57,139 " 141 The bombs were dropped from 
airplanes traveling at about 150 knots at an altitude 
of about 100 ft. The results indicated that previous 
fuze-testing procedures were not valid, and that many 
of the fuzes tested under these conditions fired at 
considerably greater depths than they were supposed 
to, as determined by static calibrations in a pressure 
chamber. This malfunctioning confirmed suspicions 
which originated from an analyses of operational per¬ 
formance of the fuze types involved. 

Methods Based ox Observations of 
Surface Phenomena 

In conjunction with tests at shallow depths, several 
methods of determining the depth of explosions shal¬ 
low enough to produce surface upheavels have been 
developed. Many of these methods are modifications 
of the dome analysis methods. 142 ' 144 This method is 
based on the shape of the dome and is, in principle, 
independent of the charge weight. The shape of the 
dome is treated as determined by the obliquity of the 
shock wave to the surface as a function of the hori¬ 
zontal radius from the center of the dome, and the 
depth may be readily determined by rather simple geo¬ 
metrical considerations. A determination of a distance 
scale for the photographs is required. 

Several other methods employed the known relation 
between shock wave peak pressure and the spray par¬ 
ticle velocity in the dome. 57,58,145 As applied, this 
method involved an empirical extrapolation to deter¬ 
mine the initial spray velocity, because photograph¬ 
ically observed velocities were often abnormally high 
for the first few tenths of a second. LTse was made of 
the piezoelectrically determined dependence of the 
peak pressure on the distance from the bomb used. 


Both time- and distance-scaled motion pictures are 
required for these methods, and the calculations are 
sometimes tedious. 

A very simple empirical method was devised at 
UERL following a study of the surface phenomena 
of a series of Mark 54 depth bombs (250 lb of torpex) 
detonated at various depths from 15 to 75 ft. The 
ratio h D /d D , of the dome height to the diameter of 
the dome base at the time of the first plume phe¬ 
nomenon was found to be related to the depth by the 
empirical equation 

/ h D \-°- 67 

Depth (Mark 54) = 19.4 (—J ft. 

This method required neither time nor distance 
scales, and is recommended for use in the future for 
routine tests of production lots of fuzes. A calibration 
should be made, however, by firing at known depths, 
a series of the weapon in which the fuzes are to be 
used. LTnskilled personnel can be taught easily the 
proper procedure for smoothing (or averaging out) 
irregularities in the dome contour so as to get repro¬ 
ducible measurements of the ratio h D /d D . 

Determination of the Depth of Deep Explosions 

For the location of deep explosions, 146 the sound- 
ranging procedure was successfully modified so that 
pressure pickups could be positioned as deep as 800 
ft. A V 2 -lb charge was fired at a known position with 
respect to the ranging system within 2 sec after the 
weapon being tested had been detonated. By this 
means any deviation of the gauges from a vertical 
straight line, due to slight currents in the water, 
could be detected and corrected for. In addition, an 
independent and much simpler method was used, 146 
namely the measurement of the period of the bubble 
oscillation, which is a simple function of the depth 
(see Section 1.2.6). This method gave results in ex¬ 
cellent agreement with the sound-ranging method and 
is much easier to apply experimentally since only a 
single pickup and oscillograph circuit are required, 
and the pickup position is relatively immaterial. 

An extensive investigation of the British Squid 
projectile was carried out by the LTERL staff in 
Tongue of the Ocean in the Bahama Islands, utilizing 
a sound-ranging system and the bubble pulse method. 
As an example of the precision of these methods, 
Figure 30 shows the depth as a function of time for 
this weapon. It was possible to determine the location 
of an explosion 800 ft down with considerable pre¬ 
cision. 


’CONFIDENTIAf 





0 

100 

200 

300 

400 

500 

600 

700 

800 

900 


EXPERIMENTAL STUDY OF UNDERWATER EXPLOSION PHENOMENA 


61 


SINKING TIME IN SECONDS 

2 4 6 8 10 12 14 16 18 20 22 


ri- 

-,- 

T 


-1- 









vs\ 

\\3p 

vs\ 

v\\ 

vy 






A} 

\ 

\ 

\\\ 






% 

> 

i\ 






\ 

% 






\\\ 

\\\ 

\y 

\ 






% 

\\\ 

\ 

w 

\v\ 

\ 

\\ 


1 

1 

1 

1 

% 

o 

1 

\ 

\\ 

ySN 

\ 

\ 


Figure 30. Plot of sinking time-depth curve for Squid projectile. 


('O-Vl i D.KXT! \l4 































62 


UNDERWATER EXPLOSIVES AND EXPLOSIONS 


i.5 DESCRIPTION OF RESEARCH 
FACILITIES AT THE UNDERWATER 
EXPLOSIVES RESEARCH LABORATORY 

It seems worth while to give a brief description of 
the facilities available at UERL because the experi¬ 
ence gained in this undertaking might be useful to 
others planning to set up a laboratory for similar types 
of research. It should be stated that this laboratory 
was originally planned to be a very small group of 
perhaps half a dozen investigators but, as its problems 
multiplied, the project was expanded until it ultimate¬ 
ly had a total staff of between 80 and 100 persons. 
Naturally, many things would have been done differ¬ 
ently if the project had been planned for this size in 
its beginning stages. 

The requirement which determined the location of 
the laboratory was the availability of a well-equipped 
research laboratory with water of at least 20-ft depth 
in which explosions could be set off immediately ad¬ 
jacent to the laboratory. Although experiments with 
charges larger than a fraction of a pound could not 
be made at the location next to the building, neverthe¬ 
less, the possibility of carrying out small-scale experi¬ 
ments so conveniently was continuously utilized and 
was very important. It was, furthermore, necessary 
that there be deeper water at not too great a distance 
from the laboratory and that the surroundings not 
be built up to such an extent that the annoyance and 
damage caused by explosions would preclude work of 
this type. Questions of climate were considered but 
no location which seemed to be available met the 
ideal specifications in this regard. 

The location at Woods Hole involved working at 
the Woods Hole Oceanographic Institution [WHOI], 
which possesses a well-equipped research laboratory 
with office space, machine and carpenter shops, stor¬ 
age rooms, electric supplies of various types and, most 
important of all, a history of experience in carrying 
out experiments at sea. The town of Woods Hole pro¬ 
vided reasonably comfortable living conditions for the 
members of the staff and their families. 

Explosives were stored on a nearby island on which 
magazines were constructed. 147 The storage of explo¬ 
sives is one of the most difficult problems encountered 
in setting up a laboratory of this type. Experience 
showed that it was absolutely essential that supplies 
of explosives and storage of weapons for testing should 
be readily available and under the direct control of 
the laboratory. Whenever it was necessary to rely on 


other agencies for such explosives, delays were almost 
inevitable. 

Another essential feature of this laboratory was a 
casting or preparation house in which explosive 
charges were made up in the forms desired. This 
house was also located on the island and was of very 
simple construction. It contained melting kettles 
which were used for the preparation of cast charges 
of a great variety of shapes and sizes. This installa¬ 
tion also was under the complete control of the labo¬ 
ratory and was thus able to provide the needed charges 
without the delays which are so common when the 
jurisdiction over the supply is different from that of 
the laboratory. 

Explosives were fired underwater at a number of 
locations. Charges up to about half a pound were 
lowered to appropriate depths in the water adjacent 
to the institute dock. This was extremely convenient 
because short electric connections were possible to in¬ 
struments in the laboratory buildings. Work can be 
carried out very much more rapidly when the firing 
point is readily accessible to the main laboratory as it 
was in this case. For work with mechanical gauges re¬ 
quiring larger charges, say up to 25 lb, two especially 
designed floats were built which could be moored in 
the harbor where the water was about 60 or 70 ft 
deep. These floats consisted of two pontoons connected 
by a deck with a central well and carrying a quad- 
rupod mast for the cable blocks necessary for lowering 
the gear. In one model, the central well could be 
opened on one side by the removal of a portion of the 
deck. Charges were supported in the center of large 
steel rings to which were mounted the gauges. The 
ring could then be lowered and, if necessary for 
larger charges, floated from an oil drum out through 
the deck opening to a convenient distance from the 
moored raft. 

A small pond was also prepared on the island for 
work with electric gauges on charges up to 5 lb. 
This had many advantages. An overhead cable was 
strung; so that it was very convenient to launch the 
charges and equipment into the water. Furthermore, 
there were no waves or tide to contend with and a 
fixed installation could be set up on dry land. Experi¬ 
ence showed that work could be done several times 
faster when land based than when based on vessels. 
However, for charges of the size of service weapons, 
it was necessary to work from shipboard and for this 
purpose the schooner Beliance was fitted out as de¬ 
scribed in the Section 1.2.10. This proved to be a 


WFIDENTI 







DESCRIPTION OF RESEARCH FACILITIES 


63 


very successful arrangement but it was seldom pos¬ 
sible to fire more than two large charges a day where¬ 
as dozens of the small ones could be shot in the same 
time from the land based location. 

There were also available numerous beaches and 
locations of varying depth where special experiments 
such as on underwater cratering, effect of shallow 
shots, etc., could be carried out. This availability of 
varied types of water conditions was most helpful. 

One of the important features of the organization 
of this laboratory was the fact that those responsible 
for the scientific and technical direction of the project 
had complete authority and control over the various 
services such as explosive supplies, preparation of 
charges, operation of the vessels, etc. This placed a 
considerable burden of a nonscientific character on 
the technical people but it was felt, and experience 
demonstrated that this was correct, that only in this 
way could complete coordination and rapid progress 
of the work be made possible. Experience at other 
laboratories where divided authority existed has dem¬ 


onstrated that such an organization is not a good 
one for scientific research. It is, of course, necessary 
that decisions shell as, for example, the question of 
whether the weather is suitable for the safe operation 
of a vessel be left to the commanding officer of the 
vessel. However, if the commanding officer is respon¬ 
sible to the scientific director of the laboratory and 
not to some independent agency, he is more likely to 
make his decisions with the interest of the experi¬ 
mental project uppermost. It is also especially im¬ 
portant that these Service groups feel that they are 
part of the scientific organization and not merely 
being assigned to a certain branch of work for a tem¬ 
porary period. The difference between successful and 
unsuccessful scientific work depends on small differ¬ 
ences in the way in which numerous, not obviously 
important, precautions are followed through. The 
building up of the proper morale and spirit among the 
nontechnical employees is of the utmost importance 
in ensuring that the experiments are carried out in 
the way that is necessary to useful results. 


Confidential] 





Chapter 2 

EXPLOSIONS AND EXPLOSIVES IN AIR 


2.1 


2 . 1.1 


INTRODUCTION 


Purposes of Investigation 

E xplosives were employed in enormous quantities 
in weapons of many types throughout World War 
II. These weapons were used to cause injury to the 
enemy in specific ways. Some weapons, such as demoli¬ 
tion bombs, depth bombs and charges, explosive-filled 
shells, etc., were devised and used for the attack of 
structures such as factories, dwellings, fortifications, 
ships, and so on; other weapons, such as fragmentation 
bombs and shells, were intended to incapacitate 
personnel; demolition charges, including “hollow” 
charges, were employed in contact with obstacles, 
such as bridges, buildings, fortifications, etc., in order 
to breach the obstacle or to impair the usefulness of 
the structures to the enemy; and certain specialized 
devices depending on high explosives in the form of 
long, narrow charges were used for the passage of 
mine fields. For all of these weapons, even in the 
beginning of World War II, there was a choice among 
a number of high explosives as fillings, and as World 
War II progressed a large variety of new explosives 
was developed. 21 

The choice of a high explosive to be used in a par¬ 
ticular weapon was based on evaluation of a number 
of factors, among which a few were: 

1. The use to which the weapon was to be put. 

2. The requirement for sensitivity and stability 
of the high-explosive filling. (The stability and sensi¬ 
tivity of high explosives were investigated by Division 
8, NDRC.) 

3. The quantity of explosive required for the an¬ 
ticipated volume of production of the weapon. 

4. The best or most powerful explosive for the 
purpose. 

In order to select an explosive, then, it was neces¬ 
sary to evaluate, among other things, the power of the 
available explosives relative to each other, using as 
criteria those characteristics of performance most 
likely to be important in the contemplated use. 

In the case of weapons such as demolition bombs 
which produce damage by virtue of the air blast from 

a Pertinent to War Department Projects OD-Ol, OD-03, 
OD-79, OD-145, and to Navy Department Projects NO-11, 
NO-12, NO-144, NO-208, NO-224, and NO-283. 


their explosion, the evaluation of various explosives 
relative to each other was accomplished by comparing 
the air-blast intensities from corresponding quantities 
of the explosives in question. The order of merit of 
explosives for this purpose was then taken as the 
order of their air-blast intensities. 

As new explosives were developed, their perform¬ 
ance in air blast was measured, and the body of 
knowledge so obtained gave a basis for suggesting still 
other explosives for trial. Thus, a second valuable 
product of the comparisons of explosives was the 
steady improvement in the power of available military 
explosives, until, by the end of World War II, the 
performance of a bomb filled with one of the best 
explosives was estimated to be about twice that of a 
similar bomb filled with amatol 50/50, the usual 
filling for demolition bombs at the outbreak of this 
war. 

Studies of the behavior of shock waves, develop¬ 
ment of theories regarding them, and observation of 
the effects of weapons on targets made possible the 
prediction of the extent of damage to be expected from 
bombs of various fillings, and provided a basis for 
selection of bombs for tactical use in the way cal¬ 
culated to give maximum effect. Moreover, funda¬ 
mental knowledge of the physical laws governing the 
propagation and reflection of shock waves made pos¬ 
sible the development of a new and more effective way 
to use bombs of a given type: it was found that a 
bomb that bursts at the optimum height above the 
ground produces a blast wave of greater effectiveness 
than that from a bomb bursting on impact. This in¬ 
crease is estimated to correspond approximately to 
a doubling of the area of damage to be expected. 1 

Thus, a large bomb filled with a good explosive, 
fuzed so as to burst at the proper height, is estimated 
to be about four times as effective as the older types, 
fuzed instantaneouslv. 

J 

An important application of knowledge of the shock 
waves produced by explosions is in the evaluation of 
target vulnerability to various types of attack. By 
empirical or other means, the susceptibility of various 
targets to damage by blast has been estimated, and 
the blast intensities from various weapons determined. 
These data are useful in the design of structures to 
resist air attack. Similar use can be made of this in- 


64 







THE PHENOMENA OF EXPLOSIONS IN AIR 


65 


formation in specifying factors in the safe handling, 
transportation, and storage of high explosives. 

Throughout these investigations an important aim 
has been to broaden the fundamental knowledge con¬ 
cerning shock waves and explosives, for it is only 
on the basis of a good body of fundamental in¬ 
formation that the development of new weapons can 
be successful. 

212 History 

Prior to the beginning of World War II, it was the 
usual practice to assess explosives for use as fillings 
for aerial bombs by two general types of measure¬ 
ments : 

1. Tests were performed, such as the Trauzl lead 
block test, which assigned relative merits based on 
some property or properties of the explosive itself, or, 

2. A bomb containing the explosive was detonated 
in an enclosure surrounded by panels of wood, steel, 
etc., in order to determine the number and penetrat¬ 
ing power of fragments. 

Data obtained from the Trauzl block test, plate- 
denting tests, and measurement of detonation veloc¬ 
ities are associated with the brisance of the explosive. 
Although they provided information that is valuable 
for many purposes, the results are not directly per¬ 
tinent to the blast damage effectiveness of explosives 
since the more brisant of two explosives is not neces¬ 
sarily the one that produces the greater blast intensity. 
Similarly, fragmentation in a very large blast bomb, 
in which the explosive to case-weight ratio is as great 
as possible, is usually not pertinent to the use to which 
such bombs are put. 

Aside from the question of which explosive filling 
has the greatest blast effectiveness, there are several 
other ways in which air-blast measurements are es- 
sential and for which no other type of measurement 
suffices. For example, it is desirable to have a quan¬ 
titative measure of the parameters that describe the 
shock wave in order that the intensity thus measured 
can be related by some means to the damage which 
the wave accomplishes. Without such information, 
the only way in which the effectiveness of a weapon 
can be estimated is by observing its effect on targets 
themselves. The effects of charge shape, thickness and 
composition of the case, etc., on the blast effectiveness 
of a weapon are best determined by measuring blast 
intensities. It is also important that the interactions 
of shock waves with their surroundings by reflection, 
absorption, etc., be quantitatively determined by 
means of blast measurements. 


The development of blast-measuring techniques and 
their application to the evaluation of weapons was 
begun in England at the Road Research Laboratory 
[RRL] in 1938, and later, at the Armament Research 
Department [ARD]. In the United States, similar 
developments were undertaken in 19-11 and 1942 by 
the Princeton University Station, Division 2, NDRC, 
the Ballistic Research Laboratory [BRL], Aberdeen 
Proving Ground, the David Taylor Model Basin 
[DTMB], and Harvard University [HU], Divisions 
8 and 2, NDRC. Blast measurements using 4,000-lb 
bombs were first performed in the United States at 
Aberdeen Proving Ground in December 1942, with 
BRL, DTMB, and HU participating. In 1943, the 
development and operation of blast-measurement ap¬ 
paratus was undertaken by the Stanolind Oil and Gas 
Company [SOG]. At the same time, the HU group 
was transferred to the Underwater Explosives Re¬ 
search Laboratory [UERL] at Woods Hole Oceano¬ 
graphic Institution [WHOI]. 

The early applications of blast measurements were 
concerned with evaluation of the performance of new 
bombs, determination of the effects of booster design 
on performance, etc. As new explosive compositions 
became available, extensive comparative tests on 
bombs and charges of all sizes were carried out. By 
the end of 1943, the relative merits of several of the 
most important explosives had been determined, and, 
as a consequence, the older explosives (usually of the 
amatol type) had been replaced as service fillings by 
the newer, more powerful explosives. In Great Britain, 
particularly, the fullest advantage was taken of every 
means by which the blast effectiveness of bombs could 
be enhanced. 

In addition to studies of the relative effectiveness 
of explosives, blast measurements were made in order 
to determine the effect of case-weight on blast, the 
properties of shock waves obliquely reflected from 
surfaces, the blast intensities from line charges, the 
blast from explosions in igloo-type storage magazines, 
and a number of other properties of explosions. 

2.2 THE PHENOMENA OF EXPLOSIONS 

IN AIR 

221 The Detonation of High Explosives 

High explosives release their energy by a process 
called detonation, and low explosives, or propellants, 
by a process of rapid burning. The time required for 
the detonation of a quantity of high explosive is 


U’.VJ- ibK.VJ I AI, 







66 


EXPLOSIONS AND EXPLOSIVES IN AIR 


much less than that for the burning of a like amount 
of propellant. With high explosives, the rate of deto¬ 
nation is not markedly affected by the particle size; 
with propellants, the grain size is all-important. The 
shattering effect of a high-explosive detonation is 
great; that of a propellant explosion much less. These 
distinctions are not completely clear-cut, however. 

Several low explosives can be made to detonate; 
even black powder, under great pressure, may deto¬ 
nate under the proper conditions. The military uses 
to which high explosives are put depend upon their 
great shattering power (brisance) and their high 
rate of detonation. 

Some high explosives, such as mercury fulminate, 
lead azide, etc., are very sensitive to heat, shock, etc., 
and can be easily detonated by a spark or other local 
application of heat. These explosives are used to 
initiate less sensitive explosives and are called primers. 
Other explosives that are less sensitive to shock and 
heat than primers but in which detonation can be 
initiated by primers, are used as boosters, i.e., inter¬ 
mediates between the primer and the main body of 
explosive, capable of being initiated by the former 
and of initiating the latter. The most important of 
the explosives used as boosters is tetryl. The main ex¬ 
plosive filling is very insensitive to shock, heat, fric¬ 
tion, etc., and must be detonated with the aid of a 
booster. The quantities of these three types of explo¬ 
sive in a given weapon differ greatly. (1) A very 
small quantity of primer, usually less than 1 gram, 
is used, (2) the booster weight is ordinarily of the 
order of a fraction of a pound to a few pounds, and 
(3) the bulk of the explosive content of a weapon is 
the insensitive main filling, which may constitute over 
1)9 per cent of the total amount of explosive. 

The explosion of the booster gives rise to a com¬ 
pression wave in the main explosive filling. If no 
further action were to take place, i.e., if detonation 
in the main filling did not occur, this compression 
would be propagated as a wave, at approximately the 
velocity of sound, through the explosive. However, if 
the compression is sufficient, chemical reaction of the 
explosive will take place as a consequence of the ele¬ 
vated pressure and temperature in the compressional 
wave. This chemical reaction is exceedingly rapid, 
and the chemical products of the reaction have a very 
high pressure and temperature. This zone in which 
the chemical reaction takes place, called the detona¬ 
tion wave, is propagated through the explosive at a 
velocity considerably in excess of the velocity of sound 


in the explosive and is preceded by a compression wave 
which it supports. 

The velocity of propagation of the detonation wave, 
called the detonation velocity, depends on the chem¬ 
ical and physical properties of the explosive and, to 
some extent, on the dimensions of the mass of explo¬ 
sive and the degree of confinement. Most military 
high explosives have detonation velocities of the order 
of 5,000 to 8,000 m per sec, i.e., 16,000 to 26.000 fps. 

Theories have been developed 2 ’ 3 that make it pos¬ 
sible to compute the detonation velocity, the pressure 
and temperature in the detonation wave, and the 
chemical processes that occur. These theoretical results 
have been confirmed in large part by direct experi¬ 
ment. (See Summary Technical Report of Division 8.) 

When the detonation wave reaches the interface 
between the explosive and the air that surrounds it 
(the charge unconfined) the products of the detona¬ 
tion, largely gases, expand with high velocity, pres¬ 
sure, and temperature. The boundary between the air 
and the hot compressed gases is sharply defined. The 
outer layer of the burnt gases is theoretically at a 
very high pressure (initially of the order of 10,000 
psi). Behind this layer the pressure and temperature 
at a short time interval later decrease rapidly to 
lower values toward the interior of the charge. The 
rate of expansion of the luminous zone, presumably 
the hot burnt gases, continually decreases. Eventually 
another discontinuity emerges from the luminous zone 
and thereafter leaves it behind. This is the shock 
wave, a sharp discontinuous rise in pressure propagat¬ 
ing through the air surrounding the explosion prod¬ 
ucts. Throughout the expansion of the hot gases, the 
chemical composition of the reaction products changes 
as their pressure and temperature change. 

If the charge is confined by a metal case, such as 
the steel case of a bomb, the case is expanded by the 
pressure of the hot gases. At first, the metal flows 
plastically, until the volume of the case has been in¬ 
creased considerably (about twofold for steel cases), 
and then rupture takes place. The resulting fragments 
of the case are propelled at high velocity, and since 
they are not at first retarded so much as is the shock 
front they precede the shock wave over a great dis¬ 
tance from the charge. The acceleration of the frag¬ 
ments requires energy, of course, and a considerable 
fraction of the detonation energy of the explosive may 
be carried away by the fragments. As a result, the 
energy, and hence the pressure, etc., of the shock 
wave from a confined charge are considerably less 







THE PHENOMENA OF EXPLOSIONS IN AIR 


67 


than from an uncased explosive charge. Extensive in¬ 
vestigations of fragmentation have been carried out 
and are described elsewhere. 4 10 

At the boundary between the burning gases and the 
surrounding air, oxygen comes in contact with the 
hot reaction products. Since most explosives do not 
contain sufficient oxygen to burn the carbon and 
hydrogen (and aluminum) completely, the product 
gases are capable of further (slow) oxidation. These 
reactions may take place at the surface between hot 
gases and air, or they may occur within the flame 
region when mixing with the air takes place. In any 
event, these processes are slow compared with the very 
rapid detonation process. Additional energy is released 
by this means, and the shock-wave intensity is en¬ 
hanced. The processes described are called afterburn¬ 
ing. Of the total energy available for complete com¬ 
bustion of the explosive, only about one-third is pro¬ 
duced by the detonation. Therefore, if afterburning 
were complete, the energy from that source would be 
about twice that from detonation. 

2.2.2 The Propagation of the Shock 

Wave in Air 

The rapid expansion of the mass of hot gases result¬ 
ing from detonation of an explosive charge gives rise 
to a wave of compression called a shock wave which 
is propagated through the air. The front of the shock 
wave can be considered infinitely steep, for all prac¬ 
tical purposes. That is, the time required for com¬ 
pression of the undisturbed air ahead of the wave to 
the full pressure just behind the wave is practically 
zero. 

If the explosive source is spherical, the resulting 
shock wave will be spherical, and, since its surface is 
continually increasing, the energy per unit area con¬ 
tinually decreases. As a result, as the shock wave 
travels outward from the charge, the pressure in the 
front of the wave, called the peak pressure, steadily 
decreases. At great distances from the charge, the 
peak pressure is infinitesimal, and the wave, therefore, 
may be treated as a sound wave. 

Behind the shock-wave front, the pressure in the 
wave decreases from its initial peak value. Near to 
the charge, the pressure in the tail of the wave is 
greater than that of the atmosphere. However, as the 
wave propagates outward from the charge, a rarefac¬ 
tion wave is formed which follows the shock wave. 
At some distance from the charge, the pressure be¬ 
hind the shock-wave front falls to a value below that 


of the atmosphere, and then rises again to a steady 
value equal to that of the atmosphere. The part of the 
shock wave in which the pressure is greater than that 
of the atmosphere is called the positive phase, and, 
immediately following it, the part in which the pres¬ 
sure is less than that of the atmosphere is called the 
negative or suction phase. 

The velocity at which the shock wave is propagated 
is uniquely determined by the pressure in the shock- 
wave front and the pressure, temperature, and com¬ 
position of the undisturbed medium. The greater the 
excess of peak pressure over that of the atmosphere, 
the greater the shock velocity. Since the pressure at 
the shock front is greater than that at any point be¬ 
hind it, the wave tends to lengthen as it travels away 
from the charge, i.e., the distance between the shock 
front and the part at which the pressure in the wave 
has decreased to atmospheric continually increases. 
For a discussion of the theory of shock waves see the 
bibliography. 11 

A gauge that is capable of indicating the pressure 
instantaneously applied and that is fixed with respect 
to the charge will record the pressure in the wave as 
a function of time. The resulting pressure-time curve 
bears a close resemblance to the pressure-distance 
curve described above: there is an initial abrupt rise 
in pressure followed by a relatively slow decrease in 
pressure to a value below that of the atmosphere. The 
time elapsing between the arrival of the shock front 
and the arrival of the part in which the pressure is 
exactly atmospheric is called the positive duration, 
and this, like the length of the wave, increases as the 
wave travels away from the charge. A quantity of 
interest in the application of blast measurements is 
the positive impulse which is the average pressure 
during the positive phase, multiplied by the positive 
duration. 

Associated with the propagation of the shock front 
is a forward motion of the matter behind the shock 
front and the conditions that determine the shock 
velocity also determine the particle velocity. In gases, 
such as air, the particle velocity for high-shock pres¬ 
sures is very high. For example, at about 3 atmos¬ 
pheres excess pressure in the shock front, the particle 
velocity immediately behind it is about 700 mph. 

The temperature behind the shock front is also 
greater than that ahead of it because of the compres¬ 
sion of the medium. Since this compression is irre¬ 
versible, the temperature of the air through which the 
shock wave has passed and which has returned to 


CO V'Fi ! )K\T! A f j I 






68 


EXPLOSIONS AND EXPLOSIVES IN AIR 


atmospheric pressure is somewhat greater than that 
of the undisturbed air prior to the arrival of the 
shock wave. This irreversible heating of the air is 
less, the smaller the excess pressure in the shock 
wave. 

At a very great distance from the charge, the wave 
becomes acoustic, i.e., the pressure rise, temperature 
rise, and particle velocity are all infinitesimal, and the 
velocity of the wave is that of sound. 

2 2 3 The Interaction of Shock Waves 
with Their Environment 

Very weak shock waves, i.e., those of nearly acoustic 
strength, are reflected from plane surfaces in such a 
way that a geometrical construction of the wave sys¬ 
tem can be made in a very simple way. Consider a 
point source of the shock C (Figure 1) and, some dis- 



Figure 1 . Reflection of weak shock waves. 

tance from it, a plane reflecting surface S. The inci¬ 
dent wave I, striking the surface, will be reflected 
from it in such a way that the reflected wave R may 
be considered to arise from a second image source C' 
on the opposite side of the reflecting surface, perpen¬ 


dicularly below the true source and equally distant 
from the surface. 

Figure 1 shows two successive stages of this reflec¬ 
tion process. In the first, I 19 the incident wave is just 
tangent to the surface. The excess pressure over that 



of the atmosphere at the reflecting surface is just 
double (for very weak shock waves) that of the inci¬ 
dent wave where it is not in contact with the surface. 
At a later stage, the incident wave is represented at I 2 
and the reflected wave at R 2 imagined to arise from 
the image source C'. Again the pressure at the line 
of contact of I 2 , R 2 , and the surface S is just double 
that of I 2 . The angles at which the shocks I 2 , R 2 meet 
the surface S are equal. 

When the pressure in the shock wave is appreciably 
above that of the atmosphere, the phenomena are dif¬ 
ferent. One reason for this is that the pressure, den¬ 
sity, and velocity of the air into which the reflected 
shock advances are not those of the undisturbed atmos¬ 
phere. In Figure 2 are represented three successive 
stages in the reflection of strong shocks. In the termi¬ 
nology used above, the incident wave I 1 is first shown 
just as it touches the reflecting surface S. The excess 
pressure above that of the atmosphere at this point 
is more than twice that of I x elsewhere, and the mag¬ 
nitude of the increase of pressure over that of I t is 
determined by the strength of I 1 . For example, if the 
peak (excess) pressure of is 100 psi, the reflected 
shock pressure is about 500 psi, a fivefold increase of 
pressure. (See data sheet 3A3 of Chapter 19.) 

As the incident wave expands to some greater size 
/ 2 , the reflected wave R 2 also expands but the re¬ 
flected wave is not spherical and cannot be constructed 
by the device used in Figure 1. The angles at which 
I 2 and R 2 meet the surface S are not equal, in 


. !>\ i I 1'K \ l'l.\f| 


















EXPERIMENTAL METHODS AND APPARATUS 


69 


general, and the angle of the reflected shock R 2 de¬ 
pends upon the strength and angle of incidence of 
the incident shock. 

At some distance from the charge C, determined 
by the distance of C from S and by the strength 
of the incident shock, a new phenomenon occurs. 
The intersection of R and I no longer lies on S but 
lies above it and follows some path, /. A new shock, 
M, the Mach stem, connects the intersection of R and 
1 to the surface. The intersection of R } I, and M is 
called the triple point. As the shock system expands 
further, the Mach stem grows rapidly, tending to 
swallow up the two-shock system above it. If C is 
very close to the surface, but not on it, the Mach 
stem is formed almost directly under C, and, in a 
short time, has grown so that most of the shock sys¬ 
tem is a Mach stem, and only in a small region 
directly over the charge are R and I distinct. If the 
charge C is on the surface 8, no separate reflection 
R is formed, and it can be considered that the entire 
shock wave is a Mach wave. 

A very practical property of the reflection of shocks 
is that the pressure (and positive impulse) in the 
neighborhood of the triple point and in the Mach 
stem are considerably greater than those in / 3 or in 
the shock emitted when C is in contact with S. That 
is, if C is a bomb bursting above the ground repre¬ 
sented by S, the intensity of the blast in the region 
M and just above it is greater, at a given horizontal 
distance from the bomb, than is the case if the bomb 
is burst in contact with the ground. 

When a shock wave strikes a nonrigid obstacle, 
such as a building, the wave is reflected by the sur¬ 
faces of the building in the various ways described 
above. The reflection from a nonrigid surface will not, 
however, conform quantitatively to that from a rigid 
surface such as that discussed above. At the instant 
the wave strikes the wall, the wall is accelerated and 
continues to accelerate as long as there is an excess 
of pressure on its outer surface. At first, the deforma¬ 
tion of the wall is elastic, so that for insufficient excess 
pressure or insufficient positive duration there may 
be no permanent displacement of the wall. If the 
blast intensity is sufficient, the wall eventually de¬ 
forms inelastically and suffers permanent displace¬ 
ment. If, for the wall in question, the displacement 
is greater than some critical amount, the wall will 
collapse. 

A simplified picture of the processes of damage 
consists of a wall of indefinite extent which has a 


certain natural period of vibration. If a shock wave 
of very long duration strikes it, the wall can be con¬ 
sidered to be subjected suddenly to a blast of constant 
pressure equal to the pressure in the shock wave en¬ 
hanced by reflection. For sufficiently small pressures, 
the wall will deform elastically (the amount of the 
displacement being about twice that from a static 
pressure equal to the pressure in the reflected blast) 
and will not rupture. Some pressure must exist, how¬ 
ever, such that the wall will collapse. For shock waves 
of finite duration, the wall may not collapse even 
though the pressure is equal to the critical pressure. 
Instead, the wall will acquire momentum from the 
shock wave and will vibrate, without reaching the 
amplitude corresponding to collapse. If the duration 
of the wave is very short compared with the time 
required for collapse, the momentum imparted to the 
wall must be sufficient to deform it beyond the critical 
limit. On the basis of reasoning such as this, the peak 
pressure is usually considered to be the determining 
factor in the damage produced in the blast from very 
large bombs, such as atomic bombs. For small bombs 
it is generally assumed that the positive impulse is 
the important quantity, since the duration of the 
blast is quite short. Unfortunately, neither operational 
experience nor experiment is adequate to test these 
criteria properly. A reference for a more detailed an¬ 
alysis of this problem is given in the bibliography 12 
and the subject of damage is treated in Chapter 1G 
of this volume. 

2.3 EXPERIMENTAL METHODS AND 

APPARATUS 

231 Electrical Methods for Measuring 
Pressure versus Time 

The Use of Piezoelectric Gauges 

For the measurement of air-blast pressures the 
most common method employs piezoelectric gauges. 
Of all piezoelectrically active crystalline substances, 
those that have been used in gauges are tourmaline, 
quartz, Rochelle salt, and ammonium dihydrogen 
phosphate [ADP]. 

A piezoelectric substance is one that produces on 
its surfaces an electric charge when the crystal is 
strained. In gauges, slabs of the crystal, cut in such 
a way as to produce the maximum charge, are pro¬ 
vided with metallic electrodes. To these electrodes are 
attached the conductors of an electric cable which con¬ 
nects the gauge with the recording apparatus. The 


n.\ i ! i- ; \ t■ \i.| 





70 


EXPLOSIONS AND EXPLOSIVES IN AIR 


fundamental advantageous property of piezoelectric 
gauges is their quick action that responds to transient 
pressure changes of very short duration. 

Tourmaline is fairly abundant and can be obtained 
in rather large crystals. It differs from the others 
listed in that it produces a net electric charge when it 
is subjected to uniform hydrostatic pressure. Its sensi¬ 
tivity, in terms of the electric charge produced for 
unit pressures, is about the same as that of quartz. 
Quartz, like tourmaline, is fairly abundant and in¬ 
soluble in water. Unlike tourmaline, however, if 
quartz is subjected to a uniform hydrostatic pressure, 
no net electric charge is produced on its surfaces. 
When quartz, Rochelle salt, or ADP, is used in a 
gauge, it is necessary to seal the edges of the crystal 
slabs from the blast pressure by a rigid housing, 
which is usually made of metal. Pressure, then, is 
applied only unidirectionally to the crystal slabs. 
Rochelle salt differs from quartz in its sensitivity; 
gauges made of Rochelle salt are about a hundred¬ 
fold more sensitive than are those of the same size 
made of quartz. The disadvantages in the use of 
Rochelle salt are that it is soluble in water, and that 
there is a rather high temperature coefficient of pres¬ 
sure sensitivity. ADP is intermediate in temperature 
sensitivity and pressure sensitivity between quartz and 
Rochelle salt. Although all four crystalline materials 
have been successfully used in piezoelectric gauges, 
the tendency has been to turn finally either to tourma¬ 
line or to quartz. 

One property that is possessed by all piezoelectric 
substances is pyroelectric activity. That is, these sub¬ 
stances produce an electric charge as a result of a 
change in their temperature. Tourmaline produces a 
net charge when it is heated uniformly as well as 
nonuniformly. Quartz, Rochelle salt, and ADP, how¬ 
ever, do not produce a net charge as a result of uni¬ 
form heating. The charge produced by a temperature 
change of 1 C in tourmaline is about equal (and oppo¬ 
site in sign) to that produced by a pressure of 250 
psi. For this reason, the piezoelectric crystal slabs 
in a gauge must be carefully protected by adequate 
thermal insulation from the effects of transient tem¬ 
perature changes. 

A tourmaline gauge consists of a pile of disks of 
tourmaline, sawed from the crystal, and each provided 
with closely adhering metal electrodes on the sawed 
faces. The disks are so arranged in the pile that the 
charges produced on contiguous electrodes are of the 
same sign. Lead wires are soldered to the electrodes 
and attached to the electric cable. An electric shield 


surrounds the pile and is connected to the shield of 
the cable. Finally, the whole assembly is coated with 
a material that is a good thermal insulator. 

The quartz gauge, which has been used very success¬ 
fully in England by RRL and ARD, consists of a pile 
of quartz disks, provided with a thin metal cap or 
piston and sometimes with a plate of fused quartz to 
provide thermal insulation. The pile is mounted in a 
massive steel body, and a seal of viscous oil around 
the piston (at RRL) or a sheet of tin foil across the 
face of the gauge (at ARD) prevents leakage of air 
into the body of the gauge. References for the design, 
calibration, and use of tourmaline gauges 13 ' 21 and 
quartz gauges 20 ' 22 are given in the bibliography. 

The gauges are calibrated by applying known pres¬ 
sures and observing the magnitude of the electric 
charge produced. Over very wide ranges of tempera¬ 
ture and pressure, the pressure sensitivities of tour¬ 
maline and quartz gauges are constant. In measuring 
blast pressures, however, if the gauge projects into 
the flow of air behind the shock front, the wave is dis¬ 
turbed, and the gauge records the pressures of this 
disturbed wave which differ from those in the undis¬ 
turbed wave. This difficulty is common to all gauges 
(not only piezoelectric ones) used in this way. It can 
be overcome by mounting the gauges flush with the 
surface of a rigid baffle, or of the ground; by this 
means, the gauge does not disturb the air flow and 
does record the true pressures in the wave. 

In addition to the gauges themselves, coaxial elec¬ 
tric cables, amplifiers, calibration circuits, and means 
of recording are necessarv. The coaxial cables must 
be free from spurious electric signals when struck by 
shock waves and from distortions of the gauge signal 
arising from dielectric absorption. 24,25 Since the gauge 
generates an electric charge, the voltage of the output 
signal from the amplifier depends upon the electric 
capacity of the system and hence upon the length of 
the coaxial cable. 

Amplifiers of adequate gain, low- and high-fre¬ 
quency response, stability, and linearity must be used. 
Since the electric signals usually obtained in this 
work are of the order of a few millivolts, the ampli¬ 
fication required is considerable. 

Calibration of the overall electric charge sensitivity 
of the cables, amplifiers, and recording apparatus, and 
of the time base must be made. These involve record¬ 
ing the output of the apparatus when an electric cali¬ 
brating signal of known voltage (corresponding to a 
known electric charge) and another of known fre¬ 
quency are applied to the input of the apparatus. 


« OM'inKXT! Vli 







EXPERIMENTAL METHODS AND APPARATUS 


71 


Recording of the amplifier output voltage versus 
time is usually done by use of cathode-ray tubes 
and photographic recording of the traces on their 
screens. The very high range of frequencies which the 
cathode-ray tube can reproduce faithfully makes it 
particularly suitable for this work. It does, however, 
have the disadvantage of being rather insensitive, re¬ 
quiring considerable amplification of the low-level 
gauge signals. Time resolution is usually provided by 
moving the film in a direction perpendicular to the 
deflection of the trace on the cathode-ray tube. 
Although moving film is preferred, stationary film 
has been used by deflecting the cathode ray in the 
proper direction at a constant rate by means of an 
electronic single-sweep generator. 

The oscillogram thus obtained can be interpreted 
as a pressure-time curve, by means of the calibrations 
of gauge-charge sensitivity and time. Figure 3 repre¬ 
sents a typical oscillogram of a pressure-time curve. 

In Figure 3, the atmospheric pressure prior to the 
arrival of the shock wave at the gauge is represented 
bv the horizontal line P Q . At the time t — 0, the shock 


p 



Figure 3. Typical oscillogram of pressure-time curve. 

wave arrives at the gauge and the pressure is almost 
instantaneously increased to P, the peak pressure. 
Thereafter, the pressure decays relatively slowly, until 
at t c , the “crossing time,” the pressure is again atmos¬ 
pheric. The time t c is the positive duration of the 
wave. After t c , the pressure decreases and a region of 
suction (S) follows the positive pressure phase. The 
pressure then again returns to atmospheric. The cross- 
hatched area bounded by t — 0, P, and t c , is propor¬ 
tional to the positive impulse of the shock wave. 

The advantages of the piezoelectric technique are 
the wide range of pressures at which the gauge may 
be used, its high-frequency response, its linearity with 
pressure, and the comparatively simple auxiliary ap¬ 
paratus. The disadvantages of the method are the 
relatively low sensitivity, the high time constant re¬ 
quired of gauge, cable, and amplifier input circuit 
(necessitated by the fact that the gauge is a charge- 
generator), and the pyroelectric sensitivity of the 
gauge. 

References to descriptions of apparatus for use 


with piezoelectric gauges are contained in the biblio- 

14~16,20~22,24-30 

The Condenser-Microphone Technique 

The condenser-microphone gauge has been recently 
developed for use in measuring air-blast pressures. A 
condenser-microphone consists of two parallel metal 
plates mounted so as to be insulated from each other, 
and separated by a dielectric (air, mica, etc.). The 
two plates, which are the plates of a condenser, are 
connected to the associated electronic apparatus by 
means of an electric cable. Under the application of 
pressure, the dielectric between the condenser plates 
is reduced and the capacity of the condenser therefore 
increases. 

In one type of apparatus, the gauge condenser is 
connected as part of a tuned circuit in a transmitter. 
The change in the resonant frequency of this circuit 
is linearly dependent on the pressure applied to the 
gauge over the range of pressures for which the gauge 
was designed. The output signal (frequency-modu¬ 
lated) of the transmitter is applied to the input of a 
receiver either via an electric cable or by radio trans¬ 
mission. The frequency-modulated signal is amplified, 
demodulated, and again amplified, and the output is 
applied to the recording apparatus. The gauge can 
also be used in amplitude-modulation devices. Either 
cathode-ray oscillographs or galvanometer oscillo¬ 
graphs can be used for recording, depending upon the 
frequency-response requirements. Apparatus of these 
types has been used by BRL, 31 General Motors Re¬ 
search Division, 32 the Research Department, Wool¬ 
wich, 33 Princeton University Station, 34 and the Ex¬ 
plosives Research Laboratory. 35 

A modification of this system, developed at BRL, 31 
is used to make a direct simple measurement of posi¬ 
tive impulse. The frequency-modulated signal from 
the transmitter is caused to beat against an oscillator 
in the receiver. The resulting beat-frequency signal 
is amplified and “sharpened” to produce pulses of a 
few fxsec duration. These pulses drive neon lights 
whose flashing is recorded on moving film. Since the 
frequency of the signal is proportional to the pressure 
applied to the gauge, the time integral of the pressure 
over the positive duration (i.e., the positive impulse) 
is proportional to the difference between the number 
of flashes and the number that would have occurred 
without a pressure pulse. Then the interpretation of 
the photographic record consists simply of counting 
dots. 

The advantages of the condenser-microphone tech- 


lOXFTDEXTIALj 











72 


EXPLOSIONS AND EXPLOSIVES IN AIR 


nique are: (1) the system has no inherent limitation 
on low-frequency response, i.e., it can respond to 
static pressures; (2) the gauge can be made relatively 
free from transient thermal effects; (3) the system 
has essentially no interference from cable signal, low- 
frequency pickup on cables, and microphonics, and 
does not require high impedance in the gauge circuit ; 
and (4) it is particularly well adapted to the use of 
transmission by radio, thus replacing electric cables. 
The disadvantages of the system are: (1) the pressure 
range over which a particular gauge will operate is 
relatively small, thus necessitating the selection of a 
gauge to suit each expected condition; (2) the gauge 
has a natural period of vibration which limits its high 
frequency response; and (3) for use at distances of 
the order of 1,000 ft between gauge and recording 
apparatus, electronic apparatus (transmitter, power 
supply, or batteries, etc.) must be located at the 
gauge, thus complicating the problem of servicing. 
The further development of this method offers prom¬ 
ise of a great improvement in the techniques of air- 
blast measurement. 

The Resistor Gauge Method 

A third device for measuring transient pressures 
depends on the change of electric resistance of an 
element under stress. In one form, the gauge consists 
of a resistance element that is hydrostatically com¬ 
pressed. In another, a resistance wire is formed in a 
spiral and cemented to the back of a diaphragm con¬ 
strained at its periphery. When pressure is applied, 
the diaphragm is deformed, the wire is stretched and 
the resistance of the wire changes. 

Associated with the gauge is a simple potentiometer 
circuit by means of which changes in resistance give 
rise to proportional changes in voltage. These voltage 
changes are amplified and recorded. The principal 
development of resistance-strain gauges of the dia¬ 
phragm type has been effected by the Navy Depart¬ 
ment at DTMB. 36,37 

The advantages of the resistance type of gauge are, 
(1) the gauge has no limitation on its low-frequency 
response, i.e., it is capable of measuring static pres¬ 
sure; (2) the gauge and its method of operation are 
relatively simple; and (3) the gauge circuit is low 
impedance. The disadvantages of the system are, (1) 
the gauge is usually quite insensitive, thus requiring 
a rather high gain amplifier; (2) the gauge is subject 
to hysteresis; (3) there is a characteristic oscillation 
of the diaphragm which limits its high-frequency re¬ 
sponse; and (4) the pressure range over which a 


given gauge will operate is relatively small, and a 
gauge must, therefore, be selected to conform to the 
requirements of each use. 

Other Electric Methods for Measuring 
Pressure as a Function of Time 

Gauges based on magnetic properties have been 
used in numerous applications and have been pro¬ 
posed for use in measuring air-blast pressures. Sev¬ 
eral possible types have been suggested: moving-coil 
or moving-magnet gauges, moving diaphragm gauges, 
and magnetostrictive gauges. Some of these types 
offer possibilities for gauges of high-output voltage 
or of great compactness. One advantage would be the 
low-impedance characteristics. 

2 . 3.2 Mechanical Gauges for Measuring 
Pressure, Impulse, etc. 

Gauges Based on the Spring-Piston Principle 

A gauge for measuring peak pressure has been de¬ 
signed that operates by recording the maximum ex¬ 
tension of a spring acted upon by a moving piston 
which is accelerated by the action of a pressure pulse. 
If the natural period of the piston-and-spring is short 
compared with the duration of a transient pressure 
pulse, the maximum extension of the spring is pro¬ 
portional to the peak pressure of the pulse. 

One gauge of this type which has been successfully 
used for measuring air-blast pressures is the Naval 
Ordnance Laboratory [NOL] ball crusher gauge. 38 ' 40 
This gauge consists of a massive block in which is 
fitted a sliding piston, a fixed anvil, and between 
them, a spherical copper ball. The plastic-flow char¬ 
acteristics of the ball give a very nearly linear re¬ 
sisting force. The maximum compression of this 
spring is measured by the permanent deformation of 
the ball. Although, in principle, the dimensions and 
mass of the piston and diameter of the ball can be 
chosen arbitrarily, in practice there is an upper limit 
to piston area per unit mass, and a lower limit to the 
size of ball. x4s a result, the gauge is best suited for 
measuring high peak pressures. The standard NOL 
gauge (as developed for underwater use) has been 
used successfully at air-blast pressures as low as 50 psi. 

Another type of gauge 41 based on the same prin¬ 
ciple is the LTERL spring-piston gauge. This consists 
of a moving piston, helical spring, and a simple means 
of recording the maximum stroke of the piston. This 
gauge can, in principle, be designed to measure blast 
pressures in any range where the positive duration is 
large, but the relatively delicate mechanism estab- 


COXI’IDF.NTTATi 





EXPERIMENTAL METHODS AND APPARATUS 


73 


lishes a practical upper limit to pressure estimated to 
be about 100 psi. 

For measurement of blast intensities from charges 
of moderate size with which the positive durations 
encountered are not extremely long, the spring-piston 
gauge is capable of precise measurement of positive 
impulse. For this purpose, the piston mass and spring 
strength are adjusted so that the natural period of the 
mass is about four times the positive duration of the 
blast. Under these conditions, the maximum compres¬ 
sion of the spring is a measure of the positive 
impulse. 

The Williams gauge 42 is a device that has been 
used for many years as an approximate peak-pressure 
indicator. It consists of a very light piston moving in 
a closely fitting cylinder and working against the air 
in the cylinder, which it compresses. The maximum 
compression is recorded by a simple device. The air in 
the cylinder behaves as a nonlinear spring. The chief 
difficulties with the gauge are that a very small fric¬ 
tion (such as that caused by dust) introduces large 
errors in the readings and that the range of pressures 
which can be read with a given gauge is quite small. 
Moreover, the theory of the gauge operation is not 
completely developed. 

The advantages of the ball-crusher gauge are, (1) 
simplicity of construction and operation, and (2) 
applicability to measurements of high pressure. The 
disadvantage is that the gauge is too insensitive to be 
used below about 50 psi. The advantages of the UERL 
spring-piston gauge are: (1) its applicability to the 
measurement of relatively low peak pressures; and (2) 
the high precision of results. The disadvantages are: 
(1) the gauge is relatively complicated, requiring 
fairly elaborate machine work; (2) it is only moder¬ 
ately rugged; and (3) very high blast pressures would 
be difficult to measure. The two types, ball crusher 
and spring-piston, complement each other in the 
ranges of pressure to which they can be best applied. 

Gauges Based on the Feee Piston Peinciple 

For the measurement of positive impulse, gauges 
that employ a freely sliding piston with none but un¬ 
avoidable retarding forces (such as friction) have 
been used. 

In one form, the gauge, in addition to the freely 
sliding piston, is provided with a rotating drum carry¬ 
ing recording paper on which a stylus attached to the 
piston writes. The resulting record is a plot of the 
integral of impulse versus time. Thus, the impulse at 
any time is proportional to the slope of the curve at 


that time, and the positive impulse is proportional to 
the maximum (positive) slope of the curve. The 
gauge records the negative impulse as well and, in 
principle, is capable of yielding a pressure-time curve 
by two differentiations with respect to time. This 
gauge has been designed and used by UERL. 41 

Another type of gauge embodying the same prin¬ 
ciple had been developed by RRL. 43 In this gauge, 
the piston is split into two parts. The outer part re¬ 
ceives on its surface the pressure of the blast, and 
pushes the inner section along the gauge. With the 
impulse thus acquired during the positive phase of 
pressure, the second part strikes a spring. The maxi¬ 
mum compression of the spring, which is proportional 
to the impulse given to the piston, is recorded by an 
indicating pointer and scale. In the suction phase, 
the first, or outer piston, is decelerated without affect¬ 
ing the motion of the second part, which is vented to 
allow free motion of air past it. 

Both types of free-piston gauge are quite precise 
and relatively simple to operate. The split-piston type 
gives a direct reading of positive impulse whereas the 
other gives records that must be interpreted by care¬ 
ful measurement. On the other hand, the records give 
more information concerning the blast wave. The 
principal disadvantage of the two gauges lies in their 
relatively complex mechanism. Another limitation is 
that the design of the gauge must be suited to the 
range of positive impulses that are expected, and the 
range for any one set of values of the mechanical vari¬ 
ables such as piston area and mass is not sufficiently 
wide to cover all likely possibilities. 

Damage Gauges 

Peak-pressure gauges have been devised to operate 
on the principle that a thin diaphragm, stretched over 
a hole in a rigid plate, will rupture at a certain pres¬ 
sure when the diaphragm is subjected to a blast wave. 
If several such diaphragms are provided, covering- 
holes of various sizes, the pressure required to rupture 
the diaphragm over a given hole will depend on the 
hole size. Hence, given a calibration of the device, the 
peak pressure of a blast wave is established as less than 
that required to break the diaphragm of the largest 
hole unbroken, and greater than, or equal to, the pres¬ 
sure required to break the diaphragm over the smallest 
hole broken. The pressure is thus bracketed as closely 
as is desired, simply by having a sufficient number of 
holes of graduated sizes. 

One such device, the paper blast meter, 44 has been 
used for many years in the approximate measurement 


CONFIDENTIAL! 





74 


EXPLOSIONS AND EXPLOSIVES IN AIR 


of blast pressures. It consists of two boards clamped 
together, with a sheet of paper held tightly between 
them. Holes of about ten different sizes are bored 
through both boards, in register. The gauge is 
mounted with the plane of the diaphragm perpendic¬ 
ular to the direction of propagation of the wave, i.e., 
head-on to the wave. By virtue of the multiplication 
of pressure on reflection, the pressure exerted on the 
diaphragm is greater than that of the incident wave; 
proper account of this must be taken. 

A more recent modification of this gauge is the 
foilmeter, which consists of a wooden or metal box 
with one open end over which is clamped an assembly 
similar to the paper blast meter but with aluminum 
foil instead of paper. Foil is used because it is much 
less sensitive than paper to changes in atmospheric 
conditions such as temperature and humidity. The 
box gauge can be oriented either face-on or side -011 
to the direction of propagation of the blast, since the 
box prevents the blast from acting on the reverse side 
of the diaphragm. The development, properties and 
use of foilmeters have been studied at the Princeton 
University Station 45 of Division 2. 

The great advantage of this type of peak-pressure 
gauge is its simplicity. The operation and the inter¬ 
pretation of results are simple, and 110 elaborate ma¬ 
chine work is involved. Its greatest limitation is that 
the precision of results is usually not high, and the 
limits within which the pressure can be bracketed 
with a reasonable number of holes are rather wide. 

A gauge based on the principle of bracketing the 
pressure between those required to move and not to 
move spring-loaded pistons was developed at the 
(British) ERL. A box containing six pistons sealing 
holes in its front face, each held in place by a spring 
with known force, constitutes the gauge. A slight mo¬ 
tion of a piston is detected by the displacement of an 
indicator piston, pushed by the first. In its present 
stage of development, this gauge is not capable of 
good precision. It also requires considerable machine 
work in construction. 

2 3 3 The Shock-Wave Velocity Method 

As was pointed out in Section 2.2.2 the shock-wave 
velocity is uniquely determined by the characteristics 
of the medium and the excess pressure in the shock 
wave. That is, under specified conditions, the pressure 
may be expressed explicitly in terms of the shock- 
wave velocity. (See Section 2.4.5, equation 8.) Advan¬ 
tage is taken of this relation to make very accurate 
measurements of peak pressures. 


The measurement of shock-wave velocity requires 
detectors, gauges, etc., which record the precise times 
of arrival of the wave at various known distances 
from the charge. In addition, it is usually desirable 
to measure the velocity of sound in the medium under 
identical conditions to those existing at the time of 
the principal velocity measurement. The acoustic ve¬ 
locity is measured conveniently by firing a small ex¬ 
plosive charge just prior to the firing of the main 
charge and observing the times of arrival of the acous¬ 
tic wave at the same gauges used for the main mea¬ 
surement. Thus the measurements required to obtain 
pressures from velocities are those of distance and 
time. Both, however, must be measured very accu¬ 
rately, since the percentage of errors in the computed 
peak pressures are several times those in the measured 
velocity. This system has been adopted as a routine 
measurement by BEL. 40 

The measurement of shock velocity as a means of 
obtaining peak pressure offers the great advantage 
that the true peak pressure can be obtained without 
the uncertainties associated with gauges which must 
be calibrated by methods which often do not well 
simulate the conditions of use. As was pointed out 
above, the necessary measurements are those of dis¬ 
tance and time. Very great accuracy of measurement 
of distance and time are required, especially at the 
lower pressures; because of the increased accuracy 
required, the jn’actical lower limit of pressure deter¬ 
mined by this method is about 3 psi; the complexity 
of apparatus required for velocity measurements is 
often as great as that for methods for obtaining pres¬ 
sure-time curves, and the latter method gives, in ad¬ 
dition to peak pressure, the positive impulse as well 
as other useful information. 

2,34 Other Experimental Methods 

The Photography of Explosion Phenomena 

The photography of explosion phenomena is a 
powerful experimental tool in this field. The detona¬ 
tion velocity, fragmentation processes, rate of expan¬ 
sion of the case, jets from hollow charges, the veloc¬ 
ity of the flame, etc., have been extensively studied 
by the Explosives Research Laboratory of Division 8. 
NDRC. (See the Summary Technical Report of 
Division 8.) 

The study of shock waves by photographic means 
has been a fruitful source of information. From flame 
velocities, the peak pressures very close to the charge 
have been obtained. 47 Shadow and sehlieren photog¬ 
raphy of the shock waves just outside the flame have 


confidential’* 







EXPERIMENTAL METHODS AND APPARATUS 


75 


produced information about the early stages of the 
expanding shock wave, particularly with regard to 
effects due to the shape of the charge. 48 Photographs 
of the shock waves at still later stages of their develop¬ 
ment have yielded information on their pressures, the 
nature of their reflections, the interactions of shock 
waves, etc. 49 ' 52 

For many purposes, such as the study of the action 
of structures under loading by blast waves, the most 
convenient apparatus is a high-speed motion picture 
camera with a continuous source of light. Such cam¬ 
eras are available commercially and provide frame 
speeds up to 8,000 frames per sec. Still higher speeds 
have been attained by special cameras. For some pur¬ 
poses, cameras using rotating mirrors 53,54 (with sta¬ 
tionary film) or rotatating drums 53,55 carrying the film 
have been developed. These cameras are particularly 
valuable for studying self-luminous phenomena, such 
as detonation waves and flame. 

Still pictures of shock waves can be taken by using 
an intermittent light source of very short intensity. 
Flashing lamps, 56 sparks, 49,51 and high-explosive 
charges 57 have been used as light sources. It is re¬ 
quired that the duration of the flash be sufficiently 
short that the motion of the shock during exposure 
is not so great as to blur the photograph unduly. The 
light source is ordinarily placed behind the shock wave, 
facing the camera lens, and either the shadow or the 
schlieren technique 58 is used. 

Another technique which has been of value in the 
study of shock waves, gas jets, etc., is that using in¬ 
terferometry. 59,60 In this method, the shock wave, 
jet, etc., which is being studied crosses one of two 
beams of an interferometer. Since the refractive index 
of the compressed air of the shock wave is different 
from that of the undisturbed air, the interference 
lines are caused to shift. Photographs of this phe¬ 
nomenon can be interpreted quantitatively in terms 
of densities of air in various parts of the domain pic¬ 
tured. The technique is particularly valuable, since 
it gives quantitative information, not only about the 
shock front but also about the region behind the shock 
front. 

The Measurement of Strain 

For measuring strains in objects subjected to the 
action of shock waves, a gauge consisting of a grid of 
resistance wire cemented between pieces of thin paper 
is very useful. The principle of operation has already 
been discussed. If a current is flowing through the 
wire when it is stretched or compressed, the potential 


across the wire will change as a result of the change 
in resistance caused by the strain in the wire. 61 (See 
Section 2.3.1). Such gauges are manufactured com¬ 
mercially. The paper and wire assembly is supplied 
cemented to a piece of felt cloth to facilitate han¬ 
dling. In use, the gauge is cemented to the surface of 
the object under test and is connected to the lead 
wires of the amplifying and recording apparatus. 
Oscillograms that can be interpreted as deflection¬ 
time curves are obtained. 

Aside from the quantitative measurement of strain 
in the material itself, the strain technique is valuable 
as an aid in establishing the chronology of events that 
accompany explosions. The interactions of blast waves 
with target structures can then be analyzed, with the 
purpose of establishing the mechanism of damage to 
the target. 

The Blast Tube 

A very useful apparatus for the study of shock 
waves in air and for the calibration of air-blast gauges 
is the blast tube. This device consists of a long tube 
which is divided into two sections, the compression 
chamber and the expansion chamber, by an air-tight 
diaphragm. Compressed air is admitted to the com¬ 
pression chamber to build up the required pressure, 
and when the diaphragm is punctured by a knife it 
shatters and a shock wave is formed which is propa¬ 
gated along the expansion chamber. Gauges can be 
mounted in the expansion chamber and their charac¬ 
teristics under conditions similar to those under 
which they are to be used can then be studied. The 
blast tube was devised at Princeton University Sta¬ 
tion. 20,49,62 ' 67 It has been used for gauge calibration 
by SOG 16 and by UERL. 13 

The relation between compression-chamber pres¬ 
sure and shock-wave pressure has been obtained theo¬ 
retically and experimentally. 63 ' 65 It was found that 
the experimental measurements lie about 6 per cent 
below those theoretically predicted. By inserting blocks 
into the compression chamber in order to shorten it, 
a shock wave can be produced whose pressure-time 
curve is very similar to those from explosive charges. 68 

The calibration studies of gauges in the blast tube 
reveal that the apparent gauge sensitivity decreases 
as the shock-wave pressure increases. This is inter¬ 
preted to be due to the disturbance of the air flow by 
the gauge, so that the average pressure on the sur¬ 
face of the gauge is less than that of the undisturbed 
wave. Theoretical computations have been made by 
the Applied Mathematics Panel, OSBD, 69 which 


CONFIDENTIAL’ 





76 


EXPLOSIONS AND EXPLOSIVES IN AIR 


show that the flow-effect hypothesis is reasonable. 

By means of a blast tube of rectangular cross sec¬ 
tion, the reflections of plane shocks at oblique angles 
have been studied by photographic technique. 49 (See 
Section 2.4.5.) 

24 ANALYSIS OF EXPERIMENTAL WORK 

2A.i The Criteria of Blast Damage 

The most conclusive way to test a weapon is to use 
it for its intended purpose, to do so many times, and 
to analyze and evaluate the results. b This is also the 
most expensive way to test it: the expenditure of lives, 
labor, and time may be very great, and the conse¬ 
quences of failure severe. The alternative is to deter¬ 
mine those characteristics of the weapon by virtue of 
which its purpose is accomplished, to formulate these 
characteristics in terms of simple, observable quanti¬ 
ties, and to measure those quantities under controlled 
conditions. 

Under certain conditions a high-explosive [HE] 
bomb, detonating near structures, will demolish or 
seriously damage them. The means by which the 
bomb accomplishes its purpose is its air blast; there 
may be contributions from fragments, earth shock, 
and the fires it may cause. In order to compare the 
effectiveness of two bombs, it is then necessary to 
measure their air-blast intensities under identical con¬ 
ditions. If all parameters (peak pressure, positive 
impulse, etc.) of the blast from one are more intense 
than the corresponding properties of the blast from 
the other, the result is established: the first bomb is 
superior to the second (for use in the open) provided 
a sufficient number of such comparisons establishes 
the statistical validity of the result. (In Section 2.4.6, 
comparison of explosives in enclosed rooms is taken 
up, and it is shown that under those conditions, the 
order of effectiveness of explosives is different from 
that in the open.) If some properties of the first bomb 
are superior and others inferior to those of the second, 
the result of the test is indeterminate, unless some 
further information is available on the basis of which 
it can be established that one property is more im¬ 
portant than another in the process of damage. For 
example, the fragment velocity from bomb A may be 
greater than that of B, and the blast peak pressure 
and impulse from B greater than those from A; if the 
bomb is to be used to accomplish blast damage, the 
superiority of the blast peak pressure and impulse 


from B would establish its superiority, other para¬ 
meters of A and B being of equal value. If, however, 
it were necessary to choose between two intensive 
properties of the blast, such as peak pressure and 
positive impulse, the choice would be very much more 
difficult. Fortunately, in most cases the order of supe¬ 
riority on the basis of positive impulse is the same as 
that of peak pressure. (See Table 2.) 

In order to obtain evidence that would establish 
the criterion of blast damage effectiveness of air-blast 
waves, careful studies 70 have been made by the Brit¬ 
ish of many bombing incidents in Britain during the 
blitz. By examination of bomb fragments, it was pos¬ 
sible to establish the size of bomb and to distinguish 
between bombs having explosive fillings containing 
aluminum and those which had nonaluminized fill¬ 
ings. 71 By this means the average area of damage 
was determined for each type of bomb, for each of 
four categories of damage: A (demolition) ; B (major 
irreparable damage) ; C (severe damage, requiring 
evacuation for a time) ; and D (minor damage, re¬ 
quiring only temporary evacuation). The mean radius 
for each type of damage was taken to be the radius 
of the circle whose area equalled the observed area 
of damage. 

Static detonation trials of similar bombs, with air- 
blast measurements, provided the necessary informa¬ 
tion on the peak pressure, positive impulse, etc., which 
would be obtained, on the average, at distances from 
the bomb corresponding to the radii of the four classes 
of damage. It was decided on the basis of such data, 
that for British buildings the mean radius of A dam¬ 
age corresponded to 120 psi-msec of positive impulse, 
B damage to 72, and C damage to 40. This implies, 
of course, that it is the positive impulse, and not the 
peak pressure, which is of principal interest in blast 
damage. Although this was the best that could be 
done under the circumstances, it was not entirely 
satisfactory, since the number of incidents analyzed 
was relatively small (72 in all), the range of bomb 
sizes was not great (1,000 to 5,000 lb), the exact 
nature of the filling was in doubt, and the scatter 
of the measurements of damage area was large, as 
would be expected. 

Proceeding on the basis of the 'positive impulse 
criterion so established, comparisons of bombs having 
various fillings were based principally on their rela¬ 
tive positive impulses. It was found experimentally 
that to a good approximation, the positive impulse 
depends on the reciprocal of the distance from the 
bomb; this implies, of course, that the radii of a given 


b See also Chapter 16. 






ANALYSIS OF EXPERIMENTAL WORK 


77 


category of damage from two bombs are proportional 
to the positive impulses from these bombs at a given 
distance, and hence that their areas of effectiveness 
are proportional to the squares of their positive im¬ 
pulses determined at a given distance. 

The early British air attacks on German targets 
yielded further information. It had been realized that 
the area of damage of a given bomb would be less with 
German targets than with British, because of the 
heavier average wall construction of German build¬ 
ings. Moreover, since the estimates of the effective¬ 
ness of these attacks depended on the interpretation 
of air-cover photographs, it was found that the dis¬ 
tinctions among the A, B, C, and D classes of dam¬ 
age could not be drawn, and therefore two classes 
were defined and adopted, (1) demolition (at least 
one-third of load-bearing walls destroyed) ; and (2) 
visible damage (damage visible on good quality, air- 
cover photographs). The corresponding positive im¬ 
pulses for the mean radii for these types of damage 
were estimated to be 120 and 55 psi-msec respec¬ 
tively. 

In the meantime, the development of heavier and 
heavier bombs progressed. The 4,000-lb high-capacity 
[HC] bomb was adopted very early and 8,000-lb and 
12,000-lb IIC bombs were soon developed. No such 
heavy bombs had been used by the Germans over 
England, and the extension of the incident studies, 
at best not conclusive, to such large bombs was not 
easily justified. Some experimental data were used 12 
on the response of brick walls to pressure and simpli¬ 
fying assumptions made, obtaining a result that in¬ 
dicated that for bombs greater in size than the 4,000- 
lb HC bomb, the positive impulse criterion was prob¬ 
ably no longer valid, and that, for bombs larger than 
the 12,000-lb HC, the peak pressure was probably 
of greater importance. Few bombs of these two larger 
sizes were used and they were sometimes mixed with 
other bombs and incendiaries. For these reasons, no 
very good test of the impulse criterion for very large 
bombs could be made from air-cover photographs. 
However, the few data which do exist 72 ' 74 support 
this prediction that for such bombs the criterion is 
neither purely impulse nor purely peak pressure but 
something between the two. 

More recently, a group composed of personnel from 
Divisions 2 and 11 of NDRC and from the Applied 
Mathematics Panel worked under directive AN-23 on 
the evaluation of the effects of weapons, both British 
and American, on targets. From careful analysis of 
strike and post-raid photographs, the mean area of 


effectiveness [MAE] of each of several types of bombs 
has been established. 75 (See Chapter 16.) 

For very large bombs, e.g., the atomic bomb, where 
the blast duration is very long (of the order of a 
second), there can be little doubt that the peak- 
pressure criterion holds. That is, for each target 
structure, a certain peak pressure is required to rup¬ 
ture the walls, and for predicting the area of damage 
to be expected it should be sufficient to know the 
distances from the bomb at which the peak pressures 
are just adequate. Theoretical consideration of the 
problem of reactions of structures under blast load¬ 
ing has recently been reported. 76 * 77 (See Chapter 15.) 

2,4,2 The Relative Effectiveness of 
Explosives in the Open 

The most common military high explosives that 
have been used or considered for use as fillings for 
aerial bombs are listed in Table 1, together with their 
chemical compositions and densities; the composi¬ 
tions of actual fillings vary by a few per cent from 
those given. Similarly, the filling density given for 
each explosive is an average over a number of actual 
filling densities in various batches. The importance of 
filling density is twofold: explosives are usually com¬ 
pared on the basis of equal volumes, so that the greater 
the density, the more favorable the comparative blast 
effectiveness. Second, the filling density is a measure 
of the quality of the particular filling; a poor pour will 
have air cavities and the components of the mixture 
will segregate. Both of these faults lead to low over¬ 
all densities. 

An important division of these explosives into two 
classes can be made: (I) those that contain alumi¬ 
num, and (2) those that do not. As can be seen from 
the relative blast intensities, the aluminum contrib¬ 
utes heavily to improved blast performance. 

The methods of comparing explosives on the basis 
of their air-blast intensities are essentially the same 
at all establishments where such work is done: the 
charges, consisting of identical containers filled with 
the explosives to be compared, are detonated while be¬ 
ing supported in a fixed position on the testing field. 
Air-blast gauges, usually electric, are set up at several 
distances from the charge, and blast pressure-time 
records obtained. From these records, the peak pres¬ 
sures and positive impulses are computed. The condi¬ 
tions of the test are held the same from round to 
round, so that direct comparisons among the different 
explosives can be obtained. The results are usually 
reported as relative peak pressures and relative posi- 


confidential! 






78 


EXPLOSIONS AND EXPLOSIVES IN AIR 


Table 1. Average densities and compositions of explosives. 


Composition,* per cent by weight of: 


Explosive 

Average 

loading 

density 

(g/cm) 3 

Ammonium 

nitrate 

Barium 

nitrate 

Ammonium 

pi crate 

Haleite 

PETN 

RDX 

TNT 

Aluminum 

i 

Wax 

Torpex (30% Al) 

1.74 

... 


• • • 



35 

35 

30 

• • • 

Torpex-2 f 

1.72 

. . • 





42 

40 

18 

0.71 

Minol-3 

1.71 

29 





... 

43 

28 

• • • 

DBX 

1.64 

21 





21 

40 

18 

• • • 

HBXf 

1.63 

• • • 





40 

38 

17 

5§ 

Tritonal 75 / 25 \\ 

1.72 

• . • 





. . . 

75 

25 

• . • 

Minol-2 

1.65 

40 





... 

40 

20 

• • • 

Tritonal 80/20 

1.70 

• • • 





... 

80 

20 

. • • 

Trialen 

1.64 

• • • 





15 

70 

15 

• • • 

Baronal 

2.14 

• • • 

50 




... 

35 

15 

• • • 

Comp. B 

1.61 

• • • 





60 

40 


It 

Pentolite 

1.60 

• • • 




50 

. . . 

50 


• • • 

Ednatol 

1.59 

• • • 



57 


... 

43 


• • • 

TNT 

1.56 

... 





... 

100 


• • • 

Picratol 

1.57 

• • • 


52 



... 

48 


. . . 

Amatex 

1.55 

44 





6H 

50 


• • • 

Amatol 60/40 

1.55 

60 





... 

40 


... 

Amatol 50/50 

1.55 

50 






50 


... 


*Under actual loading conditions, compositions vary by a few per cent from the average values given here. 

fWhen 0.5% calcium chloride is added to torpex-2, it is called torpex-3; HBX contains 0.5% calcium chloride in addition to its other ingredients. 
jNot taken into account in percentages of other ingredients. 

§D-2; desensitizing wax of the following composition: 6.9 parts Victory wax; 1.0 part nitrocellulose; 0.1 part lecithin. 

11 Also may include 2% carbon black. 

^Varies between 5% and 9%, at the expense of ammonium nitrate. 


tive impulses, referring all results to those from one 
type of lilling, chosen arbitrarily as a standard. Sev¬ 
eral identical rounds of each type of explosive are 
usually fired in each series of tests in order to estab¬ 
lish the statistical validity of the results. 

It is found that the relative pressures and impulses 
are essentially independent of the charge-to-gauge dis¬ 
tance, so that results obtained at a number of such 
distances can be considered as averages. Moreover, on 
the average, the results from various groups of experi¬ 
menters are in agreement. The average relative peak 
pressures and positive impulses for all explosives con¬ 
sidered are summarized in Table 2. These averages 78 
include results from trials in the United States by 
UERL and SOG, both of Division 2, NDRC, C and by 
BRL, Aberdeen Proving Ground, as well as in Great 
Britain, by RRL and ARD. All results are reduced to 
the basis of the average loading densities listed in 
Table 1. The adjustment to relative peak pressures and 

c Division 2, NDRC, reports dealing with the order of 
effectiveness of explosives and those of Division 8 which were 
transferred to Division 2 are given in references 79-92. A 
more complete bibliography of reports from all sources is given 
in reference 78. 


relative positive impulses for differences in weights 
was made according to the empirical formulas 



where P 1} P 2 are peak pressures from weights W lf 
W 2 respectively, and I x , I 2 are the corresponding 
positive impulses. For the usual variations in loading 
density, such corrections are of the order of 1 or 2 
per cent as a rule. 

A salient feature of the results in Table 2 is the 
sharp distinction between the aluminized and non- 
aluminized explosives: the aluminized explosives are, 
as a group, considerably superior to the nonalumi- 
nized ones. The increase in power is due to the high 
energy release of the oxidation of the aluminum. 
The chemical reactions in the detonation process have 
been studied theoretically. 93 

The addition of aluminum to explosives increases 
their bullet and impact sensitivity. (See Division 8, 
STR.) Because of this increased sensitivity, it was 
necessary to find some relatively insensitive alterna- 


ON FI 















































ANALYSIS OF EXPERIMENTAL WORK 


79 


tive to torpex-2. One explosive mixture whose sensi¬ 
tivity is satisfactory is HBX, which is made by the 
addition of D-2 wax to torpex-2. (See Table 1.) An¬ 
other effect of addition of D-2 wax to torpex-2 is to 
decrease the air-blast intensity, largely because of 
the decrease in loading density. A similar mixture is 
torpex D-l, in which the desensitizer wax used (D-l) 


Table 2. Peak pressure and positive impulse relative to 
those of Composition B (the comparison being on an 
equal volume basis). 


Explosive 

Relative 

peak 

pressure 

Relative 

positive 

impulse 

Torpex (30% Al) 

1.13 

1.21 

Torpex-2 

1.12 

1.15 

Minol-3 

1.09 

1.13 

DBX 

1.07 

1.11 

HBX 

1.06 

1.11 

Tritonal 75/25 

1.04 

1.10 

Minol-2 

1.06 

1.09 

Tritonal 80/20 

1.04 

1.08 

Trialen 

1.02 

1.06 

Baronal 

1.00 

1.02 

Comp. B 

(1.00) 

(1.00) 

Pentolite 

0.98 

0.97 

Ednatol 

0.94 

0.95 

TNT 

0.92 

0.94 

Picratol 

0.90 

0.90 

Amatex 

0.88 

0.85 

Amatol* 

0.86 

0.80 


’Applies to both amatol 60/40 and 50/50. 


is somewhat lower-melting than is D-2. No detectable 
difference exists in blast intensities between HBX 
and torpex D-l. It has recently become the practice 
to add 0.5 per cent of calcium chloride to torpex-2, 
HBX, and minol-2, in order to reduce the gassing 
that is produced in aluminized explosives. No effect 
on the air-blast intensities has been observed as a re¬ 
sult of the addition of calcium chloride. 

The relative damaging power of explosives can be 
estimated, for bombs that are not too large, on the 
basis of the positive impulse criterion (see Section 
2.4.1). Since the positive impulse has been shown to 
decrease linearly with increasing distance from the 
bomb, the relative damage radii are proportional to 
the relative positive impulse, and the relative areas 
of damage are estimated to be equal to the squares of 
the relative positive impulses. On this basis, and 
using data from Table 2, the bar graph in Figure 4 
was obtained. The heights of the bars are proportional 
to the estimated relative damage areas. The chief con¬ 
firmation of the improvement of aluminized over non- 
aluminized explosives comes from observations on the 
effectiveness of German bombs of both types in Brit¬ 



Figure 4. Estimated relative areas of damage based on 
relative positive impulse. 


ain. 71 In those incidents, the aluminized explosives 
(consisting of trialen or aluminized hexanite, both of 
which should be inferior to HBX and superior to 
TNT in blast intensity) gave 50 to 100 per cent more 
damage area than did the nonaluminized explosives 
(TNT or amatol 60/40). The estimated improvement 
from HBX, over the average of TNT and amatol 
60/40, would be about 65 per cent, which lies about 
midway between the observed values. 

The influence of several variables on the blast in¬ 
tensities of explosives has been studied: 

The Effect of Varying the Aluminum Content in 
Torpex, Minot, and Tritonal-like Compositions. Al¬ 
though torpex-2 contains 18 per cent aluminum, 
minol-2 20 per cent, and tritonal 20 per cent, these 
are not the aluminum concentrations that give the 
greatest blast intensities. By experiments with mix¬ 
tures containing various percentages of aluminum, it 
has been shown that the optimum compositions con¬ 
tain: torpex, 30 per cent; 94 minol, 28 per cent; 95 ' 96 
and tritonal, 25 per cent. 97 ' 100 As a result of these 
experiments, the British proposed to replace minol-2 
and ordinary tritonal by minol-3 and tritonal with 
25 per cent aluminum. (See Table 1.) 

The Effect of Aluminum Grain Size on Blast In¬ 
tensities. There are two reasons for the interest in 
the effect of aluminum grist size on blast intensities. 
(1) Because of mass-production processes for “atom¬ 
izing” aluminum, some grists were in better supply 
than others, and (2) it was found 101 that use of the 


^CONFIDENTIAL 







































80 


EXPLOSIONS AND EXPLOSIVES IN AIR 


coarser grists produced less sensitive explosives. Ac¬ 
cordingly, tests were performed which showed that 
aluminum powder that passed a 50-mesh sieve and 
was retained on a 150-mesh sieve could be used in 
place of the Navy specification aluminum (30 per cent 
of which passed a 325-mesh sieve) in torpex without 
loss of power, 87 but with considerable gain 101 in 
insensitivity. Also, it was found 102 that minol-2, 
prepared from “36-mesh to dust” aluminum was 
equal in power to that prepared from “200-mesh to 
dust” material. 

Effect of Bomb Case-Weight on the Order of Merit 
of Explosives. Static detonation trials of both alumi¬ 
nized explosives in the forms of “bare” and cardboard- 
cased charges and heavy-, medium-, and light-cased 
bombs showed no dependence, on the average, of the 
relative blast intensities on case-weight. 78 

Dependence of Order of Merit on Distance from 
the Bomb. On the average, the experimental evidence, 
based on blast-pressure measurements made over 
ranges of charge-to-gauge distance corresponding to 
pressures of most importance in producing damage, 
shows the relative peak pressure and relative positive 
impulses to be independent of distance. 78 Other ex¬ 
perimental work, 103 however, indicates that, for very 
small distances from the charge, the order of merit 
may be very different from that in the range of dis¬ 
tances wherein air-blast measurements are usually 
made. 

243 The Principle of Similitude 

By dimensional reasoning, the following principle 
of similitude was derived for explosions and explo¬ 
sives. If, of two charges of the same explosive, all of 
the dimensions of one are Jc times those of the other, 
the peak pressures measured at any distance from the 
smaller will be equal to those measured at k times 
that distance from the larger. Moreover, the positive 
impulse, energy, positive duration, etc., from the 
larger will be k times the corresponding quantities 
for the smaller, the distances from the charge being 
in the proportion k/1. This principle, of course, as¬ 
sumes that all other variables not so specified are the 
same in the two cases. The principle of similitude is 
not necessarily inviolate; it has required experimen¬ 
tal verification. 

The principle may be restated in terms of the 
weights of the charges, since the densities are pre¬ 
sumed to be equal. If the weights of two geometrically 
similar charges of the same explosive are W x and W 2 , 
the peak pressures at distances proportional to ^W 1 


and ^ IT 2 , respectively, will be equal and the posi¬ 
tive impulses, durations, etc., will be proportional to 
il/W 1 and W 2 , respectively, at those distances. 

This can be expressed as follows: 


W= F (lfr) 

and 

(3) 

where F, I, and t c are the peak pressure, positive im¬ 
pulse, and positive duration, respectively, measured 
at a distance r from IF pounds of explosive, and /, F, 
and (f> are unspecified functions of the variable r/WK 

The similarity law as applied to air blast has not 
received an adequate test. For a range of charge 
weights from 8 to 550 lb, it has been found that the 
principle of similitude is applicable within limits of 
error of a few per cent. 104 By taking into account 
the effects of the case of bombs, differences in explo¬ 
sives, etc., it was shown 105 that the principle was 
applicable to blast measurements made by BRL on a 
range of charge sizes from 100- to 10,000-lb bombs. 
However, it has been found by British investigators 
that the positive impulses from 66-lb bare charges of 
Composition B 106 give values, predicted for 4,000-lb 
bombs by the similarity principle, that are consider¬ 
ably less than those actually obtained, the effect of 
the case being taken into account. Moreover, blast- 
pressure measurements at UERL, using very small 
bare charges, of the order of 2 to 4 lb in weight, lie 
well below those obtained elsewhere for larger charges 
of approximately the same shape. In order to test the 
principle properly, charges ranging in weight from 
1 to 10,000 or 100,000 lb, and having identical shapes, 
explosive fillings, types of case, etc., should be de¬ 
tonated and blast-pressure measurements made under 
the same conditions by several investigators. 

There are several quite reasonable qualitative argu¬ 
ments which would deny the exact applicability of the 
principle of similitude. 

The Lack of Similarity of Afterburning. After¬ 
burning, which was described in Section 2.2.1, is a 
term applied to the relatively slow combustion of the 
products of the chemical reactions in the detonation 
process, and involves the reaction of combustible 
products (carbon monoxide, hydrogen, methane, car¬ 
bon, etc.) with atmospheric oxygen. That this process 


4 OX.FIDE2JTIAI4 














ANALYSIS OF EXPERIMENTAL WORK 


81 


actually does occur lias been demonstrated experi¬ 
mentally. 107,108 

If this process (afterburning) occurs only at the 
periphery of the globe of hot gases, the extent of the 
reaction is determined by the area of the globe (ap¬ 
proximately spherical). This means that the relative 
importance of the afterburning reaction would de¬ 
crease with increasing charge-weight, since the ratio 
of area to volume of a sphere decreases linearly with 
increasing radius (i.e., charge-weight). 

On the other hand, if mixing of atmospheric oxy¬ 
gen with the hot detonation products takes place, the 
burning is a volume and not a surface phenomenon. 
Since the elapsed time for a given process (e.g., ex¬ 
pansion of the hot gases to a certain pressure and 
temperature state) is proportional to the cube root 
of the charge-weight (to a first approximation) the 
extent of a chemical reaction within the gas globe 
which has a finite reaction rate will be greater for 
longer elapsing time and the energy liberated will, 
therefore, be greater. By this mechanism, larger 
charges would be expected to give greater energies 
per unit weight of explosive. It has already been men¬ 
tioned that the energy available from complete com¬ 
bustion of an explosive is of the order of three times 
that available from its detonation alone. Therefore, 
afterburning, at least in principle, may give rise to 
large departures from the principle of similitude. The 
scanty experimental evidence available indicates de¬ 
partures from the similarity principle in the direction 
predicted by this argument. 

The Skin-Effect. If a sphere of explosive is deto¬ 
nated at its center, a spherical detonation wave, con¬ 
sisting of a chemical reaction zone of high tempera¬ 
ture and pressure preceded at a small distance by a 
shock wave, will be propagated outward from the 
center of the charge. On reaching the surface of the 
charge (presumed to be unconfined, in air), the shock 
wave is reflected inward as a rarefaction. This rare¬ 
faction, or tension wave, will shortly meet the advanc¬ 
ing chemical reaction zone and should tend to “freeze” 
the reactions by lowering the temperature and pres¬ 
sure in the reacting material. Thus a thin “skin” of 
undetonated explosive will be ejected from the charge, 
and the energy available will not be fully realized. 
Now the thickness of the skin is independent of the 
size of the charge; therefore, the fraction of the total 
weight of explosive which is in the skin decreases 
with increasing charge-weight. As a result of the skin- 
effect, departures from the similarity principle would 
be expected, and in a direction such that the blast in¬ 


tensity should increase disproportionately with in¬ 
creasing charge-weight. However, this effect should be 
most pronounced for very small charges, and should 
be negligible for large charges. 

The presence of a heavy metal case around the 
charge would alter the phenomenon: on reaching the 
interface between metal and explosive, the shock wave 
is partly reflected as a compression, and partly trans¬ 
mitted as a compression in the metal. If the rarefac¬ 
tion wave reflected from the metal-air interface fails 
to meet the oncoming reaction zone before it has 
reached the metal, no skin-effect would be expected. 

It is obvious that experimental work is required to 
test these hypotheses. For practical purposes, and 
over moderate ranges of charge size, the similarity 
principle can be applied, for want of more direct ex¬ 
perimental results. 

2 4 4 The Effect of a Case on the Blast 
Intensity from an Explosive Charge 

It was pointed out in Section 2.2.1 that if the 
explosive charge is contained in a metal case, as in 
a bomb, the expansion, rupture, and projection of 
fragments of the case require energy which can come 
only from the energy released in detonation. This 
subtraction of energy reduces the amount that is 
available for the shock wave, and, therefore, shock- 
wave intensities from a cased charge are less than 
from a bare charge having the same net charge-weight. 

A series of experiments using 8-lb charges of Com¬ 
position B encased in cylindrical containers of vari¬ 
ous thicknesses was performed by BRL. 109,110 These 
results showed that both peak pressure and positive 
impulse from the explosive charge are reduced by the 
case, and that the reduction is greater, the greater the 
case thickness. It has been shown that the empirical 
equation , . 



expresses ERL results within experimental error. 
Here I 1 and I 2 are the positive impulses from the 
cased and bare charges respectively, 17 and W c are 
the weights of the explosive charge and total weight 
of cased charge, respectively, and e is the base of 
Naperian logarithms. 

By making simple assumptions 105 about the par¬ 
tition of energy between shock wave and fragments, 
a somewhat different expression was derived from the 

II" = ( 0.2 + - + ul j W ) IT, (5) 


Confidents 










82 


EXPLOSIONS AND EXPLOSIVES IN AIR 


where W is the explosive charge-weight in a cased 
charge whose equivalent case-weight is M, and IF' 
is the bare charge-weight whose blast pressure and 
impulse would be identical to those of the cased 
charge. However, it happens that both expressions 
give very nearly equal numerical results. The second 
expression has the advantage that it predicts the effect 
of case-weight on peak pressure as well as on positive 
impulse. The effect of case-weight on peak pressure 
and positive impulse are shown graphically in Figure 
5 in terms of the weight of bare charge required to 
give equal blast intensity to that of a cased charge. 
For use in equations (4) and (5), the charge-weight 
ratio [W/W e of (4), W/(M+W) of (5)] is the 
“equivalent” charge-weight ratio, obtained by comput- 



Figure 5. Effect of case weight on peak pressure and 
positive impulse. 


ing the ratio of charge-weight to total weight for a 
hypothetical cylindrical charge having the same 
weight as the charge-weight in the bomb, the same 
diameter as the cylindrical section of the bomb, and 
the same case thickness as that on the cylindrical 
section of the bomb. This amounts to assuming that 
the casing of the ogival nose and conical tail sections, 
which are relatively heavily cased, detract relatively 
little from the overall blast from the bomb, at least 
as far as measurements perpendicular to the bomb’s 
equator are concerned. Table 3 lists “equivalent” and 
“actual” charge-weight ratios for some American and 
British bombs. 112 

Further evidence of the pronounced effect of the 
case-w'eight on blast pressures and impulses lies in a 
comparison of the blast from 500-lb general-purpose 


Table 3. Charge-weight ratios of American and British 
bombs. 112 R = charge-weight ratio. 


Bomb 

R (per cent) 
Equivalent cylinder 

Actual 

American bombs 

100-lb GP 

0.67 

0.50 

250-lb GP 

0.61 

0.50 

500-lb GP 

0.65 

0.51 

1,000-lb GP 

0.59 

0.56 

2,000-lb GP 

0.64 

0.53 

500-lb SAP 

0.36 

0.31 

1,000-lb SAP 

0.34 

0.32 

1,000-lb AP 

0.25 

0.14 

4,000-lb LC 

0.82 

0.80 

British bombs 

250-lb GP 

0.40 

0.29 

500-lb GP 

0.37 

0.31 

1,000-lb GP 

0.43 

0.33 

4,000-lb GP 

0.38 

0.30 

250-lb SAP 

0.21 

0.17 

500-lb SAP 

0.20 

0.18 

500-lb MC 

0.54 

0.41 

1,000-lb MC 

0.62 

0.47 

4,000-lb MC 

0.60 

0.58 

2,000-lb HC 

0.81 

0.72 

4,000-lb HC 

0.80 

0.75 

8,000-lb HC 

0.75 

0.68 

12,000-lb HC 

0.75 

0.67 


[GP] bombs and 350-lb depth bombs 88 and in the 
comparison of the blast from aluminum and thin 
steel cased bombs with those from bombs of standard 
case thickness. 113 ' 116 

The important implication of these results is that 
a large blast bond) should have the minimum weight 
of metal casing consistent with safety in handling the 
bomb. For such a bond), the best fuzing is proximity 
variable-time [YT] fuzing; there is no danger of 
breakup of a thin case, since the bomb functions 
either in mid-air or instantaneously on impact. The 
minimum case thickness is, therefore, that necessary 
to avoid injury to the bomb in handling prior to the 
attack. 

The improvement in blast performance obtainable 
with thin steel or aluminum cases over the standard 
bombs is illustrated in Table 4, where relative areas 
of damage from a fixed quantity of explosive encased 
with various thicknesses of metal and from equal 
total weights of bombs of various case-weights are 
estimated, using the positive impulse criterion. (See 
Section 2.4.1.) It should be emphasized that experi¬ 
ment shows no significant difference in the effect of 
a case for various explosive fillings. Hence, improve¬ 
ments obtained by reducing the case-weight are in 
addition to improvements obtained from better explo¬ 
sives (see Section 2.4.2) or by proximity fuzing (see 
Section 2.4.5). 


• •' \ ) 'KNT! \l 

































ANALYSIS OF EXPERIMENTAL WORK 


83 


Table 4. Estimated relative areas of damage from 
bombs of various case thicknesses.* 


A. Charge-weight equal for all bombs. 


Type of bomb 

Total weight 
Wt of charge 

Equivalent 
cylinder 
C/W ratio 

Estimated 
relative 
damage area 

Bare charge 

1.00 

1.00 

1.00 

Aluminum case 

1.10 

0.93 

0.88 

Thin steel case 

1.15 

0.90 

0.83 

LC bomb 

1.25 

0.82 

0.71 

GP bomb 

1.88 

0.64 

0.49 

B. Total weight equal for all bombs. 



Equivalent 

Estimated 


Charge weight 

cylinder 

relative 

Type of bomb 

Total weight 

C/W ratio 

damage area 

Bare charge 

1.00 

1.00 

1.00 

Aluminum case 

0.90 

0.93 

0.76 

Thin steel case 

0.87 

0.90 

0.69 

LC bomb 

0.80 

0.82 

0.53 

GP bomb 

0.53 

0.64 

0.21 


*The same type of explosive filling is assumed throughout. 


Reflection of Shocks and the 
Mach Phenomenon 


The Rankine-Hugoniot Equations 

Relations (the Rankine-Hugoniot equations) that 
express the application of the laws of conservation of 
mass, momentum, and energy to a shock wave are 


p (U — u) = po U, 

V Po pol tx, . ^ v 

^ — i (P + Vo) (- j, (6) 

\Po P / 

where U is the velocity of the shock front, p , p, u are 
the density, pressure, and particle velocity behind the 
shock, p 0 , p 0 are the corresponding quantities in the 
undisturbed medium in front of the shock, and A E 
is the change in energy content in crossing the shock 
front. All pressures are absolute, not gauge, pressures. 

These equations can be combined to produce the 
following explicit dependence of the velocity of propa¬ 
gation U on the pressure in the shock p and the pres¬ 
sure p 0 and velocity of sound c Q in the undisturbed 
medium (a perfect gas) 



where y is the ratio of specific heats at constant pres¬ 
sure and constant volume. For air, at pressures (and 
corresponding temperatures) not exceeding 300 psi, 
y is very nearly constant and equal to 1.40. The 
velocity-pressure relation for air for these pressures 
then becomes: 


p = 7 U 2 1 

p 0 ~ 6 c 0 2 6 



As pointed out in Section 2.3.3, this equation is the 
basis for a very accurate method for determining peak 
pressures. For temperatures corresponding to pres¬ 
sures higher than 300 psi, y ^ 1.40; the properties 
of air to 15000 K have been computed and tabu¬ 
lated. 117 


Head-on Reflection of Shocks 

The reflection of shocks from plane surfaces was 
briefly described in Section 2.2.3; a more detailed 
analysis is presented below. 

When a shock strikes a plane reflecting surface 
head-on, the properties of the reflection phenomenon 
obey not only the Rankine-Hugoniot equations, but 
the added requirement that no matter can cross the 
boundary between the surface and the gas. Hence, the 
particle velocity behind the reflected shock as it leaves 
the surface must be zero with respect to the wall. 
Figure 6A d depicts a plane incident shock I just 


<D 


P, P. u, e 
U 


A ® 

P,.P 0 - u o *°< c o 

777777777777777777 



u, c 


B © 

lit t 

p,p,u«o,c 

7777777/777777/7777 


Figure 6. Reflection of shock from plane surface. 
A. Incident shock before reflection. B. Shock after 
reflection. 


before striking a wall IF. In the region B, behind 
the shock, the pressure, density, particle velocity, 
and velocity of sound are p, p , u, and c, respectively, 
and the corresponding quantities in front of the shock 
(i.e., in the undisturbed medium A) are p Q , po , u Q = 
0 and c 0 , respectively. Upon striking the wall, the 
shock R is reflected and travels away from the wall 
into the compressed region B. The pressure, density, 
and local velocity of sound behind the reflected shock 
(i.e., between R and IF in the region C) are denoted 
by p', p', c f . The particle velocity v! equals zero, as 
mentioned above. 

The pressures in the regions A and C are related to 
the pressure in B by: 


It should be noted that 

is 1 * ? a!• 

By application of equations (6), and assuming an 
ideal gas, the compression ratio £' of the reflected 

d The figures and notations are due to von Neumann whose 
exposition of this subject is particularly clear. 


COXFIDE .VTI.A \J 



























84 


EXPLOSIONS AND EXPLOSIVES IN AIR 


shock can be obtained in terms of that of the incident 
shock t 

■ o) 


(y + i) £ + (y — i) 


Again y refers to the ratio of specific heats at con¬ 
stant pressure and at constant volume. If y is taken 
to be constant and equal to 1.40 over the whole range 
of pressure, it can be seen that 

1 ^ £' ^ 8, when 1 ^ 0 . 

That is, according to their relation for very strong 
incident shocks, the pressure in the reflected shock may 
be as much as eight times as great as the pressure in the 
incident shock. For very weak shocks, the excess pres¬ 
sure ( p' — p 0 ) in the reflected shock is about double 
that in the incident shock (p — p Q ). However, for very 
strong shocks in air y ^ 1.40, and it is no longer 
possible to get an accurate solution using the approxi¬ 
mation assuming air to be an ideal gas. 


Oblique Reflection of Shocks : 

Regular Reflection 

The theory of the oblique reflection of shocks from 
plane surfaces has been presented. Consider an inci¬ 
dent plane shock I which meets a wall W at an angle 
a. (See Figure 7.) A reflected shock R is formed at 
the wall at some angle oc\ With notation similar to 



Figure 7. Oblique reflection of shock from plane surface. 


that of the previous section, A, B, C are the domains 
in front of the incident shock, between the two shocks, 
and behind the reflected shock, respectively. The gas 
in these domains has pressures p Q , p, p', densities po , 
p, p', and local sound velocities c 0 , c, c' , respectively. 
The velocity of propagation of the incident shock with 
respect to the gas in A is U, and that of the reflected 
shock, also with respect to the air in A, is 77'. If the 
frame of reference is taken fixed with respect to the 
line of contact with the wall T , gas can be considered 
as flowing into the shock with the velocity 2 . This 
flow is turned (in the direction x) by the oblique 
shock I and its velocity is changed. Since there can 
be no component of flow normal to the wall, behind 
R, the strength of R and the angle a' must be such 


that the flow is again turned parallel to the wall in 
the direction z'. 

By application of the Rankine-Hugoniot equations 
and ideal gas laws to the above simple geometrical 
picture, the strength and angle of a' of the reflected 
shock R have been computed as functions of the 
strength of 7 and its angle. 118,119 Several remarkable 
properties of obliquely reflected shocks are predicted 
by this theory. 

1. For a given strength of incident shock (measured 
by £,), there is some angle of incidence a ex treme such 
that the type of reflection described above cannot 
occur for a > a ext reme. 

2. For each gaseous medium, there is some angle 
a 1 such that for a > <x 1 the strength of the reflected 
shock is greater than it is for head-on reflection. For 
air (approximated as an ideal gas with y = 1.40) <x 1 = 
39° 23'. 

3. For a given strength of incident shock, there is 
some value for a = a min such that £' is a minimum. 

4. The angle of reflection <z' is an increasing mono¬ 
tonic function of the angle of incidence a. For a oq, 
a' ^ a and for a = a ex tremej a' > c. 

These properties of obliquely reflected shocks of 
finite strength (£ < 1) may be contrasted with cor¬ 
responding properties of acoustic waves (in which 

( = O- 

1. Acoustic reflection occurs for 0 a < 90°. 

2. £ = g for all values of a. 

3. Same as 2. 

4. a = a' for all values of a'. 

The theory of regular reflection received exhaustive 
tests in experiments at the Princeton University Sta¬ 
tion. 49 A “shock tube/’ consisting of a pipe of rec¬ 
tangular cross section partitioned by a destructible 
diaphragm, was employed. (See Section 2.3.4.) In one 
section, the compression chamber, compressed air was 
admitted to build up the desired pressure. In the 
other section, the expansion chamber, the air was at 
atmospheric pressure or below it. When the diaphragm 
was punctured, it was shattered, and a plane shock 
wave was propagated through the expansion chamber. 
A “wall,” which could be set at any desired incidence 
with the shock wave, was held firmly in the expansion 
chamber. By means of transparent windows, the shock- 
wave system and the wall were photographed in pro¬ 
file, using a spark as a light source. Shock strengths 
were computed from measured shock velocities. 

The theory of regular reflection was verified for a 
wide range of pressures and angles of incidence. The 


U-M IhKNTlAl* 









ANALYSIS OF EXPERIMENTAL WORK 


85 


prediction that no two-shock (i.e., regular) reflection 
could exist abovea = a ext reme was quantitatively con¬ 
firmed. 

Mach Reflection 

In a series of papers, E. Mach 121 ' 123 and collabo¬ 
rators reported experiments on the interaction of shock 
waves arising from intense sparks. 120 ' 124 Their ex¬ 
periments were as follows. To a glass plate, tinfoil 
electrodes were cemented, so that one or more sparks 
from a battery of Leyden jars would follow preset 
patterns on the glass surface. Parallel with the first 
plate and a few millimeters from it a second plate was 
supported, coated on its inner surface with soot. When 
a spark occurred, the soot just opposite it was blasted 
clear of the plate. They observed that if the electrodes 
were so arranged that two sparks, one long (the linear 
spark), the other quite short (the point spark), oc¬ 
curred simultaneously, not only was the soot cleared 
away opposite the sparks themselves, hut a thin line 
of soot was deposited between the point and line sparks 
in the shape of a parabola, the point being the focus, 
the line the directrix. The line of soot was inter¬ 
preted to be the locus of intersection of the plane and 
cylindrical shocks from the two sparks. However, at 
the two ends of the parabolic line, the line broadened 
into fans or P’s, regions from which soot was partly 
cleared. This is called the Mach Y-ausbreitung, or 
simply the Mach V. 

Experiments of this type were repeated 125 at Har¬ 
vard in 1941, particular attention being directed to 
study of the V. Using an arrangement similar to 
Macids, with an “angular” spark S (angle between 
two sparks = 2a) and a linear spark S' opposite the 
angle, it was found that with angles less than 2a = 

S 2 I s ' 



Figure 8. Illustrating shock waves from intense 
sparks (Mach F). 


110°, no V was formed, but that a ridge of soot bisect¬ 
ing the angle was formed instead. As 2a was in¬ 
creased over 110°, a V was formed, and the angle 
(2</>) of the V was found to increase as a was in¬ 
creased. (See Figure 8.) Moreover, lines 1, Y, 2, 2', 
and 3 were observed in the soot. Lines 1 and Y were 
obviously the loci of intersection of the shocks from 


R I 



S and S' lying above and below the axis of symmetry, 
respectively, and 2 and 2' were thought to be loci of 
intersection of the portions of S and S' on opposite 
sides of the axis of symmetry. In the V region, only 
one shock, 3, was observed. 

Similar experiments were performed 126 with re¬ 
fined technique, and photographs were obtained show¬ 
ing the instantaneous picture of the shock system 
from an angular spark. Photographs of three-shock 
systems involving shocks related to 1, 2, and 3 in 
Figure 8 have been obtained by many investigators. 
The reflection was photographed 51 of shocks arising 
from explosive sources; reflection of the bow waves 
of projectiles in flight from plane surfaces was photo¬ 
graphed at BRL. e 

It was pointed out above that regular (i.e., two- 
shock) reflection cannot occur at angles a > a ex treme- 
Some other shock system must replace it; such a sys¬ 
tem is the three-shock system composed of the inci¬ 
dent /,reflected I?,and Mach M shocks (seeFigure 9) . f 

It has been demonstrated experimentally 49 that, 
in addition to the three shocks I, R, and M there is a 
“slipstream” S, which is a boundary between regions 
of different particle velocity and different density 
but of the same pressure. It was also found that, when 
a > ^extreme? a Mach wave ill is formed at the wall 
which grows as the shock system moves along the 

e Work of A. C. Charters and R. N. Thomas of BRL. 

* Note that one can think of obtaining the configuration of 
Figure 8 (i.e., intersection of shocks) by removing the wall IF 
in Figure 9 and replacing it by the mirror image of the shock 
system above the wall. 


O'Nhukn i; \ f-t 













86 


EXPLOSIONS AND EXPLOSIVES IN AIR 


wall, and the locus of the triple point T is a straight 
line, l — l. 

The theory for Mach configurations in shock sys¬ 
tems is only partly developed. A number of work- 
ers ii 9 ,127-130 recen tly have contributed to the pres¬ 
ent state of its advancement. However, there is a large 
body of experimental work on the Mach wave system, 
and empirical correlations have been found which 
make the results very useful for practical military 
purposes. 

The Application of Oblique Reflection in 
Air-Burst Bombs 

The proposal that the effectiveness of bombs might 
be increased if they were detonated at some height 
above the ground, rather than on the ground, was ad¬ 
vanced early in the war. However, the properties of 
oblique and Mach reflection were not understood at 
that time, and the improvement in performance was 
supposed to arise from a reduction of the screening 
effect of one building on another. A model town was 
built of brick, earth, and heavy timbers, and blast 
measurements were made 131,132 by RRL with gauges 
located among the buildings and charges detonated 
at various heights above the streets. The results indi¬ 
cated that peak pressures were considerably greater 
from a charge burst at the optimum height than from 
a ground-burst charge, and that the area of damage 
of the B category could be more than doubled by air 
burst, if the impulse criterion was assumed to apply. 
(See Section 2.4.1.) The optimum height for maxi¬ 
mizing B damage from 4,000-lb bombs was taken to 
be 200 ft ( a figure later shown to be much too great). 

A number of 4,000-lb HC bombs were provided 
with proximity fuzes, set to function at about 200 ft 
above the ground, and were dropped in British raids 
over Mayen and Spezia. For a number of reasons, only 
a few of the bombs functioned properly over appropri¬ 
ate target areas, with interpretable post-raid air-cover 
photography. These incidents were evaluated and it 
was decided that, since the two bombs (out of 10 
dropped) which could be located and which func¬ 
tioned properly at 190 ft above ground level gave less 
demolition, but twice as much visible damage as 
would impact-burst bombs, the performance did not 
justify its introduction into service. This decision, of 
course, was based on three misconceptions: (1) that 
shielding, or rather the absence of shielding, was solely 
responsible for increased damage area; (2) that the 
optimum height of burst should be 200 ft (instead of 
40 to 70 ft as was later demonstrated) ; and (3) that 


demolition could not be increased, but only reduced 
by air burst. It is, however, surprising that so impor¬ 
tant a decision was made on such poor grounds; the 
performance of two bombs was the whole basis for the 
decision. In spite of this, in the light of later experi¬ 
mental evidence, the performance of the bombs was 
just what would be expected from a burst so high 
above the optimum. 

In 1943, it was urged that the blast-measurement 
groups at UERL and Princeton undertake further 
studies of the properties of air-burst charges, and this 
time, the basis of the proposal was not shielding, but 
the properties of obliquely reflected shock waves, even 
in the absence of a built-up area. In December 1943 
there was begun at UERL a study of the effect of 
height of burst on the peak pressures and positive im¬ 
pulses in the blast, measured at a few set horizontal 
distances from a small charge detonated at various 
heights above the ground; 134 ' 138 gauges were placed 
at a few heights above the ground. Somewhat earlier, 
the Princeton University Station had undertaken sim¬ 
ilar studies, with several gauge-to-charge distances, the 
gauges being mounted flush with the ground. 139 ' 144 
The work 49 using the shock tube with a photo¬ 
graphic technique that was described above was also 
begun in this period. The UERL work, in collabora¬ 
tion with SOU included cardboard-cased charges of 
2-, 12-, and 42-lb weight; that of Princeton Univer¬ 
sity Station included largely ^-lb TNT engineer 
blocks. All results were in agreement: as the height of 
burst was increased, the peak pressure and positive im¬ 
pulse measured at a fixed horizontal distance in¬ 
creased to maximum values and then decreased. The 
height of burst required to produce a maximum area 
of specified damage, i.e., the optimum height of burst, 
depended to some extent on the magnitude of the 
peak pressure or positive impulse of the area of which 
it was desired to maximize. For demolition-type dam¬ 
age, the height of burst was such that the range of 
heights at the optimum for a 4,000-lb light-cased 
[LC] bomb was estimated to be 40 to 70 ft. The maxi¬ 
mum (particularly for positive impulse) was found to 
be so broad that the optimum height was not critical: 
variations from it of as much as ±20 per cent pro¬ 
duced within 10 per cent of the optimum positive 
impulse. 

Finally, these studies were followed by full bomb- 
scale tests. UERL and SOU measured the blast from 
bombs ranging in size from 350-lb depth bombs to 
2,000-lb GP bombs supported at various heights above 
the ground. 145 ' 147 The earlier small charge results 


i'i >\ i'l I 'KNT! A li 






ANALYSIS OF EXPERIMENTAL WORK 


87 


were confirmed and the increase in area of damage 
from air-burst over impact-burst bombs was predicted 
to be 50 to 100 per cent. The UERL work is sum¬ 
marized 88 and an empirical method for express¬ 
ing the results by means of a few parameters is 
reported. 148 

In the meantime, when British investigators learned 
of the early HEEL results, the question of air burst 
was reopened and the assessment of the raids on 
Mayen and Spezia was re-examined. 149 It was con¬ 
cluded that the burst at 200 ft gave B damage slightly 
less than for ground burst, and about twice as much 
less serious C damage, and that the Spezia incident 
was fully in accord with the model town experi¬ 
ments. 131 When the Static Detonation Committee 
compared 150 the early UEEL and ERL 131 results it 
concluded that they were broadly in agreement. A 
commentary 151 was issued which stated the history 
of the British experience and reconciled it with UERL 
results. Additional information about the effect of air- 
burst bombs was obtained from V-l bombing incidents 
in Britain. 152 

Two new series of blast measurements on air burst 
were undertaken in England. In one, 67-lb bare 
charges of Composition B were detonated at various 
heights above the open ground, with gauges at various 
distances from the charge and at two heights above 
the ground. 153 These results were in fair agreement 
with the previous work at UEEL and Princeton Uni¬ 
versity Station. Quantitative differences in the mea¬ 
sured quantities among the results of the four labora¬ 
tories were found, and although these have not been 
fully explained to date, all results are in approximate 
agreement in the optimum heights of burst and the 
magnitude of the increased effectiveness to be expect¬ 
ed. In a second series of trials 1,34 a one-seventh 
scale model town was constructed and 8-lb charges 
of Composition B were fired at various heights above 
streets and buildings, with gauges recording the blast 
at various points in the city. These experiments con¬ 
firmed the earlier work in that blast pressures and 
impulses were found to he maximized by air burst. 
Moreover, the presence of buildings did not alter this 
advantage. Earlier work 137 had also shown that the 
increases in effectiveness due to air burst could be ob¬ 
tained with obstacles in the path of the blast. 

The general subject of “Air Burst for Blast 
Bombs” 1 was treated at a symposium in Washington, 
D. C., sponsored by Division 2, NDRC, for the pur¬ 
pose of presenting the subject to representatives of 
the Services. The topics included an introductory ex¬ 


planation, the experimental background, the inter¬ 
pretation of results in terms of expected damage, and 
performance of existing YT fuzes in this application. 
The theory of the Mach effect, the experimental veri¬ 
fication of the theory of oblique reflection, and an 
empirical method for correlating the experimental 
results were also described. 

The direct outcome of the experimental results is 
a set of curves expressing the dependence of peak 
pressure and positive impulse on the height at which 
the charge is detonated, with gauges located at vari¬ 
ous horizontal distances from the charge and at 
various heights above ground. If, from other sources, 
the magnitudes of peak pressure and positive im¬ 
pulse required to produce a specified degree of dam¬ 
age are known the experimental results afford a 
means of establishing the height of burst (the opti¬ 
mum height) required to maximize the damage and 
of predicting the gain in area of damage to be ex¬ 
pected from air burst. 

A blast pressure gauge, which is located at some 
height h g above the ground at a distance d measured 
horizontally from the charge, will record one of two 
general types of pressure-time record, depending upon 
whether the gauge is within, or outside of, the Mach 
region. This is illustrated in Figures 10A and B. 
Figure 10A shows the single-peak type of pressure¬ 
time record obtained when the gauge is flush with 
the ground, or when the triple point T (at which the 
Mach wave and incident and reflected waves meet) 




Figure 10. Pressure-time curves recorded below and 
above triple point. A. Single-peak gauge record. 
B. Double-peak gauge record. 


Lqxfidevtiai^ 














88 


EXPLOSIONS AND EXPLOSIVES IN AIR 


is higher than the gauge. Figure 10B represents a 
double-peak record, such as is obtained when the 
height of the gauge is greater than that of the triple 
point. The incident peak pressure is P 7 , the reflected 
peak pressure P R) and the Mach peak pressure P M . 
The positive impulses in the two cases are propor¬ 
tional to the areas of the crosshatched parts of the 
figures. The times t R and t c are, respectively, the re¬ 
flection time and positive duration of the wave. If the 
gauge is above the triple point, the nearer it ap¬ 
proaches the triple point, the smaller is t R . By plot¬ 
ting the reflection time at a given gauge versus the 
charge height, the charge height at which the triple 
point is just at the gauge can be determined (i.e., 
t R is just zero). Thus the path of the triple point can 
be determined for each charge height, and a family 
of curves, such as those in Weapon Data Sheet 
3A8 155 of Chapter 19 can be obtained. 


the meanings of some of the symbols are as follows. 
Other symbols are defined on the figure itself. 

C explosive charge 
h c height of charge 
I incident shock 

R reflected shock 

M Mach shock (stem) 

S slipstream 
T triple point 
y height of stem 
l — l path of triple point 
^extreme limiting angle for regular reflection 

cl 0 distance on ground corresponding to 

^extreme* 

For simplicity, the stem is shown as a vertical straight 
line, although this is not always the case. Note that 
the definition of a is given a special extension when 
a Mach shock is formed, and that a may be obtuse. 



It was 148 found that, if the path of the triple point 
was expressed in terms of cf> and a — a extrem e (see 
Figure 11), the paths of triple points from all sizes of 
charge, at all heights above the ground, at all distances 
from the charge could be represented by a single 
curve, to a satisfactory approximation. In Figure 11, 


In Figure 12, the dependence of d Q , the horizontal 
limit of regular reflection, on the charge height h c 
is shown, and values of a ex treme are indicated. The 
linear dimensions are normalized by the scaling fac¬ 
tor yK W where W is the weight of charge; d 0 , of 
course, depends upon the pressure-distance function 


C'O^FIDKNTIAT, 



















ANALYSIS OF EXPERIMENTAL WORK 


89 



Figure 12. Theoretical limit for regular reflection 
versus charge height. 


of the explosive charge. With the aid of Figure 12 
together with Figure 13, which shows the dependence 
of (f> on a — ^extreme? the paths of triple points can 
be computed. 

The particularly practical applications of these re¬ 
sults is based upon the experimental fact that the 
pressure at the gauge is maximized when the height 
of charge is 0.9 of that required to cause the triple 
point to pass through the gauge. 

The height of charge which gives the maximum 
positive impulse at a gauge is somewhat greater, in 
general, than that required to make the triple point 
pass through the gauge. However, the optimum 
height is not critical, so that for moderate ranges of 
degrees of damage the same height of burst can be 
used to maximize the damage, whether the criterion 
of damage be peak pressure or positive impulse. 

Figure 14 represents the expected radii of two types 
of damage as functions of the height of burst of a 
4,000-lb LC bomb filled Composition B. These curves 
were estimated from experimental results on the as¬ 
sumption that the mean radius of demolition, maxi¬ 
mum radius of demolition, and mean radius of visible 
damage correspond to impulses of 120, 90, and 55 psi- 
msec, respectively. These impulses would be produced 
midway up a wall 50 ft high, side-on to the blast from 



<r- ^EXTREME IN DEGREES 

Figure 13. versus a . — a extreme. 

the bomb in question at the distances and charge 
heights shown. 

The salient features of Figure 14 are: 

1. The expected radii of damage are increased, on the 
average, about 45 per cent at the maxima so that the 
expected areas of damage would be increased by about 
100 per cent on the average. 

2. The height of burst required to maximize the 
radius of damage is not critical, and is roughly the 
same for both categories of damage considered. A 
height of burst of 30 to 100 ft would produce within 
10 per cent of the maximum obtainable damage; the 
optimum height would be 50 to 60 ft. 

The percentage increase in area of damage is great¬ 
est for the most severe type of damage (demolition). 

That air burst improves the performance (i.e., blast 
damaging power) of a bomb has been demonstrated 
in actual raids, as has already been mentioned. The 
Spezia incidents showed that an air-burst 4,000-lb 
bomb detonating at about 200 ft above the ground 
reduced demolition and doubled the area of visible 
damage compared with previous experience with 
ground-hurst bombs. This is precisely what the ex¬ 
perimental results would predict for a bomb burst so 
high above the ground. The V-l incidents, in which 
the bombs burst above the ground (as a result of strik¬ 
ing trees, etc.) at about the optimum height, add fur¬ 
ther confirmation of the improvement from air burst. 

It has been announced that the atomic bombs used 
over Hiroshima and Nagasaki were burst well above 
the ground. If the atomic bomb were similar to a 
charge of 20,000 tons of TNT as far as blast is con¬ 
cerned and if the peak pressure required to demolish 
a representative Japanese building were 5 psi, the op¬ 
timum height of burst would be about 2,700 ft, and 
the area of demolition would be about 4.9 square 






























































90 


EXPLOSIONS AND EXPLOSIVES IN AIR 



Figure 14. Damage radius from 4,000-lb bomb burst at various heights (estimated). 


miles. Were the same bomb burst at ground level, the 
area of demolition would be about 2.6 square miles 
(using again the assumption that 5 psi is critical for 
demolition). This computation indicates a possible 
90 per cent increase of the effectiveness of an atomic 
bomb by air burst. Weapon Data Sheet 3-A-9 155 of 
Chapter 19 was used for this computation. 

A simple argument which shows that it is physi¬ 
cally reasonable that damage should be increased by 
air burst is as follows: If a bomb is burst very high 
above the ground, so that the reflection from the 
ground occurs much later than does the incident 
shock wave at a gauge also high above the ground, the 
free-air peak pressure exists in the approximately 
spherical shock wave. If the same bomb bursts on the 
ground, only one (hemispherical) wave is produced, 
but the pressure in the wave is the same as that from 
a bomb of twice the weight, burst in free air. (See 
Section 2.2.3.) According to equation (1), the pres¬ 
sure at a fixed distance from a bomb of twice the 
weight would be about 1.5 times that of a bomb of 
equal weight, both being burst in free air. Now sup¬ 
pose the bomb is burst at the optimum height above 
the ground. The shock wave from the image charge 
(O', Figure 2) will add to that from the bomb, and 
will give at least twice, and, for very strong shock 
waves, several times the pressure from the unit 
charge. If it is assumed that the pressure is just 
doubled, the pressure observed near the triple point 
will be 2.0 times that from the unit charge. Hence, 
by raising the bomb from the ground to the optimum 
height, the pressure measured near the ground at a 
fixed distance away is increased by the factor 


2.0/1.5 = 1.3. Since, for strong shocks, the increase 
on reflection may be much more than twice, this esti¬ 
mate is conservative. 

Since the blast intensity is greater in a lateral di¬ 
rection when the bomb is air-burst than when it is 
ground-burst, it is necessary that the intensity meas¬ 
ured above an air-burst bomb be less than that from a 
ground-burst bomb, since the total energy should re¬ 
main constant. This is actually the case, since above 
an air-burst bomb the gauge is high above the triple 
point and the reflected wave does not reinforce the 
incident wave. Hence air burst can be considered as a 
means of introducing asymmetry into the distribution 
of blast intensity around the bomb, in such a way that 
in the lateral direction, where the targets are located, 
the blast is more intense, while in the vertical direc¬ 
tion, where there is no target, the blast is less intense. 

At this point, estimates of the cumulative effect of 
the improvements from filling, case-weight, and air 
burst may be summarized. In Figure 15, the estimated 
relative areas of damage from 4,000-lb bombs of vari¬ 
ous fillings, case thicknesses, and fuzings are repre¬ 
sented as bars whose heights are proportional to esti¬ 
mated relative areas of damage. A thick-cased bomb 
of the GP type (c/w ratio about 53 per cent) filled 
with amatol 50/50 and fuzed instantaneously was the 
standard demolition bomb used by this country at the 
beginning of World War II. A very thin-cased bomb 
fuzed instantaneously filled minol-3 was the latest 
type used by the British. Both the IJ. S. and Great 
Britain were about to introduce proximity fuzing in 
4,000-lb and larger LC bombs when World War II 
ended. 


t V'S I LDHXTIAU 





















































ANALYSIS OF EXPERIMENTAL WORK 


91 


It should be emphasized that this comparison in¬ 
volves only blast bombs. For many purposes, such as 
damaging subsurface water, gas, and electric mains, 
attack of very strong, i.e., blast-resistant structures, 
interdiction of roads, railroads, and bridges, and at- 



Figure 15. Estimated relative areas of blast damage 
from various 4,000-lb bombs. 


tack of troops by fragments, a large blast bomb is un¬ 
suited. 

The proximity fuzing of bombs of the 2,000-lb GP 
type and smaller is not profitable for purposes of in¬ 
creasing the structural damage areas, since the area of 
effectiveness of these bombs, in general, is less than 
the plan area of a target building, and they, therefore, 
function best by penetrating the target and bursting 
within it. However, an entirely different purpose is 
served by bursting fragmentation bombs above the 
ground: it has been shown that for the attack of 
troops in slit trenches, and of aircraft protected by 
revetments, the fragmentation effectiveness is in¬ 
creased by air burst. 

246 Blast in Enclosed Rooms 


ing walls, i.e., until the structure is demolished. 
In addition, the hot gases from the detonation are 
thoroughly mixed with air, and the afterburning 
process is greatly facilitated by the retention of the 
hot gases, at high pressure, by the walls. As a conse¬ 
quence, a pressure-time curve determined by means 
of a gauge placed inside a building is similar to that 
in Figure 16A, which is a reproduction of an actual 
gauge record, obtained as described above. The initial 
shock wave and the reflections may be imagined to be 
superimposed on a “hump.” This hump is due to the 
relatively gradual building up of pressure inside the 
structure as a result of the heat energy released by 
the explosion, both from the original detonation and 
from afterburning. The decay of the shock wave (and 
consequent transformation of its energy into heat) 
can be seen as the damping out of the pressure peaks 
toward the tail of the wave. 

An estimate of the pressure rise in the enclosed 
room which arises from the explosion of a quantity 
of high explosive can be made, using certain simplify¬ 
ing assumptions. 157 If the walls of the room are per¬ 
fectly rigid, nonconductors of heat, without windows 
or other vents, and if all of the available energy of the 
explosive is realized in the initial detonation and sub¬ 
sequent afterburning, the pressure rise A p in psi is 

8 .SH 


where H is the total heat of combustion of the ex¬ 
plosive in kilocalories and V the volume of the room 




a A HIGH EXPLOSIVE 

a (TRITONAL) 


200 

TIME MSEC 


High Explosives 

Thus far, the experimental results that have been 
discussed have had to do with the blast damage effec¬ 
tiveness of the shock wave emitted by a charge deto¬ 
nated in the open, and it was asserted that for such 
application, the large thin-cased bomb with a YT 
fuze is the best type. In this section, the properties 
of bombs burst within a target structure will be con¬ 
sidered. 156 

When a charge is detonated inside a building, the 
initial shock wave is identical with that obtained in 
the open. When this shock wave strikes the walls that 
surround the charge it is reflected and the reflected 
wave bounds back and forth among the walls, floor, 
and roof until its energy has been completely trans¬ 
formed into heat or until there are no longer confin¬ 


UJ 

CL 

3 

if) 

if) 

UJ 

<r 

CL 



B SBX (ALGAS) 


200 

TIME MSEC 


Figure 16. Pressure-time curve recorded for charge 
detonated within building. 


in cubic feet. For a given (large) room, the total posi¬ 
tive impulse I must be proportional to the heat 
evolved: 

I — constant X II . (11) 

Suppose, for example, that a 500-lb bomb bursts 
inside such a building, whose volume is 100,000 cu 
ft. The bomb contains 267 lb of TNT, which has a 
heat of combustion of 3.6 kilocalories per gram; the 


COXFIDKXTI 



































92 


EXPLOSIONS AND EXPLOSIVES IN AIR 


filial pressure rise, computed by means of equation 
(10), is 38.7 psi. Of course, since an actual building 
is far from the type assumed for these purposes, the 
pressure computed can give only a very rough mea¬ 
sure of the true pressure. 

In order to establish the order of merit for explo¬ 
sive fillings for bombs that burst inside target struc¬ 
tures, a series of experiments was performed by SOG 
in collaboration with UERL. 158 Five different ex¬ 
plosives, in the form of bare charges of three charge- 
weights of each explosive were fired in a heavy rein¬ 
forced concrete structure. Piezoelectric gauges were 
used to record the pressure-time curves of the blast. 
Figure IGA is typical of the oscillograms so obtained. 
The positive impulse was computed as a function of 
time of integration, and the results are expressed as 
relative positive impulses versus time. Figure 17 is 
reproduced from a report on relative effectiveness of 
explosives fired in nearly closed rooms. 158 At very small 
times, the relative positive impulses are approximately 
those given in Table 2, Section 2.4.2; i.e., they corre¬ 
spond to those observed in the open. However, at later 
stages in the pressure-time curves, the cumulative 
positive impulses relative to each other change from 
the open air values, and, finally, the order of merit is 
quite different from that in the open. 

Equation (11) predicts that the relative positive 
impulse (measured to very long times) depends line- 



Figure 17. Dependence of relative positive impulse on 
time of integration. 



Figure 18. Dependence of relative total positive impulse 
on relative heat of combustion. 


arly on the energy liberated by the explosion. Figure 
18, in which the relative positive impulses are plotted 
versus the relative heats of combustion (TNT having 
been chosen the standard explosive), shows clearly 
that the simple theon^ is confirmed. The order of 
merit of explosives in enclosed rooms is directly pro¬ 
portional to their heats of combustion. 

In the case of minol-2, the change in relative posi¬ 
tive impulse (with TNT as a standard) from the 
open air value (1.16) to the enclosed room value 
(0.91) is very marked; whereas minol-2 is one of the 
best explosives for open air effectiveness, it is one of 
the poorest for confined blast. Tritonal and HBX, on 
the other hand, are good explosives both in the open 
and inside buildings. In the open, Composition B is 
about midway up the scale of explosives, its positive 
impulse being about 6 per cent better than that of 
TNT; in enclosed rooms, however, Composition B is 
the poorest of the explosives tested. 

The concrete chamber used in the tests described 
above was only slightly vented, with about 1 sq ft 
of opening per 500 cu ft of volume. A more 
usual venting would be about 1 sq ft per 150 cu ft of 
volume. Experiments 156 carried out in a test cham¬ 
ber in which venting could be varied over wide ranges 
showed that the order of the relative positive impulses 
was not very dependent on the degree of venting. 

From model-scale tests of the rupture of brick walls 
resulting from the explosion of a charge within a 
structure, it was 159 concluded that the rupture of the 


Icon FI DENI AL 


















































































ANALYSIS OF EXPERIMENTAL WORK 


93 


walls occur over relatively long periods of time, and 
that the integration of the pressure-time curves in the 
enclosed blast experiments to long times (i.e., over the 
whole positive duration, or nearly so) is justified. 

It is implied by equation (11) that the scaling law 
for enclosed blast should be 

h = (w+y 

h \wj ’ 

where I x and 1 2 are total positive impulses from W 1 
and 1F 2 pounds of explosive respectively and the ex¬ 
ponent m should be equal to unity. In practice, it 
was 108 found that m — 0.9; this further supports the 
conclusion that in enclosed rooms the pressures pro¬ 
duced are directly proportional to the energy released 
and that the heat of combustion of explosives is a 
good measure of their effectiveness under such con¬ 
ditions. The exponent m from open-air blast measure¬ 
ments is about 0.67; in the enclosed-room experi¬ 
ments the transition from the open air to the enclosed- 
room type of scaling occurred at times of the order of 
20 to 40 msec after the beginning of the pressure¬ 
time record. This time is shorter than that observed 159 
to elapse between detonation and rupture in their 
model-scale experiments. 

Slow-Burning Explosives 

It had long been realized that if the energy of com¬ 
plete combustion could somehow be utilized to produce 
blast many combustible substances offered possibil¬ 
ities of greatly improving the blast performance of 
bombs. As was shown in the foregoing part, the blast 
impulse in enclosed rooms is proportional to the heat 
of combustion of the explosive. Such substances as 
paraffin, gasoline, aluminum, etc., have heats of com¬ 
bustion two or three times as great as those of ordi¬ 
nary high explosives. It was proposed that a combus¬ 
tible such as aluminum powder be dispersed and 
ignited in air, and that if the combustion were suffi¬ 
ciently rapid, the resulting blast would be several 
times as energetic as that from a corresponding quan¬ 
tity of high explosive. 

The advantages of a filling for bombs which could 
be dropped from low-flying aircraft and fuzed to burst 
inside a building after a short delay without injury 
to the aircraft from fragments were recognized in 
Britain, and experiments directed to this end were 
performed. 160 

It was found 161 that flake aluminum could be dis¬ 
persed and ignited by a tetryl booster of a few pounds 
weight, and that the resulting burning produced pres¬ 
sures which, if the bombs were inside a building, 



would demolish it. The effectiveness in the open was 
practically nil, owing to the slowness of combustion, 
and consequent lack of a shock wave. Even com¬ 
pared 10 *” 103 to the usual HE fillings (e.g., minol-2) 
in enclosed rooms, these slow-burning explosives 
[SBX] bombs were inferior. However, their principal 
object was accomplished: the fragments were few and 
very short range, so that low-flying aircraft would not 
be endangered. Combustibles other than aluminum, 
such as coal dust and a mixture of aluminum powder 
and gasoline were tried, but without the partial suc¬ 
cess of the early flake-aluminum bombs. 

A hen it was found that the flake aluminum bombs 
would function properly only when the flake aluminum 
was unpolished 164 and that the amount of such 
aluminum available was entirely inadequate, the 
project was dropped by British workers. 

A different point of view was held by some per¬ 
sons in the United States. It was hoped to obtain a 
bomb that would be quite superior to an ordinary 
high-explosive bomb in enclosed rooms by taking ad¬ 
vantage of the high heat of combustion possessed by 
many combustibles. The use of several substances, 
such as paraffin, gasoline, petroleum, aluminum, etc., 
was proposed for this purpose. 165 It was realized that 
the problem lay in dispersing the combustible quickly 
in an adequate volume of air, and igniting it in such 
a way that a very rapid combustion would occur. 

Another proposed use of the SBX principle was in 
sabotage devices: a small burster containing high ex¬ 
plosive could be inserted in bags of flour, etc., and 
cause a dust explosion. Divisions 11 and 19 of the 
NDRC were particularly concerned with this use of 
SBX, and experiments were carried out, at the Mary¬ 
land Research Laboratories, 166 ' 169 using a burster con¬ 
sisting of a small charge of granular TNT and magne¬ 
sium powder encased in an aluminum tube (the 
burster was named Lulu), and, at the Factory Mutual 
Research Corporation, 170 ' 171 using a charge consisting 
of a pressed mixture of sulphur and aluminum powder 
(called Salex) dispersed and ignited by a small charge 
of tetryl. 

A study was undertaken of various combustible 
materials for use as SBX. 156,158,172 Many small-scale 
experiments (with about two pounds of combustible) 
using flake and powdered aluminum, flour, coal dust, 
benzene, 50/50 gasoline/aluminum pow r der, etc., were 
performed. 172 It was concluded that the use of liquid 
hydrocarbons or their mixtures with aluminum pow¬ 
der were suitable for SBX and, with the proper weight 
and kind of burster, were capable of giving blast im- 


iXFIDEXTI 








94 


EXPLOSIONS AND EXPLOSIVES IN AIR 


pulses considerably in excess of those from equal 
volumes of HE charges fired under the same condi¬ 
tions, i.e., in enclosed rooms. The apparently contra¬ 
dictory result that in these experiments the gasoline/ 
aluminum powder mixture was well dispersed and 
ignited and that in the British experiments it was 
not might be explained by the difference in the burst¬ 
ers, which was found to be exceedingly important. 

Further tests 158 on a larger scale (up to about 40 
lb of combustible) confirmed the earlier finding that 
a mixture of aluminum and gasoline (containing 28 
to 38 per cent of gasoline by weight) could be well 
dispersed and ignited by a suitable burster, and that 
the resulting total positive impulse was considerably 
greater than that from an HE charge of the same 
volume. The use of gasoline improves the loading den¬ 
sity of a charge containing aluminum powder and is 
itself one of the best combustibles. 

A typical pressure-time oscillogram from an SBX 
charge (weighing 10 to 11 lb) fired in an enclosed 
room is represented in Figure 16B. The scales of pres¬ 
sure and time are the same for Figures 16A (high-ex¬ 
plosive charge, 13.5 lb of tritonal) and 16B (SBX 
charge, 10 to 11 lb of aluminum/gasoline mixture). 
The differences between the two are clearly discern¬ 
ible: the shock wave from the burster of the SBX 
charge has a very low pressure but, as the combustible 
burns, the pressure builds up to a hump and persists 
at a high level for a long time relative to the positive 
duration of the blast from the high explosive. 

The relative total positive impulses (on an equal- 
volume basis) from SBX, consisting of benzene, and 
of aluminum/gasoline (Algas), are plotted in Figure 
18 versus their relative heats of combustion. The data 
plotted for SBX are from only an intermediate size, 
using about 6.5 lb of benzene or about 10 to 11 lb of 
Algas. Larger charges gave more erratic results, the 
proposed explanation of which had to do with the dis¬ 
proportionately small burster and possibly with the 
presence of water in the structure when they were 
fired. The experimental results for these two SBX 
materials fall remarkably well on the straight line 
that expresses the results from high explosives. This 
indicates that the combustion of the SBX was ad¬ 
vanced toward the same degree of completion as was 
that of the HE charges. 

The improvement obtainable from the Algas over 
that from the best of the high explosives can be ex¬ 
pressed in terms of the sizes of buildings which bombs 
filled with each could presumably demolish : the Algas 
bomb should demolish a building of 55 per cent larger 


volume than that which the tritonal bomb could de¬ 
molish. 

Although SBX requires further study to make cer¬ 
tain that it is advantageous from a military point of 
view, the small-scale results show great promise and 
suggest future lines of experimentation. 

From observations of the effect of bombs on targets, 
the AX-23 Group 75 concluded that the effectiveness 
of a 500-lb GP bomb in a direct hit is about 10 times 
that from a near-miss. This ratio decreases as the 
bomb size increases, and large blast bombs whose 
effective damage area is greater than that of a given 
target structure, are less effective in direct hits than 
in near-misses. With such bombs, a direct hit demol¬ 
ishes the target structure, but the walls of the building 
struck shield adjacent buildings from the blast, ab¬ 
sorbing the energy in the blast. For 500- and 1,000-lb 
GP bombs, it is, therefore, more important to increase 
their direct-hit effectiveness rather than their near- 
miss effectiveness. The use of SBX may well offer this 
advantage: its improved performance in a direct hit 
may more than compensate for its lack of near-miss 
effectiveness (for SBX is practically without effect 
in the open). 

A compromise filling for small (500- or 1,000-lb) 
GP bombs is suggested by the applicability of equa¬ 
tion (11) which has been experimentally verified: a 
conventional high explosive having an increased alu¬ 
minum content (such as TXT/A1, 60/40, or even 
40/60) should be markedly superior to tritonal in 
enclosed rooms and not much less effective in the open. 
Thus the same bomb might be practically as good for 
cratering, earth shock, etc., and very much better for 
demolition by a direct hit. Mixtures such as TXT/A1, 
60/40, have been tested in bombs in the open 98 and 
were found to give blast impulses about equal to those 
from tritonal. The total blast impulse from TXT/A1, 
60/40, should be about 20 per cent greater than that 
from an equal volume of tritonal, both being measured 
in enclosed rooms. The corresponding increase for 
TXT/A1, 40/60, would be about 50 per cent. 

An additional advantage to the SBX type of filling 
lies in its presumably greater incendiary effect. Flame 
temperatures remain very high for longer periods 
from SBX than from conventional HE. 

2 4 7 The Variation of Peak Pressure 
and Positive Impulse with Distance 

Theory from the Char S e 

In the study of explosions and the shock waves 
resulting from them, one of the most important and, 










ANALYSIS OF EXPERIMENTAL WORK 


95 


at the same time, one of the most difficult problems 
was to obtain the laws that govern the propagation of 
the shock waves through the air. The need for a theo¬ 
retical solution to this problem was acute, both be¬ 
cause no fundamental understanding of explosion 
phenomena was possible without it, and because the 
experimental difficulties in measuring the pressure in 
a shock wave close to a charge were great, and the 
experiments liable to serious error. On the other hand, 
the theoretical difficulties were also great and, at best, 
simplifying assumptions had to be made. 

By applying the equations of hydrodynamics, with 
additional simplifying assumptions, an approximate 
solution was obtained 173,174 for the propagation of 
blast waves in air. The straightforward numerical 
integration of the equations of hydrodynamics is ex¬ 
ceedingly laborious and was, therefore, applied only 
to a limited extent. 175 ' 177 In all these procedures, the 
problem was simplified by assumptions and the exact 
Hugoniot curve for air was not used. As a result of 
the limitations imposed by the approximations, an ac¬ 
curate numerical solution for the propagation equa¬ 
tions, from the surface of the charge outward to any 
desired distance from it, could not be obtained. 
Asymptotic solutions were obtained for the propaga¬ 
tion at low pressures, where the assumption could be 
made that the entropy change across the shock front 
could be neglected. Other assumptions led to solutions 
valid for regions close to the charge. 

More recently, a new theory was devised 178 ' 183 which 
involves an assumption concerning the shape of the 
energy-time curve, which amounts to assuming that 
the pressure-time curve for the blast wave at large dis¬ 
tances is linear (during the positive phase). The 
theory allows use of the exact Hugoniot curve for 
air 117 and makes it possible to compute the peak pres¬ 
sure, positive impulse, and energy of the shock wave 
as a function of distance from the charge, over any 
desired range of distance. 

In its first form, the theory required two experi¬ 
mentally measured quantities, such as the pressures 
at two distances, the pressure and impulse at one dis¬ 
tance, etc., in order to evaluate two constants of inte¬ 
gration of the theory. Later, the necessity of using 
experimental values was eliminated 183 by considering 
the thermodynamic properties of the explosive and of 
the detonation products. Two alternative assumptions 
concerning the detonation state were presented. In 
one, the “instantaneous” detonation state, the explo¬ 
sive was imagined to be converted into its products at 
high temperature and pressure, contained in its orig¬ 


inal volume. In the second, the Chapman-Jouguet 
conditions were assumed to apply. Of the two hypo¬ 
thetical states, experimental evidence favors the Chap¬ 
man-Jouguet detonation state. 

Experimental Results — Free-Air 
Pressures and Impulses 

The theoretical work applies only to the detonation 
of a charge in free air, i.e., with charge and gauges 
well removed from reflecting surfaces such as the 
ground. Unfortunately, relatively few studies of the 
variation of peak pressure with distance in free air 
have been made. Moreover, until quite recently,. the 
effects of the flow of air past the gauge on the recorded 
pressure were not recognized, so that the absolute val¬ 
ues of pressure from much of the earlier experimental 
work are in doubt, particularly at higher pressures. 

Recent experimental determinations of peak pres- 



Figure 19. Logarithmic plot of free air pressure versus 
distance curve for cast TNT. 


L0.YFIDKXTI.YLj 
































96 


EXPLOSIONS AND EXPLOSIVES IN AIR 


sures as functions of distance from the charge in free 
air are those of UERL, 87 * 89,90 Princeton University 
Station, 184 ARD, 153 and SOG. 91 The charges used by 
UERL were cylindrical cast TINT (3.5 to 41.7 lb), 
those by ARD were cylindrical cast Composition B 
(67 lb), those by SOG were cylindrical cast TNT 
(11 lb), and those by Princeton University Station 
were rectangular blocks of pressed TNT (0.5 lb). The 
agreement among UERL, ARD, and SOG results is 
excellent (after taking into account the differences 
due to the use of Composition B by ARD). Moreover, 
these results fit the theoretical curve 183 within experi¬ 
mental error. The curve obtained by Princeton Uni¬ 
versity Station, however, is different from the others, 
being steeper and crossing the theoretical curve. There 
is good reason to believe that the Princeton University 
Station curve is not in error, but that a real difference 
exists because of the shape of the charges. Since the 
cylindrical charge shape is more symmetrical, and 
less likely to give special results, it is not surprising 
that experiments using them are in better agreement 
with theory. Figure 19 is a logarithmic plot of the 
free-air pressure versus distance curve for cast TNT, 
with the scale of distances normalized by dividing by 
the cube root of the charge-weight. 

Available data on the dependence of positive im¬ 
pulse on distance in free air are even fewer than for 
peak pressures. Only the data of UERL 87,90 and 
SOG 91 are available for this purpose. The data from 
UERL are internally consistent and lie 6 per cent 
below the theoretical curve, on the average. The SOG 



Figure 20. Logarithmic plot of positive impulse versus 
distance in free air for cast TNT charges. 

data lie, on the average, 14 per cent above the theo¬ 
retical curve. Thus, it is again true that the theory 
is in agreement with experimental determinations of 
positive impulses, within the uncertainty of the latter. 
Figure 20 is a plot of the positive impulse versus dis¬ 
tance in free air for cast TNT charges, with both 
quantities divided by the cube root of the weight of 
the charge. 



Figure 21. Theoretical positive impulses versus distance, cast TNT in free air. 


























































PEAK PRESSURE IN PSI 


ANALYSIS OF EXPERIMENTAL WORK 


97 



Figure 22. Pressure-distance curves, experimental ( 


) and theoretical (-). 





















































































PEAK PRESSURE IN PSI 


98 


EXPLOSIONS AND EXPLOSIVES IN AIR 



Figure 23. Pressure-distance curve (experimental and theoretical) for ground-burst blast of bare charges. 

































































ANALYSIS OF EXPERIMENTAL WORK 


99 


The theory predicts a very interesting behavior of 
the positive impulse at small distances from the 
charge: as the distance from the charge is increased, 
beginning at its surface, the positive impulses first 
rise and reach a maximum, then decrease. Figure 21 
is a plot of the theoretical positive impulse versus dis¬ 
tance curve for spherical charges of cast TNT on a 


at the greater distances on both piezoelectric gauge 
measurements and velocity measurements. The smooth 
curve of Figure 22 represents these data; no compar¬ 
ison with theory is available, since the new theory 183 
has not been applied, numerically, to pentolite. On the 
same graph, however, the theoretical pressure-distance 
curve for cast TNT is plotted for comparison. 



Figure 24. Experimental positive impulses versus distance curves (on ground) from various sources. 


smaller scale than that of Figure 20 and with a greater 
range of distance. The existence of the maximum, 
which occurs at about 1 ft from a charge weighing 
1 lb, has never been confirmed by experiment, since 
pressures at this distance are in excess of 1,000 psi. 

Measurements of peak pressure, very close to the 
charge, 185 at intermediate distances, 186 and in the 
range 90 covered by Figure 19, using in all cases spher¬ 
ical charges of pentolite, centrally initiated, have been 
made. Those close to the charge are based on shock- 
velocity measurements (see Section 2.3.3) and those 


Experimental Results — Ground-Level 
Pressures and Impulses 

As described in Section 2.4.5, a charge detonating 
on the ground produces a blast wave having the pres¬ 
sures and impulses that a charge of twice the weight 
would give in free air, providing there were no crater, 
and providing the ground were a perfect reflector of 
the shock wave. In practice, of course, craters are 
formed, and the ground absorbs energy from the 
shock wave as it proceeds. Moreover, differences in 
soil can cause different degrees of energy absorption. 


lOXFIDENTIAL*, 
























































100 


EXPLOSIONS AND EXPLOSIVES IN AIR 


As a result, rather more scatter in results can be 
expected and is found when the charges are resting 
on the ground than when they are detonated in free 
air. As a result of such uncertainties, the free-air 
theory can serve only as a theoretical upper limit to 
the blast intensity for ground-burst charges. 

Experimental measurements of ground-burst blast 
pressures and impulses are available from several 
sources. In order to obtain a representative sample of 
these measurements, some results from British Labo¬ 
ratories (BEL and AED), UEEL, Princeton Univer¬ 
sity Station, and BEL have been compiled, averaged, 
and plotted in Figures 23 and 24. A large range of 
soil conditions, climate, charge sizes, and a narrow 
range of gauge heights are involved. All BEL meas¬ 
urements were made with the bomb supported a short 
distance off the ground, and a correction for this was 
necessary. For measurements where bombs or other 
cased charges were used, the results have been ad¬ 
justed so that all plotted values refer to bare charges. 
Differences in explosives were also taken into account 
by use of the data of Section 2.4.2. 

In Figure 23, the highest curve (pressure versus 
distance) is that from BEL results 105 on bombs of 
all sizes, charge-weight ratios, etc., adjusted by use 
of a function such as that of Figure 5 for the effect 
of the bomb case. The next higher curve is that from 
bare charges of Composition B, varying from 8 to 
550 lb but mostly about 67 lb. 104,106,187 ' 189 Data 
from EEL and AED were averaged for this curve. 
The effect of the difference in blast between TNT 
and Composition B was taken into account. The curve 
for 10-lb bare charges of TNT, determined both by 
means of piezoelectric gauges and the shock-wave 
velocity technique 190 is almost indistinguishable from 
the British bare-charge results. The theoretically pre¬ 
dicted curve is also plotted. This curve was obtained 
by taking the free-air pressures for a doubled charge- 
weight and should represent an upper limit, since the 
ground is not a perfectly rigid reflector. Although the 
evidence from the difference between the curves from 
large charges and small is by no means convincing 
that the principle of similitude does not hold exactly, 
the direction in which deviations from exact scaling 
occur is the one which fits the reasoning of Sec¬ 
tion 2.4.3. 

In Figure 24 (positive impulses versus distance) 
the curve on which Weapon Data Sheet 3A2* 97 of 
Chapter 19 is based is considered the most generally 
applicable one for moderately large charges. This 
curve was obtained principally from many British 


measurements of the blast from bombs of all sizes, 
the effects of the case being taken into account. The 
next lower curve is that from a large number of 
British measurements of the blast from bare charges 
of Composition j$ > i°4,io6,i 8H89 qq ie curve from 

UEEL measurements of the blast from 10-lb charges 
of TNT 190 is very close to the British bare-charge 
curve. The BEL results 105 from bombs and large bare 
charges are somewhat higher than those represented 
by Weapon Data Sheet 3A2*. The Princeton measure¬ 
ments in which VUlb rectangular blocks of TNT were 
used 141 are very close to the British and UEEL bare- 
charge results, but the latter curves are not so steep. 
Effects that are due to the special charge shape may 
be involved. A theoretical curve, based on the free-air 
curve from theory but using doubled charge-weight, 
is also given. A striking difference between this curve 
and the experimental ones is that the latter are 
straight lines, whereas the theoretical curve is concave 
downward. Presumably, the special reflection and ab¬ 
sorption effects of the ground are responsible for this 
difference. In Figure 24, as in Figure 23, the curves 
seem to be progressively higher, the larger the weight 
of charge. 

An interesting feature of these curves is the lower 
rate of decay with distance of both pressure and im¬ 
pulse for bare charges as compared with bombs and 
the greater rate of decay for ground-burst charges 
than for free-air charges (compare Figures 19 and 
20). For comparison, the curves obtained by using the 
free-air results for charges of doubled weight (to take 
into account ground reflection) are also plotted in 
Figures 23 and 24. 


2 . 4.8 


Theory 


The Air Blast from Line Charges; 
Mine Field Clearance 


The basic principles of the theory 181 of propagation 
of shock waves from explosive sources in air and 
water have been applied to a line charge, i.e., to a 
charge one of whose dimensions is much greater than 
the other two. This theory 191 takes into account the 


finite detonation velocity of the explosive and is ap¬ 
plicable to an infinitely long cylindrical stick, initi¬ 
ated at one end. By assuming the detonation veloc¬ 
ity infinitely great, a simplified set of equations is 
obtained which is applicable at rather large distances 
from the charge. The theoretically predicted pressure 
and impulse versus distance curves for an infinitely 
long cylindrical charge of cast TNT detonated in free 
air are given in Figures 25 and 26. The scales of im- 








ANALYSIS OF EXPERIMENTAL WORK 


101 



DISTANCE d/W 1/2 IN FT/LB j/ 2 


Figure 25. Theoretical dependence of peak pressure on 
distance from line charge of cast TNT. 

pulse and distance are normalized by dividing each 
by y/W, where W is the charge-weight per foot; the 
square root rather than the cube root is the scaling 
factor for line charges. 

The general shapes of the pressure and impulse 
versus distance curves for line charges are very sim¬ 
ilar to those for point charges (compare Figures 21, 
22). The principal difference is that, for line charges, 
the rate of decrease of peak pressure and positive im¬ 


pulse with distance is less than for point charges. 
There is a predicted maximum in the positive impulse 
versus distance curve for line charges, as well as for 
point charges. The existence of this maximum has not 
been demonstrated experimentally for, as is the case 
with point charges, measurements of positive impulse 
so close to the charge are very difficult. In both cases, 
the maximum is predicted to occur at a distance from 
the charge where the peak pressure is of the order of 
1,000 psi. The possible existence of this maximum 
may have a great practical importance in clearing 
mine fields by use of explosives. (See part 2 below.) 

Clearance of Mine Fields by Explosives 

Land mines constitute one of the most effective de¬ 
fensive weapons; their use in very large numbers 
often practically immobilized the mechanized units of 
advancing armies and exacted a large toll of killed 
and injured troops and crippled vehicles. One of the 
most acute problems in ordnance was the development 
of means of detecting, removing, and exploding land 
mines sown by the enemy. To do this, many devices 
were employed, none with complete success. Among 
other methods of mine field clearance, an impor¬ 
tant one used explosives; the blast from explosive 
charges was capable of causing the fuzes of some 
types of mines to function. For physical properties 
of line charges, see Weapon Data Sheet lA7b of 
Chapter 19. 155 

Two general types of mines were used. (1) Anti¬ 
tank mines were so devised that the pressure of a 




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CO 









































































j u 











































Q_ ™ 

- 20 

3 15 

\ 

*—< i n 













































































































1 u 

$ 8 
d 1 

CL D 

A 

























































































































































































































Ld 3 
> 

H - 2 
CO 

O |.5 
CL 
































































































' 


















































.d)4 .06.08.1 J5 J 2 .3 .4.5.6 .8 I 1.5 2 3 4 5 6 8 10 15 20 30 40 6080 100 

DISTANCE d/W 1/2 IN FT/LB ' /2 


Figure 26. Theoretical dependence of positive impulse on distance from line charge of cast TNT. 


confidential’ 

























































































































































































































102 


EXPLOSIONS AND EXPLOSIVES IN AIR 


heavy vehicle such as a tank would explode the mine, 
but the weight of a man was insufficient. (2) Anti¬ 
personnel mines were fitted with trip wires, triggers, 
etc., which would cause the fuze to function even if 
they were only slightly disturbed. Both types of mines 
were usually used in the same field; the antitank 
mines made the passage through the field hazardous 
for armored vehicles, and the antipersonnel mines were 
equally hazardous for the sappers who entered the field 
in advance of tanks to detect and dearm the mines. 
In addition, the field was usually under enemy fire. 

Explosives in the form of bombs, and other special 
point charges, line charges, and “plane” charges were 
used or tested. Aerial bombing of mine fields, using 
navy depth bombs and 500-lb GP bombs, was tested, 192 
and static trials of bombs suspended at various heights 
above a mine field to simulate air-burst bombs were 
carried out. Alternate explosive fillings (TNT and 
tritonal) were evaluated for mine field clearance. 194 
It was found that air-burst bombs cleared mines 
to a greater distance than did ground-burst bombs, 
and that bombs filled with tritonal were more effec¬ 
tive than those filled with TNT. (Similar tests, using 
rocket heads filled TNT and torpex-2 195 showed that 
torpex was markedly superior to TNT.) On the whole, 
however, aerial bombing of mine fields was considered 
an ineffective method, largely owing to the scatter in 
the points of burst, which necessitated a very heavy 
bombing to insure that a continuous path would be 
cleared. Even under the conditions of the test, when 
the target mine field was well marked, many bombs 
missed it entirely. 

For use in clearance of mine fields, line charges of 
several types were developed by the U. S. Army Engi¬ 
neer Board, at Fort Pierce, Florida, and the A. P. 
Hill Military Reservation, Virginia. Antipersonnel 
mine-clearing devices were line charges of low weight 
of explosive per foot, intended to be launched by a 
variety of means over a mine field, and detonated. 
Some of these devices were: (1) detonating cord cable 
kit, Ml, 196 consisting of a coil of flexible explosive 
“rope” composed of 13 (and later 19) strands of 
Primacord detonating fuze; (2) infantry snake, mine- 
clearing antipersonnel Ml, 197 consisting of an assem¬ 
bly of corrugated magnesium-alloy channels bolted 
together and filled with two rows of paper-wrapped 
explosive charges; and (3) a flexible hose 193,198 ' 204 
(the infantry hose), 1 in. in diameter, which could be 
laid across the mine field and filled, in situ , with a 
liquid explosive. The detonating cord was launched 
through the air by means of a rocket; the infantry 


snake skidded along the ground, propelled by a rocket 
mounted in its nose; and the flexible hose was to be 
paid out by a rapidly rolling wheel or by a rocket 
launched from an armored vehicle toward the mine 
field. 

For clearance of antitank mines, much heavier ex¬ 
plosive charges must be used than for antipersonnel 
mines, both because of the relative insensitivity of the 
former to blast, and because a wide lane is required 
for large vehicles. Some of the line charges developed 
for clearing antitank mines were : (1) snake, M2A1, 205 
and M3 206 consisting of overlapping corrugated steel 
or aluminum plates holted together to form two 
parallel troughs in which special cartridges of explo¬ 
sive were placed; (2) a flexible hose 207 (the dragon 
or tank hose) similar to the infantry hose but of 3-in. 
diameter; and (3) the projected line charge [PLC] 
consisting of a cloth tube containing plastic explosive 
(Composition C3) provided with an axial nylon rope 
and constricted at short intervals by tying with twine. 
The snakes were assembled in the rear and then towed 
to the edge of the mine field, whence they were pushed 
by a tank into the field, and then detonated. The tank 
hose was to be launched by projection from a rocket 
tube mounted on a tank. The PLC was to be tied to a 
rocket (the coiled charge and rocket being towed by a 
tank to the edge of the mine field) and launched 
through the air. 

For clearance of S mines, which were very blast re¬ 
sistant, a plane charge, consisting of a mat of woven 
Primacord, was developed. 193,198 ' 204 This charge (the 
carpet-roll torpedo) was to be launched by rockets 
propelling the roll across the mine field and unrolling 
as it went. 

All of the weapons described were capable of clear¬ 
ing mines, but each had its disadvantages. The chief 
difficulty was that a charge that was capable of clear¬ 
ing an adequate path was heavy and cumbersome, and 
in the process of laying the charge, personnel were 
exposed to enemy fire. Detonation of a large charge 
near a tank endangers the tank and occupants. How¬ 
ever, the blast effect inside the tank is not normally 
hazardous to personnel. 208 

In order to test mine field clearing devices, mines 
simulating certain enemy types in all possible respects 
were developed and produced in quantity. These 
dummy mines were filled with inert material, and the 
fuze was so arranged that it could be determined, after 
the test, whether or not an actual mine fuze would 
have functioned. The universal indicator mine 209,210 
was developed by the Gulf Research and Develop- 


Voxftdexttat; 





ANALYSIS OF EXPERIMENTAL WORK 


103 


ment Company, Division 17, NDRC, to serve, as its 
name implies, as a mine that could be calibrated 
against any type of actual mine. The results of tests 
using the universal indicator mine could be used to 
predict the clearance of most types of mines with 
which it had been compared. Mine fields consisting of 
these and other indicator mines were laid out in the 
way best calculated to yield results of statistical valid¬ 
ity, and the explosive charge being tested was deto¬ 
nated among them. The mines were then uncovered 
and their fuzes examined. 

Experimental data on the clearance of many types 
of mines by various types of explosive charges are con¬ 
tained in the reports of the U. S. Army Engineer 
Board; 192,193,198 ' 204 these data have been analyzed 
statistically and reported by the Statistical Research 
Group, Princeton University. 211 It is clear from these 
data that type of soil, time since burial, depth of 
burial, and moisture in the soil are all important fac¬ 
tors in determining the distance from the charge at 
which a mine may be detonated 


</> 

CL 

2 

Ui 

<r 

'D 

to 
Ui 

cr 
cl 

X 
< 

IfcJ 
Q. 

I 


8 
6 

3 4 5 6 8 10 15 20 30 40 50 60 80 CO 150 

DISTANCE IN FT 

Figure 27. Peak pressure versus distance for various 
line charges. 

Although it was known from experiment that the 
blast from line charges was capable of detonating 
mines, there was at first no way other than trial and 
error to predict the performance of new types of 
charges, or of old types with new explosive fillings. 
Two things were needed: first, an applicable theory of 
the functioning of mines, relating the physical prop¬ 
erties of the fuzes to the parameters describing the in¬ 
tensity of the blast, and second, measurements of the 
peak pressure and positive impulse in the blast from 
various line charges. 




by blast. 


A simple theory of the response of simulated Teller- 
mine 43 [TMi-43] to blast was developed; 212 this was 
later applied to the response of the universal indicator 
mine. 213,214 These theories require a knowledge of 
the pressure-distance and impulse-distance curves for 
each explosive charge to which the theory is to be ap¬ 
plied. 



Figure 28. Positive impulse versus distance for various 
line charges. 


In Great Britain investigations of the functioning 
of German mines and simulated mines, theoretical 
studies of their response to blast loading, 215 develop¬ 
ment of line charges, and measurement of the blast 
intensities from line charges 218,219 have been carried 
out. 

If mines are more deeply buried than 2 in. be¬ 
low the surface of the ground, it is found that, in a 
narrow belt just beyond the crater from the explosive 
charge, a large fraction of the mines are not detonated, 
and, indeed, many mines are rendered more sensitive 
and, therefore, hazardous. Beyond this region it is 
found that essentially all mines are cleared for a cer¬ 
tain distance; at still greater distances, the fraction 
of mines detonated falls off rapidly. This phenomenon 
(of low expectation of detonation near the crater) 
is called the “skip effect” or “probability dip.” It con¬ 
stitutes a serious disadvantage of the explosive method 
of clearing mine fields, since it is precisely in and ad¬ 
jacent to the crater that tanks must travel. Many hy¬ 
potheses have been advanced to account for the skip 
effect, but none has been verified by experiment. It 
may be that the existence of a maximum in the im¬ 
pulse versus distance curve (Figure 26) is somehow 


CONFIDENTIAL 














































































































































104 


EXPLOSIONS AND EXPLOSIVES IN AIR 



DISTANCE d/W^ FT /LB / 2 

Figure 29. Peak pressure versus distance for line charges. 


responsible for the effect. Another hypothesis is that 
earth-borne shock is responsible; the skip effect is 
not observed with air-burst point charges. 

Experimental Peak Pressure and Positive 
Impulse versus Distance Curves 

Blast pressures and positive impulses were meas¬ 
ured along the perpendicular bisectors of several of 


the line charges mentioned above. 190 In Figures 27 
and 28 these results are plotted as functions of dis¬ 
tance from the charge. In Figures 29 and 30 the same 
results are represented on a reduced scale by dividing 
the distances and positive impulses by the square root 
of the charge-weight per foot, in each case. The ratios 
of lengths of charge L (ft) to square root of weights 








































































ANALYSIS OF EXPERIMENTAL WORK 


105 



Figure 30. Positive impulses versus distance for line charges. 


per foot, W* (lb per ft) 5 are indicated for each 
charge. In Table 5 the data on the physical properties 
of the line charges used are listed. 

British measurements 218,219 have shown that, over 
a great part of the length of the line charge, the pres¬ 
sures and impulses measured along lines perpendicular 


Table 5. Dimensions and weights of line charges.* 


Charge 

Explosive 

Wt exp. 

per foot Length Case 

(lb/ft) (ft) material 

Case wt 
per foot 
(lb/ft) 

Detonating PETNf 

0.078 

30 

Fabric 

0.032 

cord 






Infantry 

TNT/NG 981/H 

0.64 

100 

Magnesium 

snake 




alloy 

0.54 

Infantry 






hose 






(1-in. hose) EL389BJ 

0.47 

50 

Impregnated 

Tank hose 




Fiberglas 

0.040 

(3-in. hose) EL389B + 

4.5 

154 

Impregnated 





Fiberglas 

0.15 

M3 snake 

Amatol 80/20 

14.4 

320 

Aluminum 9.4 


*The lengths of charge, weights, etc., are those used in blast measure¬ 
ment tests. 190 In actual weapons, other lengths may be used, as well 
as inert sections which do not contribute to the blast. 


tThirteen strands of Primacord detonating fuse contained in a woven, 
impregnated outer jacket. Pentolite 50/50 is more commonly used as an 
explosive filling for the detonating cord. 

fEL389B has the composition: nitroglycerin (NG) 00.0%, DNT oil 
27.6%, TNT 11.8%, stabilizer 0.6%. 


to the charge are independent of the position along 
the charge. Near the ends of the charge, however, this 
is not true. 

The application of the square root scaling principle 
to the 1- and 3-in. liquid-filled hose was found to be 
roughly applicable. Since the charges were not infi¬ 
nitely long, it was necessary also to scale the lengths 
of the charges in the same way, i.e., to keep L/W- 
fixed. That the blast pressures and impulses from 
charges of all types do not fall on the same curves 
when the impulses and distances are reduced by the 
square root of the charge-weight per foot (see Figures 
29, 30) is due to a combination of the effects of differ¬ 
ent values of L/W h , different charge-weight ratios, 
different explosive fillings, and different cross-sectional 
shapes of charge. Experiments show that, for pressures 
measured opposite the center of the charge, L/W 1 is 
essentially “infinite” if it is greater than about 80 

ftVlb*. 

A remarkable feature of the impulse versus distance 
curves is the inflection in slope. There is a range of 
distance from the charge over which the impulse 
changes very little; this is predicted by the theory. 191 
No quantitative comparison with the theoretical pre¬ 
diction can be made because of unknown effects of the 
differences in filling, case, and shape, and because the 


CONFIDENTIAL 












































106 


EXPLOSIONS AND EXPLOSIVES IN AIR 


theory applies to detonation in free air, whereas all 
of the line charges were fired on the ground. An ap¬ 
proximate estimate of the ground-level values for 
TNT from the theoretical results for free air can be 
obtained by computing the pressures and impulses 
from twice the weight of charge. 

There are several methods by which the effective¬ 
ness of the line-charge weapons can be increased. Al¬ 
most any explosive gives greater blast than amatol 
80/20. For example, aluminized explosives might in¬ 
crease the width of cleared path by about 30 per cent 
or possibly more. The skip effect might also be re¬ 
duced with superior explosives. The case-weight 
should obviously be held to a minimum; the M2A1 
snake, made with steel plates, is less effective than is 
the M3 snake, which is made with aluminum; the 
latter has a total weight 3,000 lb less. Utilizing air 
burst, if it were feasible, would also increase the effec¬ 
tiveness of line charges, as has been shown by experi¬ 
ment. 220 

The theory 212 " 214 can be applied to predict the 
clearance of certain mines calibrated against the uni¬ 
versal indicator mine, as well as to the TMi-43 indi¬ 
cator mine. In Table 6 a few predictions so calculated 
are compared with experimental results. Although the 
theory gives good agreement with experiment for point 
charges, it predicts too wide a cleared path for line 
charges; the fault may lie with one of the simplifica¬ 
tions of the theory, namely, that the pressure-time 
curve can be considered linear. Experiment 190 shows 
that, in the region of interest, the pressure-time curves 
are more nearly exponential than linear. 

The use of line charges, such as sections of M3 
snakes, has been proposed as a demolition device to be 
used against defended towns: it was suggested that 
charges could be pushed into streets by tanks and de¬ 
tonated after withdrawing the tanks. Computations 
of the expected areas of damage from these devices 
using the impulse criterion for blast damage indicate 
that the line charge, so used, would have a higher 
MAE per ton, than would ordinary bombs using the 
same filling. This, however, is not ordinarily an eco¬ 
nomical method of delivering explosive. 

2 . 4.9 The Eff ec t of Atmospheric Pressure 
on Peak Pressures and Positive Impulses 

Almost all measurements of blast pressures have 
been made at elevations not far above sea level. Some 
uses for explosives, however, might involve the deto¬ 
nation of charges far from sea level, and consequently 


Table 6. Comparison of clearance of indicator mines 
with that predicted by theory. 


A. Point charges 213 TMi-43 indicator mine. 

Distance for 

Charge Depth of burial (in.) 30% clearance (ft) 




Observed 

Computed 

AN-M47A-2 

2 

21 

24 

(89-lb TNT) 

4 

19.5 

19 


6 

14 

17 

Bare TNT, 8-lb 

4 

3.7 

4.5 

Bare TNT, 64-lb 

4 

17 

18.5 

B. Line charges 214 Universal indicator mine 



Distance for 

mine reading 

Wt of charge 

Depth of burial 

equal to 0.080 in. (ft) 

(lb/ft) 

(in.) 

Observed 

Computed 

4.5 

2 

28 

37 


4 

23 

32 


6 

20 

26 

10 

2 

28 

62 


4 

25 

56 


6 

22 

53 

15 

2 

39-53 

78 


4 

36-45 

74 


6 

28-37 

69 


at low atmospheric pressures. That both temperature 
and pressure affect the propagation of blast waves is 
known from dimensional arguments. Expressions 
have been obtained for such effects. 221 

The theory of propagation 181 of shock waves from 
explosive sources in air and water has been applied to 
the propagation of blast waves in regions where at¬ 
mospheric pressure and temperature were different 
from those at sea level. 222 It was assumed that the 
energy delivered by the explosion to the atmosphere 
was the same at all altitudes. It is predicted that both 
peak pressure and positive impulse are less the 
greater the altitude; the change of shapes of the pres¬ 
sure-distance and impulse-distance curves were com¬ 
puted. 

The blast measurement groups of the SOG at Tulsa, 
Oklahoma, measured the blast from charges fired at 
three elevations above sea level: 650, 6,600, and 14,100 
ft, in order to determine the effect of atmospheric 
pressure on the pressures and impulses from three 
kinds of explosives; tritonal, TNT, and blasting gel¬ 
atin were used. 91 Blast measurements were made at 
four distances from the charge in free air. Within the 
experimental error, it was found that the effects of 
changes in atmospheric pressure on peak pressure and 
positive impulse are independent of distance from the 
charge and nature of the explosive, and that the re¬ 
sults are not significantly different from theoretical 
prediction. 
















ANALYSIS OF EXPERIMENTAL WORK 


107 


The effects of the atmospheric pressure on the blast, 
expressed as the average peak pressures and positive 
impulses relative to those near sea level are given in 
Table 7. The theoretical predictions for cast TNT are 
also included for comparison. 

Although the experiments showed no significant 
differences in the effect of altitude on pressures and 
impulses depending upon the nature of the explosive 
or gauge-to-charge distance, the theory predicts that 
over a very wide range of distance (much wider than 
that in the experiments) the effects depend upon both 
the kind of explosive and the distance from the charge. 


Table 7. Effect of atmospheric pressure on peak 
pressure and positive impulse.* 


Altitude 

6,600 ft. 

14,100 ft. 

Average atmos¬ 
pheric pressure 
(in. of mercury) 

24.43 

18.04 

Average tem¬ 
perature (F) 

76 


38 



P2/P1 

I2/I1 

P3/P1 

I3/I1 

Experimental 91 

0.93 ±.026 

0.97 ±.039 

0.87 ±.038 

0.87±.027 

Theoretical 222 

0.90 

0.93 

0.82 

0.87 


* Subscripts refer to elevation (ft) above sea level: 1 = 650 ft, 2 = 6,600 ft, 
3 = 14,100 ft. 


2.4.10 Miscellaneous Experimental Results 

The Effect of Charge Shape ox the Blast 

Most explosive charges of military importance are 
not spherical in shape, and for some applications, it 
is important to know the blast intensities in all direc¬ 
tions from the charge. Unfortunately, very few studies 
have been made of the blast pressures in various di¬ 
rections around charges; comparisons of explosives, 
for example, have usually been based upon measure¬ 
ments along lines perpendicular to the axis of the 
charge, i.e., approximately in the plane of its equator. 

In one series of trials, the ARD 223 measured the 
blast in various directions around 500-lb MC bombs 
which were supported with their axes horizontal a few 
feet from the ground. It was concluded that over the 
range of measurement (which was from 30 to 80 ft 
from the bomb) the pressure and impulse versus dis¬ 
tance curves were not significantly different in differ¬ 
ent directions. 

That the blast pressures (and impulses) are not 
equal for all orientations around the charges for some 
charge shapes, was demonstrated for rectangular 
blocks of TNT, 224 and for cylindrical charges of vari¬ 
ous explosives 92 in which two proportions of cylindri¬ 


cal height to diameter were used. These measurements 
were made at distances roughly corresponding to those 
in the bomb trials mentioned above (i.e., after allow¬ 
ing for the difference in weights). Although the effects 
varied considerably, depending on the explosive used, 
in general it was found that the blast pressures and 
impulses measured opposite the base of the charge 
were greater than those opposite the “side,” when the 
charge was a squat cylinder having a diameter equal to 
twice its height. 

Another series of trials, 225 using German 1,000-kg 
bombs of elliptical cross section, showed that the blast 
measured perpendicular to the major axis of the 
charge was more intense than that perpendicular to 
the minor axis. 

These blast measurements for bombs and small 
charges were made at relatively great distances from 
the charge, and, in many cases, asymmetries in the 
pressures were found as described above. Other mea¬ 
surements 226 of flame velocities very close to the 
charge (from which pressures could be computed) 
showed a marked asymmetry when cylindrical charges 
were used. Photographs of the shock wave 48 close to 
cylindrical bare charges with flat ends showed com¬ 
plicated wave patterns which were interpreted as the 
interactions of the shock waves from the cylindrical 
and plane parts of the charge. Several shocks could be 
observed, particularly off the corners and base of the 
charge. In the measurements of blast pressures oppo¬ 
site the base of cylindrical charges 92 the pressure¬ 
time oscillograms exhibited second and even third 
shocks closely following each other in the positive 
phase, in addition to the initial peaks. It can be in¬ 
ferred that these extra shocks correspond to the shock 
waves photographed very close to the charge. 

There is need for further work along these lines. 
The evolution of the shock waves from charges of sev¬ 
eral shapes, beginning at the surface of the charge and 
extending to large distances from it, should be studied 
systematically. 

The Blast Measured near the Breech of a 
Rocket Launcher 

Blast pressures were measured 227 near the jets 
from 5-in. spin-stabilized rockets in order to provide 
data that could be used in designing the mountings of 
such launchers on aircraft and other vehicles. It was 
thought that the air blast caused by the jets might be 
responsible for damage to exposed aircraft surfaces, 
for example. 

These measurements were made at various distances 




















108 


EXPLOSIONS AND EXPLOSIVES IN AIR 


behind the breech, and 6 to 18 in. off the axis of the 
launcher. One gauge, placed on the axis, and about 10 
ft behind the breech, recorded about 0.4 psi; the 
highest pressure measured was about 1 psi. The pres¬ 
sure-time records consisted of high-frequency (about 
6- to 10-kc) oscillations enduring for 100 msec or 
more. These oscillations were interpreted to be due to 
turbulence surrounding the jet. 

The Blast from Model Igloo-Type Explosive 
Storage Magazines 

The problem of storage of large quantities of high 
explosives became very acute at the end of the war. 
Existing magazine facilities were inadequate, and con¬ 
struction of new magazines would require greatly in¬ 
creased storage areas, if the previous standard inter¬ 
magazine distances were to be used. 

On behalf of the Army-Navy Explosives Safety 
Board, tests of the effects of full-scale magazine ex¬ 
plosions on adjacent magazines were carried out at 
Arco, Idaho, in the autumn of 1945. Blast-pressure 
measurements, as well as many other types of measure¬ 
ments, were made. “Target” magazines, placed at the 
standard spacing, as well as at proposed closer dis¬ 
tance from the exploded magazines, were found to sur¬ 
vive the blast. In order to study further the charac¬ 
teristics of explosions of igloo-type storage magazines, 
one-tenth scale model tests were carried out later at 
UERL. 

Reinforced concrete model igloos were constructed 
at the University of Illinois 228 under contract with 
Division 2, NDRC, and were tested by UERL. g In 
one test the igloos were arranged in a manner closely 
patterned after that used on the full-scale tests, and 
blast-pressure measurements were made. It was found 
that the blast pressures measured in these model tests 
were in good agreement with those of the full-scale tests, 
using the cube root scaling law. However, the damage 
to target magazines was more severe in the model tests 
than in the full-scale tests. Although this difference 
might have been due to failures to conform to the 
model laws or to differences in the construction details 
of the model and full-scale igloos, it is also possible 
that the greater damage in the model tests was due to 
a difference in the type of soil, with corresponding dif¬ 
ference in the earth shock transmitted. 

The model tests demonstrated that the effect of the 
earth cover on an exploded magazine is to reduce 
greatly the air blast from the explosion of its contents. 

g These results have not yet been formally reported. An 
informal report on one test is in reference 229. 


Tests simulating the piling of explosives in earthen 
revetments demonstrated that the revetment afforded 
little, if any, protection to adjacent igloos from the 
blast. The shape of the pile of explosives simulating 
that in an igloo (a long narrow pile), and also ar¬ 
ranged in a revetment in a less elongated pile, was 
found to affect the distribution of blast pressure 
around the charge. The pressures measured opposite 
the middle of the elongated pile were higher than those 
obtained opposite the side of the shorter pile. The 
presence of an earth cover, in other tests, also affected 
the asymmetry of the blast; the blast from the uncov¬ 
ered end with the door was found to be considerably 
more intense than that from the thickly covered rear. 
These observations might be useful in so arranging 
magazines that the strongest part of a target igloo is 
opposite the part of its neighbor from which the great¬ 
est blast intensity is expected. 

The probabilities of certain types of chains of sym¬ 
pathetic detonations in a magazine field have been 
computed for various probabilities that one magazine 
could be sympathetically detonated by the accidental 
explosion of a neighboring magazine. 230 It was con¬ 
cluded that, in a two-dimensional uniform array of 
magazines, if the chance that a single transfer will 
take place are one in five, say, the probability that no 
more than four magazines will explode is not less than 
0.53. The dying out of chains of sympathetic explo¬ 
sions in a magazine area cannot be counted upon as 
an insurance that no catastrophe will occur if the 
magazines are arranged uniformly in two dimensions. 

2.5 SOME PROPOSALS FOR FUTURE WORK 

The foregoing account of the theory and experi¬ 
ments dealing with air blast from explosives clearly 
shows that there is need for more work in this field. 
A few lines of investigation which seem necessary to 
improve existing knowledge of shock waves in air are 
indicated in the following. 

The applicability of the cube root scaling to point 
charge explosions and of square root scaling to line 
charges should be thoroughly studied, and, if these 
scaling principles are found not to be strictly applic¬ 
able, the causes of this failure should be investigated. 
This involves determination of the peak pressure and 
positive impulse versus distance curves over a wide 
range of distance from the charge and for a wide range 
of charge-weights. 

The afterburning phenomenon should be studied 
further, and an attempt should be made to obtain com- 






SOME PROPOSALS FOR FUTURE WORK 


109 


plete detailed information on the chemical processes 
that occur and the basic principles involved. After¬ 
burning should be studied using a variety of explo¬ 
sives. 

The effects on the blast of the shape of the charge, 
of the weight of case and of the material of which the 
case is made should be investigated, using a variety of 
explosive fillings. 

Comparisons with theoretical predictions of blast 
from explosive charges should be made, using both 
point and line charges, the measurements being made 
sufficiently close to the charge to test the existence of 
predicted maxima in the impulse versus distance 
curves. 

The pressures and impulses in all directions from 
line charges should be measured, and the effects of 
length of charge, cross sectional shape, and weight 
and material of case on the blast should be investi¬ 
gated. 

The properties of the negative phase (suction) 
from both point and line charges should be studied. 
The origin and properties of the “secondary” peak 
which is usually observed at or after the positive dura¬ 
tion time should also be investigated. 

The measurements of pressures and impulses from 
shocks obliquely reflected from plane surfaces should 
be continued and extended to include the whole ex¬ 
perimentally accessible region around an air-burst 
charge. Photographic studies of the reflections of 
shocks should be pursued further. 

The refraction of shock waves around corners should 
be explored, and the particular applications of this in¬ 


formation to evaluation and design of protective bar¬ 
ricades and to the penetration of blast into holes and 
slots should be made. 

The reactions of simple systems under blast loading 
should be investigated and theoretical work should go 
hand in hand with the experiments. The ultimate 
purpose of such work should be to establish well- 
defined criteria by which weapon effectiveness can be 
assessed. 

The subject of detonation in gaseous mixtures has 
been experimentally and theoretically attacked. Fur¬ 
ther work in this field, however, is needed. The air 
blast from gas-explosion sources should be measured. 

New experimental techniques are needed for much 
of this work. The condenser-microphone gauge is very 
promising for application where the use of piezoelec¬ 
tric gauges is difficult. Methods of pressure-time meas¬ 
urement very close to explosive charges must de¬ 
veloped. Apparatus for measuring transient tempera¬ 
tures and particle velocities would be very useful. Ex¬ 
isting photographic techniques should be improved 
and such measurements as explosion flame spectra at 
high speed undertaken. New mechanical gauges would 
supply much needed apparatus for certain purposes. 

These problems, and many others, have an obvious 
bearing on present or potential military applications. 
However, the study of air-blast phenomena should be 
undertaken, at least in part, with the point of view of 
acquiring a body of information which affords a really 
broad understanding of their nature and which pro¬ 
vides sufficient factual basis for development of 
weapons in ways not now foreseen. 


CONFI DENT l Al| 





Chapter 3 


EXPLOSIONS IN EARTH 


3i INTRODUCTION 

311 Object of the Investigation 

he primary purpose of the investigations described 
in this chapter was to determine the effect of sub¬ 
surface explosions on massive underground structures, 
such as fortifications, in order to provide a rational 
basis of design for structures to resist such attack and 
also to disclose the possibilities of such methods of 
attack on enemy structures. 11 The investigation of these 
problems was undertaken by the Committee on Pas¬ 
sive Protection Against Bombing [CPPAB] (later 
the Committee on Fortification Design [CFD]) of the 
National Research Council at the request of the Forti¬ 
fications Section of the Office of the Chief of Engi¬ 
neers, U. S. Army. This section of the Office of Chief 
of Engineers is charged, among other things, with the 
design of field and coastal fortifications. Up to the be¬ 
ginning of World War II, coastal and field fortifica¬ 
tions were designed to resist artillery fire. However, 
the advent of the long-range heavy bomber introduced 
an unknown element into the protection problem; 
namely, the effect of large quantities of high explo¬ 
sives detonated near to, or in contact with, the walls 
of a structure. The forces and their distribution about 
the structure are much different in this case from 
those produced by the impact of a projectile. Also, the 
probability of damage from a near miss by a bomb is 
much greater than that from a shell, even one of 
large caliber, since the shell carries a small amount 
of explosive compared to the bomb. A quantitative 
knowledge of the magnitude and duration of the 
forces imposed upon the structure by this form of 
attack is obviously very important to the fortification 
designer and was one of the chief objectives of the 
investigation. This information, once acquired, can 
obviously be used in reverse in order to formulate 
practical methods of attack on enemy installations. 
Some quantitative idea of the magnitudes of forces 
and the laws of propagation are essential to the plan¬ 
ners of aerial attack on targets such as bridges, dams, 
and underground installations in order that adequate 

a Pertinent to War Department Projects OD-03, OD-79, 
CE-5, CE-6, and to Navy Department Projects NO-12 and 
NO-263. 


sizes of bombs and density of attack be used to insure 
a reasonable chance of success. 11 

If industries and military installations are in the 
future placed underground to protect them against 
even more destructive explosives than have been gen¬ 
erally used, then the propagation of earth shock and 
its effect on structures becomes the primary concern 
of both the designer and the attacker of such instal¬ 
lations. 

312 Previous Investigations 

Before 1939, essentially the only systematic inves¬ 
tigations of the effect of underground explosions had 
been a study of the remote effects of quarry blasts, 
which had been undertaken by some explosive manu¬ 
facturers and the U. S. Bureau of Mines in order to 
establish the limits of distance for certain varieties 
of superficial damage to dwellings. 2 ' 7 These investiga¬ 
tions have had very little bearing on the problems of 
military damage but may be more valuable when 
future problems of protection are considered. 

In 1940 the problem of underground damage be¬ 
came of immediate and pressing interest to the Brit¬ 
ish, who initiated a program of experiments to deter¬ 
mine crater radii, earth movements, accelerations, 
and damage radii from bombs. These were more or 
less ad hoc experiments designed to furnish answers 
to pressing problems as they arose and did not attempt 
a systematic study of the phenomena. Considerable 
data were accumulated on the dimensions of craters 
and of the magnitudes of the earth movement, both 
transient and permanent, for various arbitrary depths 
of explosive charges. 8 ' 16 A series of controlled experi¬ 
ments was carried out at full scale on the damage in¬ 
flicted to underground piping and at a model scale 
on damage to buildings. 17,18 A survey of the state of 
knowledge at the end of 1941 concerning underground 
experiments is given in a report 19 containing some 
average curves for earth movement and wall damage 
as functions of distance and size of charge, together 
with an inference as to the validity of model laws for 
scaling results. 

The British had, of course, collected a wealth of 
information on damage to structures from actual 
bombing incidents, but the complexity of these re- 



110 


< ONFIDENTIA4 





INTRODUCTION 


111 


suits together with lack of knowledge as to the exact 
depth, point of impact, and frequently even the size 
of bomb, made correlation difficult and in some cases 
impossible. The interpretation of such data is aided 
greatly, of course, by a knowledge of the laws of varia¬ 
tion of underground effects with distance, charge size, 
depth of charge, and kind of soil which can only be 
obtained by systematic experimentation. 

313 The CPPAB-CFD, Division 2, 

NDRC Program 

It became evident in 1941, during the course of 
American experiments on bombing of fortification 
elements, that considerable damage to a fortification 
might be caused by a near miss penetrating into the 
earth adjacent to the structure and exploding there. 
This observation Avas consistent with the experience 
of the British on damage to foundation walls derived 
from actual bombing incidents. Proposals for protec¬ 
tion against such incidents by means of burster slabs 
and spaced walls were made and tried out at reduced 
and full scales. The results were sometimes quite un¬ 
expected and led to the conclusion that a systematic 
study of the phenomena occurring underground sub¬ 
sequent to the explosion of a buried bomb was neces¬ 
sary. The Humble Oil Company of Houston, Texas, 
at the conclusion of some discussions with members 
of the CPPAB voluntarily undertook to conduct some 
measurements on the transient displacements and 
pressures in earth at various distances from a buried 
charge of dynamite. 20 This work Avas preliminary in 
character and Avas mainly concerned Avith techniques 
of measurement of these quantities. The results A\ r ere 
sufficiently encouraging to Avarrant the continuance 
of the work Avith the purpose of investigating the ef¬ 
fects from larger charges, up to 1,000 lb of TNT. 21 
The results from these tests were difficult to interpret 
because the charges of different weights were not buried 
at depths proportional to the size of charge and be¬ 
cause, as Avas learned later, the soil in this locality had 
unusual transmission characteristics, coupled Avith the 
presence of a very shallow water table which gave an 
abrupt change of characteristics with depth. The re¬ 
sults of these experiments made it clear that the phe¬ 
nomena were indeed complicated and that only a 
large-scale systematic test which followed the prin¬ 
ciple of investigating one variable at a time Avhile 
holding all the others constant would yield the kind 
of data that Avould permit a quantitative evaluation 
of the influence of the various parameters. After cer¬ 


tain preliminary programs had been carried out at the 
Princeton Station of Division 2 to investigate prob¬ 
lems of instrumentation and choice of target types, a 
large program was organized for the systematic study 
of effects of underground explosions. 

The objectives of these projected experiments Avere 
(1) to determine the magnitudes of the measurable 
physical effects from an underground explosion as 
functions of distance, depth, soil type, size of charge, 
etc., (2) to measure the damage inflicted on a target 
model as a function of these same quantities, and 
(3) to obtain, if possible, a correlation between (1) 
and (2) in such a manner as to permit predictions to 
be made as to the damage that might be inflicted by 
a bomb or other explosive charge under a given set of 
conditions. An additional objectAe was that of ac¬ 
cumulating sufficient background information so that 
intelligent experiments could be planned for a par¬ 
ticular problem if objedAe (3) could not be com¬ 
pletely attained. 

The magnitude of this program greAV to alarming 
proportions as the final plans neared completion and 
it AA r as decided to omit the investigation of the depth 
effect and to place all charges at the scaled depth ex¬ 
pected to give maximum effects and damage as de¬ 
termined by preliminary experiments. The choice of 
a target model Avas attended by considerable perplex¬ 
ity but the problem Avas finally solved by the decision 
to use a target that simulated a structural element 
rather than a complete structure in the hope that an¬ 
alysis and application of the results Avould be facil¬ 
itated. The target chosen Avas essentially a reinforced 
concrete box without top or bottom and with massive 
side walls. An extensive construction program was 
initiated at Camp Gruber, Oklahoma, under the super¬ 
vision of the Corps of Engineers, designed to furnish 
a complete scale range of the selected type of target 
in order to determine, among other things, if any 
scale effect existed which would prevent the use of 
models to settle specific questions. It Avas essential in 
such a program, involving so much cost and labor, 
that as much information as possible be accumulated 
from each test, an objective that was greatly facilitated 
by the cooperation of the Geophysical Research Cor¬ 
poration of Tulsa, Oklahoma, and of the Humble Oil 
and Refining Company of Houston, Texas, in provid¬ 
ing personnel and equipment for recording transient 
velocities, displacements, accelerations, and earth 
pressures. This equipment Avas in addition to the 
Mobile Oscillographic Laboratory 22 and personnel 


CONTIDEXTTAL | 





112 


EXPLOSIONS IN EARTH 


provided by the Princeton University Station, Divi¬ 
sion 2, NDRC. The program involved the detonation 
of about 100,000 lb of explosive in units ranging from 
8 to 3,200 lb per shot and the construction of over 50 
target structures ranging in size from one-fifth to 
full scale. The full-scale targets had front walls of 5- 
ft thickness and 25-ft span, the other walls being 
identical in span but less thick. The experimental 
work started in August 1943, occupied about four 
months, and involved the taking of approximately 
10,000 records which were equally divided between 
transient measurements and those taken after the 
shot. The analysis of these data was completed in 
June 1944, at which time a report on the tests and 
analysis was rendered to the Office of the Chief of 
Engineers. 23 

At this time (June 1944) the CFD ceased to exist 
and Division 2, NDRC, undertook to continue this 
research particularly along the lines suggested in the 
above-mentioned report; namely, investigating the 
effect of soil type and depth of charge and gauge on 
the results. This involved no change in personnel or 
policies, inasmuch as the relations between Division 2, 
NDRC, and the CFD had always been very close and 
the personnel of the Princeton Station had directed 
and carried out much of the previous work. 

In order to carry out this second program, arrange¬ 
ments were made with the Humble Oil and Refining 
Co. to carry out investigations of the effect of charge 
and gauge depth in two radically different types of 
soil. One soil was the heavy clay found along the Oulf 
Coast of Texas and the other was loess, a light aeolian- 
deposited soil found in the vicinity of Natchez, Missis¬ 
sippi. Since the previous investigation had shown the 
model law to be obeyed, only one size of charge was 
used in this program (64 lb TNT). Concurrently with 
this work a parallel program was carried on at Prince¬ 
ton at a smaller scale to check the effects in a third 
type of soil. Also, a program of measurement of the 
comparative effectiveness of various kinds of explo¬ 
sives was carried out at small scale. 24 The experi¬ 
mental work in these programs was completed in July 
1945 and the analysis of the data completed in No¬ 
vember 19 4 5. 25 The interpretation of the results is 
handicapped by the absence of *any theory as to the 
propagation of explosion waves in a plastic material 
such as earth, but empirical analysis has succeeded in 
separating out fairly well the effects of the different 
parameters of charge and target geometry and the 
soil type from the data. A correlation with a simple 


theory of damage to structures has been made which 
gives the influence of some of the target and charge 
parameters on the degree of expected damage. (See 
also Chapter 15 of this volume.) 

32 PHYSICAL PHENOMENA IN EARTH 
THAT ACCOMPANY AN 
UNDERGROUND EXPLOSION 

3,21 Phenomena near the Explosion 

Detonation of a charge changes its solid material 
almost instantaneously into an equal mass of gas at 
very high pressure which immediately begins to ex¬ 
pand. This expansion imparts a high radial velocity 
to the earth particles adjacent to the charge and pro¬ 
duces a high transient pressure in the medium. The 
high initial velocity of the earth carries it past the 
point of pressure equilibrium, due to inertia, so that 
after a certain time the motion is arrested and a reverse 
motion is imparted. If the pressure in the gas bubble 
were not relieved the pressure at remote points would 
reduce to a value equal to the permanent stress in the 
medium due to the presence of this sphere of high- 
pressure gas. There are two factors that tend further 
to reduce the final pressure; one of these is the cool¬ 
ing of the gas in the gas bubble due to thermal conduc¬ 
tion to the medium and the other is the relief of pres¬ 
sure due to the break-through of the gas bubble to 
the surface of the e^rth, or to the leakage of the gas 
into the surrounding earth. If the charge is buried at 
such a depth that the gas pressure is quickly relieved 
by motion of the medium above the charge, the peak 
pressure will be reduced. This effect is illustrated in 
Figure 4, which shows the results of an experimental 
determination of the quantity called the coupling fac¬ 
tor of the explosive charge as a function of its depth 
below the surface. If the charge is within a certain 
depth, called the camouflet depth, the material above 
the gas bubble will be thrown out and a crater will 
be formed. A large proportion of the earth will, of 
course, fall back into the hole, thus masking the true 
dimensions, but excavations of craters have shown 
that the sides at and below the depth of the charge 
are highly compressed and discolored from the action 
of the hot gases in the bubble. 

3 - 2,2 Propagation of the Pressure W ave 

Earth in the vicinity of the high-pressure gas bubble 
acts as a plastic rather than an elastic medium which 
means that Hooke’s law is not obeyed and that the 





PHYSICAL PHENOMENA IN EARTH 


113 


strains are not proportional to the stresses. This char¬ 
acteristic of earth as a medium for the transmission 
of pressure waves is illustrated in Figure 1, which 
shows an experimentally obtained dynamic stress- 
strain curve for a certain variety of silty-clay soil 



Figure 1 . Experimental dynamic stress-strain relation 
for silty-clay soil. 


found in Oklahoma. The net effect of this plastic be¬ 
haviour of the medium is to cause pronounced distor¬ 
tion of the pressure wave as it is propagated away 
from the explosion. From the theory of wave propa¬ 
gation in solids discussed in Chapter 12 of this volume 
it is known that the velocity of an incremental pres¬ 
sure difference is proportional to the square root of 
the slope of the position it would occupy on the stress- 
strain curve, from which it can be readily seen that 
the velocity of the peak of the wave will be less than 
that of the initial part of the wave. The greater slope 
of the unloading portions of the stress-strain curve, 
except at very low pressures, indicates that the back 
of the wave has a higher velocity than the front. 

The effect of these properties of the stress-strain 
curve is that the wave suffers a continual change of 
shape in the rear as well as the front. The peak is 
simultaneously retarded with respect to the front of 
the wave and eaten away by the more rapid rarefac¬ 
tion part following it. The low speed of the tail of the 
wave results in an overall spreading out of the wave 


in space and time in addition to these other changes. 
These effects are shown in a series of experimental 
pressure-time curves in Figure 2. 

When these radial pressure waves meet the surface 
of the earth they are reflected with a reversal of phase. 
In practice, the wave is so spread out in time and 
space that this reflection is progressive and the re¬ 
flected part subtracts from the compression wave be¬ 
low it to produce an increase of attenuation of the 
pressure with distance near the surface rather than a 
clear-cut incident and reflected wave. The boundary 
conditions at the surface require the existence of an 



Figure 2. Typical pressure records at various distances 
from 8-lb TNT charges. 


auxiliary set of surface waves, sometimes called Ray¬ 
leigh waves. These waves travel at a lower speed and 
with less attenuation than the direct compressional 
waves and are responsible for the majority of surface 
effects at very remote distances from the explosion, 
such as window rattling and possibly plaster crack- 


( O.Vl-'IDKNTIAU 











































114 


EXPLOSIONS IN EARTH 


ing. The behavior of these waves is interesting from 
a theoretical point of view but since in the vicinity of 
the charge their magnitudes are negligible compared 
with the direct compressional waves, their importance 
in the study of military damage is minor. It may be 
that with large enough charges their effects at remote 
distances may move up into the military damage cate¬ 
gory but for normal explosives and bombs this is 
certainly not true. 

3 2 3 Effect of Soil Characteristics 

The magnitude of the transmitted pressure wave 
from an explosive charge is profoundly influenced by 
the properties of the soil through which it passes. Cer¬ 
tain soils, such as wet clay, are very good transmitters 
of pressure while other soils such as silty loam and 
loess are very poor transmitters of pressure. The ratio 
of transmissibility between the two extremes may be 
as large as 100 to 1. This large ratio does not mean 
that the radii of damage from bombs in soil are in 
these ratios but, as will be shown later, these damage 
radii have a maximum ratio of approximately 2 to 1. 
The transmissibility of soil is expressed quantitatively 
by a number called the soil constant k, which is cor¬ 
related roughly with the initial slope of the stress- 
strain curve and is ordinarily called the initial mod¬ 
ulus of elasticity, although the material is plastic and 
not elastic. The magnitudes of other phenomena in 
the medium, such as particle velocity, acceleration, 
transient motion, and impulse, are found to be pro¬ 
portional to some function of this soil constant, which 
thus turns out to be the quantity that is most descrip¬ 
tive of the propagation qualities of the soil. 

Referring to Figure 1, the stress-strain curve for a 
typical soil, one can deduce two facts, readily verified 
by experiment, which are (1) the finite area enclosed 
by the stress-strain loop implies that considerable en¬ 
ergy is dissipated per unit volume of material so that 
the waves must be rather rapidly attenuated, and (2) 
the displacement of the point of intersection of the 
unloading curve with the abscissas of the graph im¬ 
plies that the medium is left with a permanent strain 
or displacement after the passage of the wave. If the 
material were elastic, the peak pressure would decrease 
as the inverse distance, while experimentally it is 
found that in earth near the charge, the permanent 
displacement and the peak pressure decrease in magni¬ 
tude approximately as the inverse cube of the distance 
from the charge, indicating that the rate of energy 
dissipation in earth is very large. 

The magnitudes of pressure, acceleration, and tran¬ 


sient displacement near the crater may be very large. 
For example, in a typical silty-clay soil and for a 
1,000-lb charge of TNT, the peak pressure near the 
edge of the crater may be 1,000 psi, while the accel¬ 
eration is about 180 times the acceleration of gravity 
and the transient displacement may be as much as 
4 ft. 

The magnitude of pressure, acceleration, etc., inside 
the crater is not known except by inference, the reason 
for the uncertainty being the difficulty of making 
measurements in this region. Normally everything in 
this region is destroyed, including any equipment that 
may be placed there. 

3 3 THE MODEL LAW 

The model law, when referred to in connection with 
physical tests, is a term generally applied to a set of 
rules derived through dimensional reasoning by which 
the results of a set of properly designed experiments 
can be extended to larger or smaller scales of phenom¬ 
ena. The term scale effect has been somewhat loosely 
applied to any deviations from the model law that 
arise in an analysis of experimental results derived 
from models. The presence of such effects, which ap¬ 
parently do occur in some classes of experiments, such 
as those on projectile penetration discussed in Chap¬ 
ters 5, 6, and 7, greatly complicates the analysis of 
the results. Fortunately no such effects have been de¬ 
tected in underground explosion testing and the model 
law results can be extended with an accuracy as good 
as that of the original measurements. 

If it is assumed that the velocity of propagation of 
the effect of an explosion in earth depends only on the 
stress and not on such quantities as the rate of de¬ 
formation, then the effect of an increase in all dimen¬ 
sions of the experiment by the length scale factor S 
results in an increase of the time of propagation to 
an equivalent point by the same factor S. It is then 
possible to make a table (Table 1) in which any 
quantity such as pressure, impulse, velocity, etc., is 
represented by its dimensional components of mass 
M, length L, and time T, and to arrive at an expres¬ 
sion for the relative magnitude of this quantity in-the 
new system which is expanded in length scale by the 
factor S. In the present experiments W*, the cube 
root of the weight of explosive charge in pounds, has 
been selected as being a length characteristic of the 
scale of the experiment. This may seem dimensionally 
misleading but it merely means that there has been 
chosen for reference a unit of length whose cube is 





THE MODEL LAW 


115 


Table 1. Model law relations. 


Quantity 

Symbol and quantity 
in original 
system 

Scale 
factor A 

Quantity 
in the 
new system 

Length 

L 

S 

SL 

Mass 

M 

S 3 

sm 

Time 

T 

s 

ST 

Force 

F 

s 2 

S 2 F 

Pressure 

P, p 

1 

P, p 

Energy 

E 

S 3 

S*E 

Velocity 

u, V 

1 

u, V 

Total impulse 

P 

£3 

s*r 

Impulse per unit 

area 1 

S 

SI 

Displacement 

D 

s 

SD 

Acceleration 

a 

1/S 

a/S 


proportional to the weight or volume of the charge. 
Then if an experiment is performed with a charge- 
weight of W x lb and it is required to know the effects 
that would occur with a charge-weight of W 2 lb, the 
scale ratio S — (1E 2 /17i)^ and at the distance Sr, 
the magnitudes of the quantities in question can 
be determined from the original measurements at dis¬ 
tance r multiplied by the factors given in the table. 
The model law, of course, tells nothing of the manner 
in which the quantities vary with distance but states 
only that if the effect is of magnitude E x in the ex¬ 
perimental system at a distance r from the charge, 
then in the new system the effect will be AE X at a 
distance Sr from the charge, A depending on the 
quantity in question and being given in Table 1. 

An example that illustrates the use of the model 
law is the comparison of the peak pressures produced 
by the explosion of 1 and 1,000 lb of the same explo¬ 
sive. It is assumed that experiment has shown that 
at a distance of 4 ft from the 1-lb charge the peak 
pressure is 80 psi. The length-scale ratio between 
the two cases is (1,000/1) * = 10 and Table 1 shows 
that the scale factor for pressure is 1; consequently, 
at a distance of 40 ft ( = Sr) from the 1,000-lb charge 
the peak pressure is again 80 psi. This is equivalent 
to the statement that if r/W* is the same for the 
two cases then the pressure is the same. 

A comparison of the impulses per unit area 1 for 
these two weights of explosive at the scaled distances 

4 and 40 ft is made in the same way, except that, from 
Table 1, the scale factor for impulse per unit area is 

5 (= 10). Thus, if the impulse per unit area from a 
1-lb charge at 4 ft is found to be 0.2 psi-sec then at 
40 ft from a 1,000-lb charge the impulse per unit area 
is 2 psi-sec. This comes about by virtue of the fact 
that, although the peak pressures at these scaled dis¬ 
tances are the same, the time scale of the phenomena 


is multiplied by 10, the scale factor, so that the dura¬ 
tion of the pressure is increased tenfold. The impulse, 
being proportional to the product of pressure and 
time, must then be increased by a factor of 10 as in¬ 
dicated. 

It will be noted in this chapter that most of the 
experimentally determined quantities have been rep¬ 
resented by empirical equations which have as co¬ 
efficients a constant, and various combinations of the 
parameters k, W, p, r, and A. which are identified in 
Table 2. 

The manner in which these parameters enter into 
the empirical equations has been determined very 
simply by equating the dimensions on both sides of 
the equality sign. The variables were determined from 
physical considerations, but the manner in which they 
entered the equation was determined by dimensional 
considerations. The form of these equations was, of 
course, tested against the experimental data in each 
case and found to be correct to the first order of ap¬ 
proximation. The test for correctness consisted in 
determining to what extent the dimensionless constant 
in the equation really was constant for widely varying 
values of the parameters. 


Table 2. Parameters of the empirical equations. 


Symbol 

Name 

Dimension 

Units 

k 

Soil constant 

ML-'T- 2 

Psi 

W 

Charge-weight 

U 

Lb 

P 

Soil density 

ML-* 

Lb-sec 2 /in. 4 

lb per cu in. 

acc. g (in./sec 2 ) 

r 

Distance 

L 

Ft 

A 

r/W* 

1 

Dimensionless unit of 
distance from charge 


This section would be incomplete without a specific 
mention of target and damage relations to the model 
law. One of the primary objectives of the experimental 
program was, of course, to determine the accuracy of 
the model law as applied to target damage. The chief 
cause of the initial uncertainty was the fact that there 
are certain things in nature that do not scale, the chief 
offender being the effect of gravity. By changes of 
density of component materials efforts to overcome 
this defect can be made, but it is not easy to find 
structural materials of comparable strength and with 
greatly different densities. Consequently, if gravity is 
a controlling factor in an experiment, modification of 
the model law must be made. It was found experimen¬ 
tally, as had been inferred but not proved, that the 
impulsive forces involved in the damaging of a mas¬ 
sive structure are very large compared to gravity 


C O X FID E XT IA L 















116 


EXPLOSIONS IN EARTH 


forces, so that essentially no deviation from the model 
law was detected. The conclusion is then that struc¬ 
tural dimensions can be scaled, at least over a factor 
of 5 and probably 10, without encountering any devia¬ 
tion from the model law as far as explosive damage 
is concerned. 

34 THE characteristics of earth 

Earth as a transmission medium for mechanical 
effects is characterized as a nonelastic or a plastic 
medium. Its transmission properties vary with mois¬ 
ture content, grain size and shape, composition, his¬ 
tory, and possibly other factors. These effects combine 
to make the properties with respect to local position 
variable with depth, location, and weather. A 25 per 
cent dispersion in the measured effects from individual 
shots in a small area is the best consistency that has 
so far been attained. Reliable results can only be ob¬ 
tained by taking repeated measurements and averag¬ 
ing the results. In a region with variable soil types 
the individual results may vary by a much greater 
factor than 25 per cent. However, if the average soil 
constant of that locale is determined by a seismic 
method (discussed later) the results will not diverge 
very greatly from the 25 per cent consistency level. 

341 Wave Propagation 

The nature of earth as a transmission medium can 
be most readily understood by an examination of the 
stress-strain curve for a typical silty-clay soil. This 
stress-strain curve, which is shown in Figure 1, was 
determined by dynamic measurement described in 
detail elsewhere. 1 This figure shows that the slope of 
the loading part of the stress-strain curve decreases 
with an increase of pressure while the unloading part 
of the curve decreases in slope with a decrease in the 
pressure. The result of such a shape of the stress- 
strain curve is to produce dispersion in the trans¬ 
mitted eompressional wave in such a way as to pro¬ 
hibit the formation of a true shock wave. (See Chapter 
12 for discussion of wave propagation.) This is be¬ 
cause the decrease of slope at higher pressure levels 
corresponds to a lower propagation velocity for the 
peak of the wave than for the lower pressure levels. 
This is indicated by the equation 



In this equation p is the density of the medium 
(weight per unit volume divided by the acceleration 


of gravity), p is pressure or stress, 8 is strain, and v 
is the propagation velocity of the pressure level cor¬ 
responding to the point where dp/d8 is measured; 
consistent units must be used. 

This variable velocity causes a continual change of 
shape of the wave as it progresses away from the 
source as is discussed in the introduction to this chap¬ 
ter and in Chapter 12. 

The area between the loading and unloading parts 
of the curve of Figure 1 represents the energy ab¬ 
sorbed per unit volume of the soil passed over by the 
wave. This must cause an attenuation of the amplitude 
and energy of the wave as it progresses away from the 
charge. Calculations indicate that this energy loss is 
consistent with the experimentally determined rates 
of decay of pressure and displacement of the soil. 
The rate of propagation of the initial part of the wave, 
or of very small amplitude waves, is determined by the 
initial slope of the stress-strain curve. This corre¬ 
sponds to the velocity determined by seismic refrac¬ 
tion shooting. The fact that there is a rough correla¬ 
tion between the soil constant and the propagation 
velocity indicates that the general shape of the stress- 
strain curve is preserved in many soils even though 
the magnitude of the soil constant varies over large 
ranges. 

The density of the soil has only a small range of 
variation in comparison with the other parameters. 
The degree of compaction on the other hand has an 
appreciable effect on the stress-strain relation which, 
in a nonstratified medium, produces a continuous in¬ 
crease of velocity with depth. The effect of this con¬ 
tinuous change of velocity is to produce a curved 
transmission path. This was experimentally found to 
be the case in thick beds of loess encountered in the 
vicinity of Natchez, Mississippi. 25 

The moisture in the soil is probably the most im¬ 
portant variable and produces the greatest effect on 
the transmission of pressure. Moisture content can 
change rapidly with depth, particularly at the bound¬ 
ary of the water table. This rapid variation of veloc¬ 
ity produces refraction and possibly reflection effects, 
although these latter have not been definitely sepa¬ 
rated out of the data. The velocity of transmission 
through a water-soaked soil may be appreciably higher 
than the velocity through water itself. This corre¬ 
sponding high transmissibility appears in the data as 
a very high soil constant for wet soils. 

Another effect which appears to be a general one 
is the presence of a low-velocity layer very near to the 
surface of many soils. This effect is not thoroughly 







EXPERIMENTAL METHODS 


117 


understood but may be due to a layer of aerated and 
highly compressible soil near the surface which has 
inherently a low velocity, or it may be due to an up¬ 
ward bulging of the surface layer which retards the 
horizontal transmission of pressure. The attenuation 
of the pressure wave is greatly increased in this shal¬ 
low layer, as shown by the fact that the exponent of 
the pressure-distance curve (discussed later) changes 
from —3 to —4 in this region. 

A great amount of work has been done on the 
problem of predicting the soil transmission character 
from an examination of the grain sizes and distribu¬ 
tion, together with moisture content. The samples 
used were obtained by test borings. Core samples have 
been taken and tested for moduli of elasticity under 
rather careful control, 23 but the correlation of these 
results and the transmissibility of the soil as measured 
by explosion trials have proved very poor. It may be 
that the act of removing the soil from its place, even 
if carefully done, completely changes its stress-strain 
characteristics from those obtained in situ. The corre¬ 
lation of directly measured results with those obtained 
by seismic refraction shooting is very much better. 

The transmission properties of rock for very high 
pressures have not been studied with the same tech¬ 
niques applied in this work. Probably a systematic 
study would reveal many features common to both 
media; however, the closer approach to elastic condi¬ 
tions for rock would be expected to modify the results 
in many details. 

35 EXPERIMENTAL METHODS 

The physical effects, resulting from the detonation 
of an explosive charge underground may be divided 
into two classes: (1) transient effects which must be 
measured as functions of time, and (2) permanent 
effects which may be measured subsequent to the ex¬ 
plosion. 

The transient quantities are: 

1. Pressure. 

2. Impulse per unit area. 

3. Particle velocity. 

4. Particle acceleration. This may be measured 
directly or obtained by a time differentiation of 3. 

5. Particle displacement. This may be measured 
directly or obtained by a time integration of 3. 

6. Velocity of propagation of the pressure wave. 

The permanent effects which may be measured after 

the explosion are: 


7. Permanent earth displacement at or below the 
surface. 

8. Crater size. 

9. Damage to structures in the vicinity of the 
charge. 

All of the effects listed with the exception of 
6 and 8 can be measured on a structure underground, 
but the magnitudes of these quantities are determined 
by the characteristics of the structure as well as of 
the earth. 

The methods of measurement of these quantities 
are in general quite straightforward, although in 
most cases very elaborate equipment is needed because 
of the necessity for the simultaneous measurements 
of many quantities. Simultaneity of the measure¬ 
ments is desirable because the inhomogeneous nature 
of the medium, earth, makes impossible the exact 
repetition of any experiment. To obtain good correla¬ 
tion between quantities it is very desirable to measure 
them all from a single shot. An example of the efforts 
made in this direction was the systematic measure¬ 
ment of 32 transient quantities per shotfin the experi¬ 
ments conducted in Oklahoma. Of course, the results 
of many shots were averaged to obtain the perform¬ 
ance of the soil and structures but a factor character¬ 
istic of each shot can be obtained as a result of the 
number of simultaneous measurements. 

3 - 5,1 Testing Procedure 

The general experimental procedure is to drill a 
hole somewhat larger than the diameter of the explo¬ 
sive charge to the appropriate depth, place the charge, 
and fill the hole with water or thin mud as a tamping 
agent. The pressure gauges are placed at the bottoms 
of smaller holes drilled to the proper depth and the 
holes filled to the top with water. A slightly different 
procedure has to be used for the velocity and accelera¬ 
tion gauges, since it is found that for consistent re¬ 
sults these instruments must be cemented in place. 
The coupling to the earth appears to be variable unless 
this procedure is followed. This makes it extremely 
difficult to place these instruments at appreciable 
depths because of the recovery problem. For this 
reason almost all the measurements of particle veloc¬ 
ity and acceleration were taken at depths ranging 
from 6 to 18 in. from the surface. 

35 2 Transient Measurements 

The transient mechanical effects are translated by 
an electromechanical gauge, characteristic of the par- 







118 


EXPLOSIONS IN EARTH 


ticular quantity in question, into an electric charge or 
voltage which is amplified electrically and applied 
to a recording oscillograph. This may operate on 
either the electronic (cathode-ray) or the electro¬ 
magnetic principle. The time rate of variation of most 
of the quantities in small-scale work is great enough 
so that cathode-ray oscillographs are desirable record¬ 
ing agents, but for large charges high-frequency elec¬ 
tromagnetic or piezoelectric oscillographs may be used. 
The high-frequency requirements are less severe than 
are required for air-blast recording but the require¬ 
ments at the low-frequency end of the spectrum are 
slightly more severe. 

The records of the oscillograph deflections may be 
obtained on moving film or paper cameras, drum cam¬ 
eras with film or paper, or still cameras using a single 
sweep on the cathode-ray tubes. All these methods 
have been used, with film recording predominating 
for cathode-ray oscillographs [CRO] while paper re¬ 
cording is more often used for electromagnetic os¬ 
cillographs. 

Detailed descriptions of the apparatus used during 
the investigation reported here are given in published 
reports. 22,23 

The electromechanical gauges may in general be 
divided into three types; that is, (1) piezoelectric, 
(2) electromagnetic, and (3) variable-resistor gauges. 
A list of the measurable transient quantities together 
with the type of gauge used in its measurement is 
given in Table 3. 


Table 3. Measuring instruments. 


Quantity 

Gauge principle 

Pressure 

Piezoelectric, variable resistor 

Impulse 

Piezoelectric, variable resistor 

Particle velocity 

Electromagnetic 

Particle acceleration 

Electromagnetic, piezoelectric, 
variable resistor 

Particle displacement 

Electromagnetic 


The pressure gauges are of two types: (1) piezo¬ 
electric and (2) variable resistor of which the piezo¬ 
electric is the more successful, in general, although 
the variable-resistor gauges are more rugged and can 
be used closer to the explosive charge. The piezoelec¬ 
tric gauges are similar to those used in air-blast re¬ 
cording and consist of a stack of tourmaline crystals 
with appropriate electrodes and connections covered 
with a waterproof coating of rubber compound. Since 


these gauges are sensitive to hydrostatic pressure, no 
housing need be provided. The resistor gauges operate 
through the change of resistance of a coil of wire due 
to hydrostatic pressure. The coil of wire is housed in 
an oil-filled container to which the pressure is trans¬ 
mitted b)' a neoprene diaphragm. 23 This gauge is rug¬ 
ged but insensitive, the chief difficulty being the ten¬ 
dency of the oil column to be set into oscillation by a 
peaked pressure wave. 

The particle velocity gauges operate because of the 
motion of a coil in a magnetic field, the generated 
voltage being proportional to the velocity of relative 
motion. 22 These gauges have been very successful, in¬ 
asmuch as it is found that differentiation of their rec¬ 
ords gives values of acceleration consistent with direct 
measurements and the integration of the records gives 
values of displacement which are also consistent with 
directly measured values. Direct measurements of ac¬ 
celeration were made with piezoelectric and electro¬ 
magnetic accelerometers 1 of which the piezo type is 
the more useful because of its ruggedness. 

Transient displacement of the earth was measured 
by a coil on an inverted spring pendulum which was 
coupled to two coils excited in phase opposition. Dis¬ 
placement of the coil generates a voltage proportional 
to its displacement. 16 This instrument was quite suc¬ 
cessful, the chief difficulty being the necessity for ac¬ 
curate leveling and the change of damping constant 
with temperature. This was the only oil-damped in¬ 
strument used, the others being electromagnetically 
damped. 

Since all of the measured quantities, except pres¬ 
sure, are vector quantities, it is necessary to use all 
the instruments except the pressure gauges in pairs 
at each station, one to measure the radial horizontal 
component and the other to measure the vertical com¬ 
ponent. Only a single pressure gauge was used at each 
station. All piezoelectric gauges are subject to the vex¬ 
atious effect of cable signal which is the spurious 
charge generated in the insulation of cables when put 
into motion. Special cables can be obtained in which 
the effect is reduced to a minimum; in addition, pro¬ 
tection to these cables must be provided so that they 
are disturbed as little as possible by shaking and by 
falling debris. A cable manufactured by the British, 
called Telecon, seems to be the best so far obtained 
from the standpoint of absence of cable signal. 

Broad-band amplifiers with very long time con¬ 
stants must be provided for the recording of the elec¬ 
tric outputs of gauges, particularly the pressure 
gauges, since sometimes with big charges the effects 


Vox 111 iKNTI AJ 












RESULTS IN EARTH IN ABSENCE OF STRUCTURES 


119 


are of relatively long duration while for small-scale 
testing the times to the peak are frequently very short. 
These require cathode-ray oscillographs for their re¬ 
cording, but the particle velocities and earth motions 
are sufficiently slow for electromagnetic oscillographs 
of reasonably good frequency response to be used suc¬ 
cessfully. 

The multiplicity of amplifiers and recording chan¬ 
nels generally means that a special truck must be pro¬ 
vided to accommodate the apparatus both in transit 
and in use. 22 A separate gasoline-driven power supply 
of good regulation is necessary to supply electric cur¬ 
rent to the apparatus. 

3 6 RESULTS IN EARTH IN 

ABSENCE OF STRUCTURES 

361 Variation of Peak Pressure in Free Earth 

The pressure in earth from the detonation of an ex¬ 
plosive charge on or below the surface is propagated 
as a wave that is characterized by a continuous change 
of shape and length with distance from the charge. 
(See Figure 2.) This change of shape is a result of 
the spherical divergence of the wave and of the char¬ 
acter of the stress-strain relation of the medium which 
causes the higher pressures to be propagated more 
slowly than the low-pressure levels of the wave. (See 
Section 3.3 and Chapter 12.) 

The magnitude of the peak pressure of the wave is 
determined by essentially five factors: (1) the distance 
from the charge, (2) the character of the soil, (3) the 
coupling of the explosive energy to the soil, (4) the 
kind and amount of explosive, and (5) the depth of 
gauge if it is less than a critical depth. 

The general equation that is found to fit all the re¬ 
sults obtained in the range of distances 2 ^ X = 15 is 

P = FEk\~\ (2) 

where P — peak pressure in psi. 

X = r/W 1 = distance in feet divided by the 
cube root of the weight of explosive charge 
in pounds. 

h = a constant characteristic of the soil. 

F — a coupling coefficient determined by the 
depth of burial of the charge. 

E = an energy factor determined by the type 
of explosive. 

n — an exponent whose value is determined by 
the depth of the charge or gauge. 

The normal value of the exponent n is 3 except for 
depth of charge or gauge less than a critical value of 


approximately %W* ft. For depths less than this 
the exponent approaches the value 4. The cause of this 
increased attenuation near the surface is not very well 
understood but may be due to surface yielding or to a 



Figure 3. Peak pressure in earth as function of charge 
distance (1,000 lb TNT). 


CONFIDENTIAL 



































































120 


EXPLOSIONS IN EARTH 


reflection of the pressure wave from the surface in the 
opposite phase which reduces the peak-pressure level 
as the distance from the charge increases. The value 
of 3 for the exponent at depths greater than this criti¬ 
cal one is well established by many tests conducted in 
several different types of soil. Figure 3 shows the vari¬ 
ation of peak pressures from 1,000-lb TNT charges as 
function of distance factor A, obtained at Camp 
Gruber, Oklahoma. 

The explosive factor E has been determined for sev¬ 
eral types of explosives 24 with the results shown in 
Table 4. 


Table 4. Explosive factors for pressure. 


Explosive 

Explosive factor E 

TNT 

1.00 

Amatol 

1.04 

Comp. B 

1.04 

Tri tonal 

1.17 

Minol 2 

1.34 

HBX 2 

1.39 


For experiments using TNT, the explosive factor 
is unity and can be omitted from the equations. See 
Data Sheet 3B3 of Chapter 19 for summary of data 
on peak pressures in earth. 

The coupling factor F is a function of the depth of 
burial of the charge and is shown in Figure 4 with the 



Figure 4. Explosive coupling factor as function of 
charge depth in clay silt. 


abscissa in units of e/(ft)/\Ys(lb). This curve seems 
to have a maximum value at a depth of burial corre¬ 
sponding to d/W^ = 2 and to fall off rather rapidly 
at smaller depths and rather slowly at greater depths. 
The reason for the lower value at the more shallow 
depths is apparently due to the escape of gases before 
the material of the medium near the explosion has 
reached the limit of its outward expansion. It is be¬ 
lieved that for deeper gauges this fall-off at greater 


depths of charge will be more gradual or not even oc¬ 
cur. No data exist to prove or disprove this point, 
however. The most striking feature is the almost lin¬ 
ear rate of fall-off at charge depths less than the criti¬ 
cal depth of ft and the relative constancy 

for greater depth. 

For charges of TNT buried at depths of approxi¬ 
mately 21F^ ft and with gauges at a depth greater 
than %W$ ft the equation for pressure as a func¬ 
tion of distance reduces to 

P = A* A -3 . (3) 

This simple form of the empirical equation for va¬ 
riation of pressure with distance allows the transmis¬ 
sion characteristics of the soil to be expressed by a 
single parameter k, which is called the soil constant. 
If A is taken as a dimensionless variable, then k has 
the dimensions of a modulus of elasticity. The range 
of values of k encountered in the experiments repre¬ 
sents the variations in the soil if it is assumed that 
the same energy per pound of explosive is released at 
every shot. The assumption as to the constancy of en¬ 
ergy release in a properly boostered charge is verified 
by other explosive tests. Any systematic variation in k 
with the weight of explosive charge would be evidence 
of the presence of a scale effect. No such variation is 
detected in any of the data. 

The soil constant may vary over a range of more 
than 100 to 1, depending on the type and condition of 
the soil, whereas the coupling factor does not show a 
range of variation exceeding about 7 to 1. This fact 
indicates that the type of soil is the most important 
single variable governing the transmission of pressure. 


Table 5. Soil constants for pressure as function of soil 
type and location. 


Soil type 

Location 

fr(niin) fc(max) fc(avg) 

Loess 

Natchez, Miss. 

400 

1,700 

800 

Clay silt (loam) 

Princeton, N. J. 

1,300 

2,500 

2,000 

Silty clay 

Camp Gruber, Okla. 

1,300 

9,000 

5,100 

Clay, unsaturated Houston, Tex. 

10,000 

20,000 

15,000 

Clay, saturated 

Houston, Tex. 

50,000 150,000 100,000 


Table 5 shows measured values of the soil constant 
for different types of soil. See also Table 12 for a 
more extensive tabulation of soil constants based on 
measured seismic velocities. 

The general variability to be expected in soils can 
be seen from the range of the maximum and mini¬ 
mum values of k given in Table 5 for each soil type. 
This range of variation is probably due to local con¬ 
ditions of moisture content and composition. The 


( ONFIBEXTIAL 































RESULTS IN EARTH IN ABSENCE OF STRUCTURES 


121 


largest variable other than the type of soil seems to 
be its moisture content, a factor varying in a some¬ 
what unpredictable manner. In some localities the soil 
constant varies rapidly with depth (Figure 5). This 
has occurred in situations in which a shallow water 
table was present so that the moisture content and 
velocity of transmission varied over a large range 
quite near the surface. 


of ±25 per cent, is 


Jc = 




where h — soil constant in psi, 

lb per cu in. 

P = density of the soil =-> 

384 in. per sec 2 

v — velocity of seismic wave propagation in 
in. per sec. 



This equation has been found to hold within an aver¬ 
age accuracy limit of 25 per cent over a very wide 
range of soil types and values of the soil constant Jc. 

These correlations indicate that the general shapes 
of the stress-strain curves are similar in all the soils 
measured so far. The basis of this statement is that 
the peak pressure and consequently the soil constant 
is governed by the shape of the overall stress-strain 
curve, while the seismic velocity is indicative only of 
the initial slope. 

Exhaustive tests of soil properties at the site of ex¬ 
plosion tests made by the II. S. District Engineer 
Office at Tulsa, Oklahoma, have shown no satisfactory 
correlation between transmission of explosion waves 
and the characteristics of the soil determined by the 
customary methods of soil mechanics. 23 It may be 
that the act of removing soil for test, no matter how 
carefully performed, disturbs its elastic or plastic 
properties enough to give questionable results. The 
site of the tests contains soils of an extremely hetero¬ 
geneous character and the possibility exists that a 
more general study would yield positive results. 

Tests in the field have shown that the peak pressure 
exerted against a massive target due to reflection will 
be about twice the pressure in free earth. 13 


A correlation has been found between the soil con¬ 
stant Jc and the velocity of propagation of a seismic 
wave in the material. This is the velocity of a low- 
amplitude wave, corresponding to a sound wave in 
air, and is to be distinguished from the velocity of the 
peak of a finite wave. The initial slope of the stress- 
strain curve is associated with the velocity of very 
low-amplitude waves. The seismic velocity of these 
low-amplitude waves is obtained by shallow refraction 
shooting, using very small charges. This is a modifi¬ 
cation 27 of the technique used by geophysical pros¬ 
pectors in search for oil. Such explorations can be 
carried out very easily and cheaply compared to the 
direct method of measuring explosion pressures. The 
result of the correlation, which is accurate to the order 


3 . 6.2 Variation of Impulse per Unit Area 

in Free Earth 

The positive impulse per unit area of a pressure 
wave in earth is the forward momentum carried by a 
unit cross section of the wave and is given by the time 
integral of the pressure up to the time T 0 , at which 
the pressure falls to zero in the tail of the wave; i.e., 

/ To 

pdt. (5) 

Experimental determination of the impulse in free 
earth from the charge has shown that it obeys an em¬ 
pirical equation of the following form: 

J = E'FJc'W*\~ 5/2 (6) 


ionfide: 























122 


EXPLOSIONS IN EARTH 


where I — impulse per unit area in psi-sec, 

E' = explosive factor for impulse, 

F — explosive coupling factor (Figure 4), 

IF = a constant, characteristic of the soil 

type, 

IF* = cube root of the weight of charge, 

A = r/W* = distance in feet from the charge 
divided by the cube root of the weight 
of charge in pounds. 

The explosive factors E r do not have the same values 
for impulse as for peak pressures. This is not surpris¬ 
ing, since the impulse is more influenced by the be¬ 
havior of the gaseous products after detonation than 
is the peak pressure. With one exception, the explo¬ 
sives fall in the same order of merit but with slightly 
different ratios. This is shown in Table 6. 24 


Table G. Explosive factors for impulse. 


Explosive 

Explosive factor E' 

TNT 

1.00 

Amatol 

1.04 

Comp. B 

0.97 

Tri tonal 

1.27 

Minol 2 

1.38 

HBX 2 

1.50 


The explosive coupling factor F is the same as for 
peak pressure and is given in Figure 4 for the various 
depths of burial of the charge. 

As in the case of peak pressure, if the explosive is 
TNT and the depth of burial is of the order of 
2W * ft, then the impulse per unit area can be ex¬ 
pressed by the simple empirical equation: 

i = vw*xr*'*. (7) 

In this equation only one arbitrary parameter is 
present which may be associated with the transmissi- 
bility of the soil. The constant k' in this equation 
turns out to have a much smaller range of variation 
for different soils than does the soil constant l\ Its 
measured values are given for different soil tvpes in 
Table 7. 


pressure soil constant but still affords a rough guide 
to the magnitude of the expected impulse. The rela¬ 
tionship between //, p, r, and k with a probable error 
of approximately it 3 5 per cent is: 

IF = l.lopv — 5.5 (8) 

where V = soil constant for impulse, 

h = soil constant for pressure (Table 5), 
p = density of soil (lb-sec 2 per in. 4 ), 
v = velocity of seismic wave propagation in 
in. per sec. 

It is obvious that such correlations can be no better 
than rough guides to the transmission qualities of the 
soil. Nevertheless, in the absence of any better tests, 
these correlations are very useful. 

Consequently, equations (6) and (7) become: 


= 5.5E'FpikiW iX-*' 2 , 

(6') 

I = 5.5 pifcMF*A- 5/2 . 

(V) 


One would expect the impulse experienced by a 
massive target to be approximately twice the impulse 
in the incident wave. Experimentally, this ratio is 
found to be considerably more than 2, a phenomenon 
that has been explained qualitatively. 23 It comes 
about through the fact that the earth against the 
target may be left with a more or less permanent de¬ 
formation which may exert a residual pressure of long 
duration. This residual pressure in the tail of the 
wave is included in integrating the pressure as a 
function of time, with the result that the impulse is 
considerably increased. This ratio of reflected to direct 
impulse has been found experimentally to average 
about 2.8 to l, 23 but is subject to considerable fluc¬ 
tuation, since a relatively slight deflection of the 
target will relieve this residual pressure to a consid¬ 
erable degree. 

Figure G shows the variation of impulse with dis¬ 
tance from a 1,000-lb TNT charge. See Data Sheet 
3B3 of Chapter 19 for summary of data on impulses 
in earth. 


Table 7. Soil constants for impulse for various soils. 


Soil 

Location 

^ (avg) 

Loess 

Natchez, Miss. 

1.G0 

Clay silt (loam) 

Princeton, N. J. 

4.77 

Silty clav 

Camp Gruber, Okla. 

5.44 

Clay 

Houston, Tex. 

6.64 


The impulse constant Jc' has also been found to be 
correlated with the soil density and the seismic veloc¬ 
ity. The degree of correlation is not so good as for the 


Variation of Particle Velocity 
in Free Earth 


The maximum particle velocity of a wave is closely 
related to the peak pressure of the wave through the 
following equation (see Chapter 12 for further dis¬ 
cussion), 


1 


u = - 


P 



dp 

«■(/>)’ 



GONFIDILVI'IAL., 


















IMPULSE IN PSI 


RESULTS IN EARTH IN ABSENCE OF STRUCTURES 


123 


where u — the particle velocity in in. per sec, 
p — pressure in psi, 

P = peak pressure in psi, 

lb per cu in. 

P ~ the soil density = -, 

acc. g (in. per sec 2 ) 

v(p) = velocity of wave propagation in in. per 
sec as function of the pressure [equa¬ 
tion (1) ]. 


10 

7 

5 

3 


I 

0.7 

0.5 

0.3 


0.1 

.07 

.05 

.03 


3 5 7 10 

CHARGE DISTANC E ft/lb ^ 

(CHARGE WEIGHT)'/, ' 

Figure 6. Impulse in earth as function of charge 
distance (1,000 lb TNT). 



If the stress-strain curve is of the form indicated 
by experiment in clay-silt soil then the particle veloc¬ 
ity can be expressed as 


u 



( 10 ) 


where k = soil constant for pressure in psi (Table 5), 
A = r/W* (ft/lb*), 

P = density 

B = numerical constant which has the theo¬ 
retical value of 0.7 for this particular 
stress-strain curve. 

The maximum particle velocity measured by instru¬ 
ments on the surface of the earth is complicated by a 
general yielding of the surface, the reflection of pres¬ 
sure waves from the surface, and by the presence of 
surface waves that are necessary to satisfy the bound¬ 
ary conditions at the surface. These effects combine 
to give a functional form to the empirical expression 
for this quantity that is somewhat different than the 
derived expression above. 

In a particular series of tests these empirical re¬ 
sults are: 

u h = 7,050A -3 -f- 8.25A -1 in. per sec, (11) 

u v = 3,200A _3 + 9.85A -1 in. per sec, (12) 

where un is the maximum horizontal component of 
the radial velocity and u v is the vertical component. 
Since the components differ continually in phase and 
amplitude, the maximum value of the radial velocity 
cannot be found by a simple vector addition of the 
components. The difference of the value of the expo¬ 
nent of the leading term from the theoretically de¬ 
rived value is ascribed to the influence of the surface 
effects upon the wave amplitude and rate of decay. 
This assumption has not been verified, however, be¬ 
cause of the extreme difficulty of measuring the par¬ 
ticle velocities at appreciable depths below the surface. 
The expressions can be written in slightly more gen¬ 
eral terms since the average density and soil constant 
have been determined for the region in which these 
measurements were taken. Here p = 0.00015 lb-sec 2 
per in. 4 and k — 5,100. Then: 

u h = —r(1.2A -3 0.0015A -1 ) in. per sec, (13) 

P 5 

u v = -^t( 0.55A -3 + 0.0017A -1 ) in. per sec. (14) 
P 5 

Figure 7 shows experimental data on particle veloc- 


C 0 N F IDE NT I AH 















































124 


EXPLOSIONS IN EARTH 



Figure 7. Maximum particle velocities in earth as 
functions of charge distance (64 lb TNT). 


ity as a function of distance for 64-lb TNT charges. 

This graph and the empirical formulas give the ex¬ 
perimental values of the particle velocity at the surface 
resulting from the explosion of a charge of TNT 
buried at a depth of 2.1 TT* ft beneath the surface. 
Unfortunately, no data exist concerning the manner 
of variation with depth of burial of the charge or with 
type of charge. It is believed that these quantities are 
affected by the depth of burial in somewhat the same 
manner as the pressure, since there is a direct theo¬ 
retical relationship between pressure and particle 
velocity. In the absence of measured data then, one 
would apply the coupling factors and explosive factors 
to the particle velocity in the same manner as for 


pressure in order to obtain the most probable values 
for conditions other than those for which the data 
were taken. 

The theoretical value of the maximum particle ve¬ 
locity is appreciably less than that experimentally de¬ 
termined at the surface. This discrepancy is in the 
right direction since a reflection from the surface 
would be expected to give the surface particles a 
higher velocity than that predicted for particles at 
depths not affected by surface reflections. 

364 Variation of Particle Acceleration 

in Free Earth 

An extensive series of measurements in one location 
gave particle accelerations near the surface resulting 
from the detonation of charges of TNT buried at 
depths 2.1 IF* that can be expressed by the empirical 
equation 25 
Jc 

A g = -(120A- 4 + 0.3A -2 + 0.04A -1 ) X 10 -5 , (15) 

P W * 

where A g — horizontal or vertical acceleration in units 
of gravity (384 in. per sec- 2 ), 
k = soil constant in psi (Table 5), 

P = soil density (lb-sec 2 per in. 4 ), 

W = weight of explosive charge in pounds, 

A - r/lH, 

r — distance from the charge in ft. 

This experiment also showed that the variation of 
acceleration with depth of burial of the charge is the 
same as the variation in peak pressure so that the 
coupling factor derived from pressure measurements 
may be applied to particle accelerations. It is also 
inferred, but not directly shown by experimental data, 
that the acceleration varies with type of explosive in 
much the same way as does the pressure, so that the 
explosive factors for pressure can be applied to situa¬ 
tions in which explosives other than TNT are used 
(Table 4). 

The acceleration is, of course, a vector quantity 
that must be specified in direction or by components 
along a set of axes. Experimentally it has been found 
that at the charge depth used the horizontal and ver¬ 
tical components of acceleration are approximately 
equal to each other at every distance. The angle of 
emergence of the acceleration vector is consequently 
at 45 degrees to the surface. 

Figure 8 shows some experimentally obtained val¬ 
ues of acceleration as function of distance for 64-lb 
TNT charges which were measured in the Oklahoma 
tests. 


*.X K1DKXTIAL 



































RESULTS IN EARTH IN ABSENCE OF STRUCTURES 


125 



Figure 8. Maximum particle accelerations in earth as 
functions of charge distance (64 lb TNT). 


3.6.5 Variation of Particle Displacement 

in Free Earth 

The displacement of the particles in the medium 
due to the passage of a compression wave can be found 
by integrating the strain in each spherical shell over 
which the wave extends at the moment of maximum 
displacement. A first approximation is to assume that 
the maximum displacement of each particle occurs 
before appreciable negative velocity is attained by the 
particles. If this assumption is made, the displace¬ 
ment D at any radius r is, 



If one introduces the empirical pressure-distance 
and stress-strain curves, it is possible to derive an ex¬ 
pression of the following form for the maximum dis¬ 
placement : 

W* 

where A = r/W* , 

D = displacement in feet, 

W = weight of charge in pounds, 
k is given in Table 5, 
r — distance in feet. 

This displacement is presumably in a radial direction 
at depths below the surface. 

The experimental values of transient displacement 
derived from direct measurement and from integra¬ 
tion of the particle velocity-time records can be ex¬ 
pressed by the following empirical equation: 

D h = IfI(3.94A _3 0.0018A -1 ) ft (horizontal), (18) 

D v = 17^(1.05 A -3 -f- 0.0021A -1 ) ft (vertical). (19) 

The maximum horizontal and vertical displacements 
at the surface are not necessarily attained simultane¬ 
ously but, except at the greater distances, the displace¬ 
ments are approximately in phase. Then, approximate¬ 
ly, at the near distances one finds the total transient 
displacement to be 

D r = 4dT*A- 3 ft. (20) 

The value derived from equation (11), taking the 
average value of k to be 5,100, turns out to be: 

D r = 2.15U T *A -3 ft. (21) 

The ratio between these values is 1.86, which in¬ 
dicates that the assumptions made in the derivation 
are probably approximately correct. This rough deri¬ 
vation allows one to make estimates of the displace¬ 
ments for types of soil other than that in which the 
present measurements were made. 

Experiment shows that the permanent horizontal 
displacement is approximately one-third the maximum 
transient displacement given by the equation above. 
This is slightly less than would be indicated by the 
stress-strain curve, but again the effect of the surface 
introduces a modifying factor so that direct predic¬ 
tions from the stress-strain curve would probably be 
somewhat in error. 

If the dependence of displacement on the numerical 
value of k* [equation (11)] is accepted, then a plot 
of A vs (D/W&) (1 /k$) can be made which would allow 
estimates of displacements in soils with different 
values of k. Such a plot is shown in Figure 9 with 
horizontal and vertical components shown separately. 


k* A -3 


8 


(17) 


CONFIDENTIAL 









































126 


EXPLOSIONS IN EARTH 



1 2 3 5 7 10 20 30 50 70 100 


W 

Figure 9. Transient earth displacements at surface as 
functions of charge distance. Displacement in thousands 
of feet, weight in pounds, distance in feet, k as in Table 5. 


3 - 6 - 6 Crater Sizes 

The size of the crater produced by a buried charge 
has been shown experimentally to be much less sen¬ 
sitive to type of soil and kind of explosive than to 
the depth of burial of the charge. The exact mecha¬ 
nism of crater formation is not understood well 
enough to allow any theoretical predictions to be made 
concerning the factors governing the size, but it has 
been demonstrated quite conclusively that the model 
law is obeyed and that predictions of size based on 
empirical data are reasonably reliable. (See Data 
Sheets 3B1 and 3Bla of Chapter 19 for diameters and 
depths of earth craters.) 

The crater size can be considered to be equal to 
the product of an explosive factor E", of a depth fac¬ 
tor C, of a soil factor k" (which equals 1.3& 1/12 ), 
and of the cube root of the charge-weight, IFh 

The radius of the crater in feet is then 

i?(ft) = 1.3CE"k 1/12 WK (22) 

The explosive factors E" for some military explo¬ 
sives are given in Table 8. The factors are ratios of 
the radius of crater produced with the given explo¬ 
sive to the radius of crater produced by TNT. 



Figure 10. Depth factor for cratering by explosives. 


The depth factor (Figure 10) varies over a wider 
range than do the others. It displays a maximum value 
at a charge depth of approximately 2W* ft, descend¬ 
ing quite sharply toward zero as the charge depth 
approaches zero. The decline with increasing charge 
depth beyond the optimum is slower, but an extra¬ 
polation of the measured part of the curve indicates 
that at about 5Tfl ft the crater radius approaches 
zero with the formation of a camouflet. 

Figure 11 shows types of craters and the approxi¬ 
mate dimensions that might be expected from the 
explosion of a 500-lb bomb. 28 




.FRAGMENT SCARS_ 
* - ^ 


OEPTH OF TYPE 

BOMB AT OF 

DETONATION CRATER 

SUPERFICIAL 



OFT 
5 FT 

10 FT 

20 FT 


TYPE A 

TYPE B 

TYPE C 


o_ 

<0 


o_ 


o 


UJ 



30 FT 


PARTIAL 

CAMOUFLET 


O 

ro 


O 


O _ 
CM 


UJ 

< 

o 

<S) 


o. 


o - 3 


35 FT CAMOUFLET 


• • 
• * 
• • 




NOTE : BROKEN LINE 

INDICATES BLACKENED 
WALL OF CHAMBER 


CAMOUFLET 


Figure 11. Shapes and sizes of craters and camouflets 
for 500-lb GP bombs. 


CONFIDENTIAL 










































































































DAMAGE TO BURIED CONCRETE STRUCTURES 


127 


Table S. Crater radius as a function of type of 
explosive (ratios to TNT craters). 



CR X 

Explosive 

C1?tnt 

TNT 

1.00 

Amatol 

0.98 

Comp. B 

1.02 

Tri tonal 

1.11 

Minol 

1.14 

HBX 2 

1.15 


3 6 ‘ Comparison of Explosives 

The orders of effectiveness of different types of 
explosives for the production of various underground 
effects have been given in various tables throughout 
the report, but it may be desirable to collect these re¬ 
sults in one paragraph for convenient reference. Such 
comparison is given in Tables 9 and 10 where the 
values of peak pressure, impulse, crater radius and 
crater volume for the various explosives are compared 
to those for TNT at the same distance and depth of 
burial of the charge. The standard deviation of these 
ratios is approximately 5 per cent. 

The comparison in Table 9 is on the basis of equal 
weights of the explosive charges. If the comparison 
is made for equal volumes, slightly different values, 
which are shown in Table 10, are obtained because of 
the different densities of the explosives. For compari¬ 
son of effectiveness of bomb fillings, for example, 
where the volume is fixed, the comparison on an equal- 
volume basis is more useful. 


37 DAMAGE TO BURIED CONCRETE 

STRUCTURES 

/ 

From a military standpoint the physical phenomena 
in the medium, the laws of propagation, etc., are all 
subordinate to the degree of damage that will be pro¬ 
duced under a given set of circumstances. The solu¬ 
tion of this problem requires that satisfactory answers 
be obtained to two principal questions: (1) what are 
the magnitudes and durations of the forces acting on 
a structure and (2) what are the effects of such forces 
on a particular structure? These are extremely knotty 
questions, both of which involve a detailed knowledge 
of the behavior of structures under impulsive loads. 
The first and principal part of this chapter is con¬ 
cerned with the task of acquiring answers to the first 
of these two questions, and it is evident that no less 
effort must be spent on the answer to the second 
question. Some of these questions are treated in Chap¬ 
ter 15 of this volume. It is obvious that a complete 
answer would, in the limit, involve experiments with 
every conceivable type of structure which is, of course, 
an impractical procedure. It is equally obvious that 
some type of structure must be investigated experi¬ 
mentally in order to be able to make any predictions 
that are based on other than theoretical evidence. 

371 Description of Programs 

Two types of damage experiments were made. In 
the first of these, charges were detonated at distances 


Table 9. Comparison of explosives (equal weights, equal distances). 



Peak pressure of A” 

Impulse of X 

Crater radius of A' 

Crater volume of X 

Explosive 

Peak pressure of TNT 

Impulse of TNT 

Crater radius of TNT 

Crater volume of TNT 

TNT 

1.00 

1.00 

1.00 

1.00 

Amatol 

1.04 

1.04 

0.98 

0.95 

Comp. B 

1.04 

0.97 

1.02 

1.07 

Tritonal 

1.17 

1.27 

1.11 

1.39 

Minol 

1.34 

1.39 

1.14 

1.47 

HBX 2 

1.39 

1.50 

1.15 

1.51 


Table 10. Comparison of explosives (equal volumes, equal distances). 



Peak pressure of A" 

Impulse of A” 

Crater radius of A” 

Crater volume of A" 

Explosive 

Peak pressure of TNT 

Impulse of TNT 

Crater radius of TNT 

Crater volume of TNT 

TNT 

1.00 

1.00 

1.00 

1.00 

Amatol 

1.08 

1.09 

0.99 

0.97 

Comp. B 

1.12 

1.05 

1.04 

1.14 

Tritonal 

1.33 

1.47 

1.16 

1.55 

Minol 2 

1.44 

1.51 

1.17 

1.60 

HBX 2 

1.49 

1.63 

1.18 

1.63 


CONFIDENTIAL 


















































128 


EXPLOSIONS IN EARTH 


from reinforced concrete targets greater than one 
crater radius; and the pressures, accelerations, veloc¬ 
ities, and displacements on the target face and in free 
earth were recorded while the target damage was 
measured. In the other series of tests, charges were 
detonated in contact with the walls of buried, rein¬ 
forced concrete structures. No transient effects were 
measured. Damage was recorded and correlated with 
size of charge and thickness of wall. 


Damage from Noncontact Charges 

The great variety in fortification structures makes 
it impossible to select a typical target for study. Con¬ 
sequently, it was decided to use a target that would 
represent a structural element, rather than a complete 
structure. It was believed that the results obtained 
would in this case be more definite and at the same 
time more susceptible to theoretical analysis. If this 
turned out to be true, then extensions of the analysis 
to more complex structures would be practical. The 
structure finally selected for study after an extensive 
series of preliminary tests at small scale on various 
structure types, was essentially a reinforced concrete 
box with open top and bottom, represented in Figure 
12. The front and back were of different thicknesses, 
the latter being two-thirds of the front thickness. The 
side walls were of equal thickness and 0.42 as thick 
as the front. These targets were built in five sizes or 



Figure 12. Dimensions of scaled concrete targets. 


a ft 25S 
b ft 25S 
c ft 2S 
f ft 3S 
h ft 5S 


i ft 17.5S 
j ft 4S 
k ft 12.5S 
1 ft 3S 
m ft 12.5S 


Gauge positions in rear symmetrical with front. 


scales, namely, 0.2, 0.4, 0.6, 0.8, and 1.0, the last being 
the so-called full-scale target, intended for use with 
a 1,000-lb charge. The reason for the large number 
of sizes was to determine whether or not a scale effect, 
or consistent variation of effect with size of target, 
could be found. The absence of such an effect would 
make the use of small, inexpensive targets practical 
and reliable. 

In all, 16 targets of the 0.2 scale, nine of the 0.4 
scale, three of the 0.6 scale, seven of the 0.8 scale, 
and seven full-scale were constructed and tested. The 
magnitude of this project, which was carried out by 
the Tulsa District of the U. S. Corps of Engineers, can 
be visualized when it is realized that the full-scale 
targets were 25 ft on a side and 17 ft deep, with a 
front wall 5 ft thick and the other walls in proportion. 
The bottom of the target was 25 ft below ground level. 
The reinforcement of the full-scale targets consisted 
of a two-way mat of lVs in. square deformed bars at 
15-in. centers in each face of the front wall and com¬ 
parable reinforcement in each of the other walls. The 
average compressive strength of the concrete used was 
about 3,400 psi, measured on 6-in. cylinders. More 
detailed information on target characteristics and re¬ 
sulting damage are given elsewhere. 23 

On each target there were mounted three piezo¬ 
electric pressure gauges on the front face and one on 
the rear face, by means of which pressures were de¬ 
termined as functions of time. It was found that the 
pressure exerted on the front face of such a structure 
is approximately twice that measured in free earth 
at the same distance, and that the impulse per unit 
area is approximately 2.8 times that in free earth. 
The fact that impulse is more than doubled (one 
would normally expect more nearly exact doubling) 
is believed to be due to the packing of the earth against 
the front face of the target, resulting in a more sus¬ 
tained application of pressure than in free earth at 
the same distance. 

Thus, the pressure and impulse per unit area on a 
massive target in earth can be represented by the 
following expressions, provided normal explosives are 
used at depths of the order of 2IF* and at distances 
from the target between 2IF* and 15IF*, both in feet: 

P r = 2l-E\~ 3 , (23) 

I r = 15 p */b*F'F*A- 5/2 . (24) 

In the above equations P r and I r are the reflected peak 
pressure and impulse, k is the soil constant for pres¬ 
sure (Table 5), E and E' are explosive factors for 
pressure and impulse respectively (Tables 6, 8, 9, 10), 














DAMAGE TO BURIED CONCRETE STRUCTURES 


129 


A is r/W$ (r is distance in feet; W is charge-weight 
in pounds), p is density of earth in lb-sec 2 per in. 4 
and averages 0.00015. 

The term damage is qualitative and not susceptible 
to very definite measurement. A number of possible 
measures of damage were considered; among these the 
most significant are the total width of cracks in the 
front face and the amount of permanent bending of 
the front face. Both of these were used as measures of 
damage to the targets. 

The testing procedure was to detonate a charge at a 
predetermined distance from the front target wall, 
and to measure the crack widths and deflections of the 
front face, the pressure and impulse on the front face, 
and the acceleration given to the target. Simultane¬ 
ously, pressure, impulse, acceleration, and displace¬ 
ment were measured in free earth on the side of the 
charge opposite the target. Since the target is more or 
less damaged at every shot, it is apparent that only one 
set of measurements can be made on one target and 
that several targets must be used in order to obtain 
damage as a function of distance. 

Damage from Contact Explosions in Earth 

At the end of the test program described above the 
undamaged walls of the targets used in it were sub¬ 
jected to contact, earth-backed explosions. In addition, 
a series of tests on specially constructed targets was 
made at the same time. The latter tests were made at 
four scales on hollow reinforced concrete box struc¬ 
tures with floors and roofs. The scales were 0.2, 0.37, 
0.63, and 1.0. Three 0.2-scale structures were built 
and one each of the other sizes. The full-scale target 
was 47x47 ft in plan and 28 ft high. Its four walls 
were respectively 10, 11, 12.3 and 13.5 ft thick. The 
roof thickness was 9.5 ft and the floor thickness 4.75 
ft. The other targets were in proportion. Reinforcing 
steel was arranged in mats and amounted to about 75 
lb per cu yd. Concrete strength was 3,400 psi. The 
earth was excavated to about one-third the height of 
target and back-filled against the structure to its full 
height after construction. The full-scale structure was 
exposed to the effect of 2,000-lb general-purpose [GP] 
bombs (1,080-lb charges) exploded in contact at the 
center of each side. Underfloor explosions were also 
tried. 

After each test the dimensions of cracks and the 
area of interior surface scabbing were recorded. From 
the latter it was possible to determine the so-called 
scabbing limit of concrete walls subjected to contact 


explosion with earth backing. A more complete dis¬ 
cussion is given elsewhere. 23 

3 7 2 Representation of Results 

Damage from Noncontact Charges 

The results of this series of tests are best represented 
in a dimensionless plot showing either front-face crack 
width c or front-face deflection X c divided by a quan¬ 
tity of the same dimension, such as W*, as a function 
of the important independent variables, namely, W, 
distance from charge, a factor characteristic of the 
soil, and factors characteristic of the target. The most 



Figure 13. Total width of front wall cracks as function 
of distance and size of crater. Crack width in inches 
X 10 4 , weight in pounds, distance in feet, k as in Table 5. 


































130 


EXPLOSIONS IN EARTH 


important characteristic soil factor is k (Table 5). 
The charge distance is best expressed as A = r/WK 
Figures 13 and Id give the results obtained in this 
series of tests. The first shows c/kW 1 as function of 
A. Note that c is the total crack width in inches, and 



Figure 14. Permanent front wall deflection as function 
of distance and size of charge. Deflection in inches X 10 4 , 
weight in pounds, distance in feet, k as in Table 5. 

that k is the soil constant for pressure (Table 5). The 
other figure gives X c /kW$ as a function of A. It is 
significant that there appears to be no consistent de¬ 
viation with target scale. This indicates that target 
damage obeys the model law and that small-scale tests 
can be used for predicting the effects on full-sized 
structures. Straight lines have been fitted to these 
points by least squares. In Figure 13 the slope of the 
line of best fit is —4.52, and with 95 per cent con¬ 


fidence its slope lies between — 3.85 and — 5.19. This 
indicates that peak pressure is not the principal dam¬ 
aging factor since that varies approximately as the 
inverse cube of distance. The solid line shows the least 
squares fit and has the equation 

— . ( 25 ) 

kWi 250 

Similarly, the straight line of Figure 14 has the equa¬ 
tion 



kWi 300 


A theoretical analysis of the behavior of the struc¬ 
tures tested has been made and is discussed in the fol¬ 
lowing section of this chapter and in Chapter 15, 
Section 15.5.2. 


Table 11. Damage categories for 5-ft wall of box struc¬ 
ture and corresponding distances of 1,000-lb charge 
in earth for which k = 5,000 (Table 5). 


Damage 

Crack width 
(inches) 

Charge distance 

X 

Charge distance 
(crater radii) 

Heavy 

5 

2 

1 

Moderate 

1 

3.5 

1.5 

Light 

0.1 

5 

2.5 


Three categories of damage have been defined for 
the 5-ft reinforced concrete wall. These definitions in 
terms of crack width are shown in Table 11, together 
with the corresponding distances of 1,000-lb charges, 
assuming that the structure and the soil are similar to 
those of the present series of tests. When this is not 
the case, use must be made of Weapon Data Sheet 
6A5 of Chapter 19 or of an analysis corresponding to 
that discussed in Chapter 15. 

Contact Charges 

From the investigation of the effects of earth- 
backed contact explosions on reinforced concrete walls 
that were made at the same time, it was concluded 
that the scabbing limit, or thickness at which scabbing 
of the far surface of a wall barely occurs in case of a 
contact earth-backed explosion, is given by the follow¬ 
ing expression 

T = 1.4F*, (27) 

where T is wall thickness in feet and TF is charge- 
weight in pounds. 

3 . 7.3 Theories of Damage to Buried 

Structures 

There is a simple theory for predicting the extent of 
damage to a buried structure when exposed to a near- 
















































DAMAGE TO BURIED CONCRETE STRUCTURES 


131 


by explosion in earth. 230 In this approach it is as¬ 
sumed that the impulse acting on the front face of the 
target puts it into motion. The velocity of motion is 
proportional to the total impulse divided by the mass 
of the front face. The kinetic energy of the front face 
can then be computed. A fraction of this energy is 
assumed to be used in causing plastic deformation of 
the front wall; from this the amount of bending and 
the width of cracks in this wall can be calculated. At 
two points in this analysis undetermined proportion¬ 
ality factors are introduced. These can be combined 
into a single factor whose magnitude can be found 
from experiment and must be assumed to remain the 
same in other situations. This method gives a relation 
between crack width, A, charge-weight, and soil con¬ 
stant that is of approximately the same form as equa¬ 
tion (25), namely, 


JcW* 



(28) 


where Q is a constant, the utilization factor, to be de¬ 
termined experimentally. The value of k is given in 
Table 5. The strength factor S is given by the expres¬ 
sion 

2ad 2 N<rWi 
S = - 

LH 



where a is the thickness of the target wall in inches, d 
is the diameter of reinforcing bars in the target in 
inches, N is the number of bars in one wall that are 
stretched by the deformation of that wall, o- is the 
yielding stress of the reinforcing steel in psi, L is the 


/ 

horizontal span of the wall in inches, and II is its 
vertical dimension in inches. In order to make equation 
(28) agree with equation (25) Q must equal 0.06. 
From the way in which equation (28) was derived, this 
indicates that the crack width is only 6 per cent of 
what it would be if all the impulse in the pressure wave 
were used to produce plastic deformation. 

It should be pointed out that measurements of pres¬ 
sure and impulse have not been made closer to the ex¬ 
plosion than correspond to A = 2 or 3. Consequently, 
any attempt to develop an analysis based on these 
measurements must recognize this limitation on its 
applicability. It appears, in fact, that for very near 
or contact charges the damage does not follow the 
same law that would be predicted from the effects of 
explosions beyond one crater radius. This is well illus¬ 
trated in the curves of Data Sheet 6A5 of Chapter 19, 
which are almost horizontal in the region of small 
charge distances. 

Because the utilization factor Q is so small in this 
case there is considerable uncertainty when equation 
(28) is applied to any situation that differs very much 
in respect either to soil characteristics or to structural 
characteristics from the tests that have been made. 
For this reason it seemed desirable to make a some¬ 
what more elaborate analysis with the hope that a 
closer correlation between its predictions and the mea¬ 
sured effects might be attained. Such an analysis was 
made but, unfortunately, not in time to appear in any 
published report; consequently it appears in Section 
15.5.2 to which reference should be made. This analy- 


Table 12. Tabulation of constants for various soils. 


Soil type 

Seismic velocity 
(fps) 

min max 

Soil constant 
k (psi) 

min max 

Top soil (light dry) 

600 

900 

262 

590 

Top soil (moist, loamy silt) 

1,000 

1,300 

812 

1,370 

Top soil (clayey) 

1,300 

2,000 

1,420 

3,370 

Top soil (semiconsolidated sandy clay) 

1,250 

2,150 

1,510 

4,150 

Wet loam 


2,500 

.... 

5,600 

Clay (dense wet, depending on depth) 

3,000 

5,900 

8,850 

34,100 

Rubble or gravel 

1,970 

2,600 

6,400 

11,100 

Cemented sand 

2,800 

3,200 

9,700 

12,600 

Water-saturated sand 

.... 

4,600 

.... 

22,500 

Sand 

4,600 

8,400 

26,200 

87,000 

Sand clay 

3,200 

3,800 

10,000 

13,900 

Cemented sand clay 

3,800 

4,200 

17,800 

21,700 

Clay, clayey sandstone 

.... 

5,900 

.... 

45,000 

Loose rock talus 

1,250 

2,500 

1,750 

7,000 

Weather-fractured rock 

1,500 

10,000 

3,100 

140,000 

Weather-fractured shale 

7,000 

11,000 

63,000 

156,000 

Weather-fractured sandstone 

4,250 

9,000 

23,500 

116,000 

Granite (slightly seamed) 

.... 

10,500 

.... 

160,000 

Limestone (massive) 

16,400 

20,200 

390,000 

590,000 

















132 


EXPLOSIONS IN EARTH 


sis differs from the one that has been described in that 
the pressure pulse is assumed to continue during a 
large part of the deflection time of the target wall. 
The wall is assumed to be deformed continuously, at 
the same time exerting a force on the remainder of the 
structure which is pushed backward thereby. The in¬ 
ertia and passive resistance of the earth behind the 
rear wall of the structure are considered as well as the 
possibility of simultaneous plastic bending of the rear 
wall. 

3.8 RECOMMENDATIONS FOR 

FUTURE WORK 

Much remains to be done on both experimental and 
theoretical aspects of underground explosion phenom¬ 
ena. The importance of these problems is very great, 
inasmuch as future protection of critical installations 
from high explosive and atomic bombs will almost cer¬ 
tainly involve burial in the earth. A knowledge of the 
factors that affect damage to possible targets exposed 
to the effects of possible weapons will be equally im¬ 
portant to the attacker and the defender. The follow¬ 
ing problems appear to be the most important: 

1. Development of a reasonably reliable and simple 
theory for predicting the effect of an explosion in free 


earth and on a structure. In particular, this should be 
applicable at great distances from the charge, since 
the atomic bomb will be effective at very great dis¬ 
tances. Both plastic and elastic media (earth and 
rock) must be considered. 

2. Continuation of the experiments on wave propa¬ 
gation that have been discussed, with particular atten¬ 
tion to the following questions: (a) the propagation 
of waves in rock, (b) the propagation of waves pro¬ 
duced by explosion near an interface between rock and 
earth or by explosion in a stratified medium, and (c) 
the propagation of waves at large distances from an 
explosion occurring at a relatively small-scaled depth 
in earth with and without an underlying rock stratum. 

3. Continuation of the experiments on structural 
damage that have been discussed, with particular at¬ 
tention to the following questions: (a) the damage to 
relatively weak structures at great distances from an 
explosion, (b) the damage to structures at various 
depths of burial instead of nearly flush with the 
ground surface, as in the tests that have been made, 
(c) the relation between damage to complete struc¬ 
tures and to structural elements. (For example, less 
damage would be expected to an isolated section of a 
tunnel than to an equal length of the complete struc¬ 
ture, because of the difference in continuity.) 


ICQ^FIDEKTIAI*. 






Chapter 4 

MUZZLE BLAST, ITS CHARACTERISTICS, EFFECTS, AND CONTROL 


4i INTRODUCTION 

uring World War II medium-caliber guns with 
very high muzzle velocities and rates of fire were 
developed, and the trend continued toward an increase 
in these properties. 11 These high-pressure guns were 
at first used for defense against aircraft, but later they 
were adapted for use in direct fire against armored 
vehicles and pillboxes. Against these targets the guns 
were fired at low elevations, and soon offensive and 
defensive tactics were developed which required dig¬ 
ging in the gun so that at times the muzzle barely 
cleared the ground. 

With some guns that saw action in World War II 
the muzzle-blast problem had already become acute. 
On land the blast tore up the ground ahead of the 
muzzle and raised great clouds of dust that not only 
obscured the target but also revealed the gun position 
to the enemy. At times the obscuration problem be¬ 
came critical, for in direct fire the target must be seen 
and, when the target is a moving vehicle, the strike of 
the projectile must be sensed. A high rate of fire is a 
useless luxury when the gun is enveloped in a cloud 
of dust. At sea, wdiere the decks are crowded with 
high-velocity guns as a means of defense against air 
attacks, the blast effects of a ship’s own guns often 
produced more damage than that inflicted on it by 
enemy action. The crews were injured by the cumula¬ 
tive effects of the blasts and structures were heavily 
damaged. 

As muzzle velocities increase, limitations appear in 
the tactical uses of high-pressure weapons. A gun 
that injures its crew, tears up neighboring structures 
with greater certainty than enemy fire, reveals its posi¬ 
tion through excessive flash, smoke, and dust, while 
effectively concealing that of the enemy, obviously 
needs something to tone down its performance. With 
the development of new types of weapons, such as 
rocket projectiles, it would seem that the modern high- 
pressure gun is already obsolescent unless something 
is developed to suppress the violence of the blast. 

The only attachments that have been used to any 
extent in controlling blast in medium-caliber guns are 
muzzle brakes and simple cone or blunderbuss exten- 

a Pertinent to War Department Projects OD-154 and 
OD-160, and to Navy Projects NO-144 and NO-208. 


sions to the muzzle of some antiaircraft guns to re¬ 
duce the intensity of the flash. Silencers and compen¬ 
sators have been used on small arms. Muzzle brakes 
are not intended primarily to reduce blast effects in 
the neighborhood of the muzzle. They were originally 
devised as supplements to recoil mechanisms, though 
at present, when the design of recoil mechanisms of¬ 
fers no particular difficulties to the ordnance engineer, 
muzzle brakes are used primarily to reduce recoil en¬ 
ergy so as to permit the mounting of high-pressure 
guns on lighter carriages. 

Although work has been done on muzzle brakes in 
many places for many years, the Germans were the 
first, during World War II, to make extensive use of 
them. They introduced a variety of muzzle attach¬ 
ments but all these were eventually supplanted by the 
familiar 2-baffle brake which has been copied so ex¬ 
tensively by other armies. This brake is a simple, 
sturdy unit of medium efficiency. The British 
developed high-efficiency brakes for use on the 6- 
pounder and 17-pounder, but the back blast from 
these brakes was too severe on the gun crews, and they 
made extensive use only of a modification of the 
German brake. 

The only American brake put into the field in mod¬ 
erate quantities was the M2 brake on some of the later 
76-mm guns mounted on tanks and tank destroyers. 
Little thought was given to the development of muzzle 
attachments until late in World War II. This lack of 
interest was due to the conviction that existing recoil 
mechanisms w T ere adequate to absorb the recoil energy 
of the high-pressure guns. No great attention seems 
to have been given the possibility of reducing the 
weight of the mount through the use of a muzzle 
brake, and great objection was made to the blast effect 
produced toward the rear of the gun when any blast 
deflector is attached to the muzzle. Eventually, gun 
crews became accustomed to the back blast from the 
M2 brake on the 76-mm gun, and they were demand¬ 
ing the brake principally, it seems, because the Ger¬ 
mans were using it. 

A demand arose for the development of muzzle at¬ 
tachments when it was observed that under certain 
conditions the standard type of brake greatly reduces 
obscuration from dust, and some who had not felt the 



fcOXFUlENTIAG 


133 






134 


MUZZLE BLAST 


need of a brake, as such, advocated its use for the re¬ 
lief of the dust situation. Toward the end of World 
War II a few experimental mounts were designed in 
which a brake was an integral part of the assembly. 

Early in 1944, at the request of the Army Ground 
Forces, Division 2 agreed to attempt the development 
of a muzzle attachment that would suppress the rais¬ 
ing of dust. Contracts for this work were given to 
Princeton University, the General Electric Company 
[GE], and the California Institute of Technology. 
At the beginning it was decided that the three con¬ 
tractors were to work on different phases of the proj¬ 
ect. At the Princeton Station the development was to 
be attempted of a light attachment that could replace 
the standard brake as a field modification and that 
might possibly give immediate partial relief from 
obscuration; at GE a correlation was to be attempted 
between the properties of high-pressure transient jets 
and proper sequences of steady-state jets, a high-pres¬ 
sure steam “gun” emptying into an evacuated chamber 
being proposed; and at the California Institute of 
Technology the basic work for a long-range program 
was projected. This separation of the project was not 
always adhered to. For instance, while the steam ap¬ 
paratus was being assembled, GE engineers con¬ 
structed a medium-pressure .50-caliber air gun on 
which some 50 muzzle attachments were tested over a 
dust table. This turned out to be extremely valuable 
in arriving at conclusions about the potentialities of 
field attachments. 

The development of deflectors for the suppression 
of dust was to proceed without regard for the braking 
action of the attachments. Soon after the initiation of 
these contracts, Division 2 undertook to study the 
properties of muzzle brakes at the request of the Ord¬ 
nance Department, and the contract for this work was 
given to the Franklin Institute. 

As part of the muzzle-blast investigations under 
Division 2, Princeton University Station also accepted 
a contract for the study of the characteristics of high- 
pressure jets by the interferometric method. This work 
was undertaken at the request of the Bureau of Ord¬ 
nance of the Navy. 

During the progress of these investigations it has 
became apparent that recoil, obscuration from dust 
and smoke, and flash must be looked upon not as iso¬ 
lated problems, but as components of a muzzle-blast 
problem that must be considered in the design of 
gun and mount assembly. So long as one persists in 
thinking of solutions in terms of appliances which 


may be screwed on to the muzzles of existing guns the 
blast problem presents itself as a series of problems 
with more or less incompatible solutions. For instance, 
a high-efficiency brake may raise a great deal of dust 
and induce flash; a good diffuser which protects the 
ground from the severity of the blast may neverthe¬ 
less lead to serious obscuration; or a deflector that is 
effective in reducing obscuration may be a mediocre 
brake and induce flash in a normally flashless round. 
Since only one attachment may be used on a gun at a 
time, a more or less incomplete solution of only one 
of the component problems may be obtained or, at 
most, it may be possible to obtain only a small overall 
improvement in some group of blast effects, unless the 
drastic changes required to control blast as a whole 
are contemplated. 

The simplest problem pertaining to muzzle blast is 
that of the muzzle brake, if one disregards the other 
blast effects. The action is well understood and it is 
relatively a simple matter to design a brake of high 
efficiency. It is another matter, however, to utilize a 
high-efficiency brake; the braking action that may be 
utilized is limited by the back blast which the gun 
crew can stand. The problem of the utilization of high- 
efficiency brakes can be considered as the problem of 
rendering the deflected jet innocuous. This, however, 
is the problem of the control of blast as a whole, for 
if the deflected jet is made harmless, the blast of the 
gun is reduced to that of the weakened residual jet. 
The piping of the deflected gases through ducts paral¬ 
lel to the gun tube to where they can be expelled 
harmlessly to the rear of the crew or up over the car¬ 
riage presents no difficult engineering problems. The 
great problem that has been encountered is in the de¬ 
velopment of a deflector that reduces the forward jet 
to the magnitude where the superstructure is justifi¬ 
able. 

The necessity for resorting to extreme measures in 
controlling blast is seen in the failure of simple at¬ 
tachments to reduce blast effects satisfactorily. With 
increasing pressures and larger calibers the partial 
results now obtained become even less obvious. For 
instance, a diffuser that has been developed which 
eliminates the flash from a flashing round in the 76- 
mm gun produces no obvious effect on the flash of a 
90-mm gun. 

It is now possible to construct a deflector that re¬ 
duces the residual blast to that of an extremely low- 
pressure gun and that controls the deflected gases so 
that they can be piped backwards. 


iO\ KIPEXTIAl 





MUZZLE BLAST CHARACTERISTICS 


135 


*2 MUZZLE-BLAST CHARACTERISTICS 

The blast that follows shot ejection may be consid¬ 
ered either as a mild explosion or as an extremely 
high-pressure transient jet. It is a mild explosion with 
respect to the mass of the detonated charge. The gas 
generated by the burning of the powder expands con¬ 
siderably in the gun tube and loses a large fraction of 
its energy in accelerating the projectile to muzzle ve¬ 
locity before it is released into the atmosphere at shot 
ejection. However, the gas still retains a great deal of 
energy at this time. At the muzzle it is moving with 
the velocity of the projectile under a pressure of 500 
to 1,000 atm and heated to a temperature around 
1500 Iv. The time it takes the gun to empty is of the 
order of magnitude of the travel time of the projectile, 
about 6 msec in the 3-in. gun. The most obvious char¬ 
acteristics of the blast, as shown, for instance, by 
spark photographs, are a strong almost spherical air 
shock and, within it, the greatly expanded jet from 
the muzzle. The evolution of this jet is determined 
by the flux of gas out of the muzzle and, in its earliest 
stages, by the flight of the projectile which interferes 
with its formation; and the flux out of the muzzle is 
determined by the state and velocity distributions of 
the gas within the tube at shot ejection. 

4 - 2 * 1 Motion of the Gas within the Tube 

after Shot Ejection 

The problem of the emptying of a gun is the con¬ 
tinuation of the classical problem of interior ballistics 

-L 

that begins at detonation of the charge and ends with 
shot ejection. In some respects it is a simpler problem 
since there is practically no burning of the powder 
and the gas is expanding without the restraint of the 
projectile. The solution of this problem has been 
placed on a satisfactory basis. 1 ' 5 

Figure 1 shows typical pressure and velocity curves 
during the principal part of the emptying time. 
Curves 1 show conditions at the time of shot ejection. 
Because of the high temperature the velocity of sound 
in the gas behind the projectile at shot ejection is very 
high, generally higher than the muzzle velocity, so that 
the sudden pressure drop which occurs at the muzzle is 
propagated back against the stream as a wave of rare¬ 
faction. At the muzzle this wave moves slowly relative 
to the tube, but it acquires speed as it reaches the 
slower moving gas within the tube. Curves 2 and 3 
show the pressure and velocity distributions as the 
rarefaction front moves toward the breech, this front 
being marked b and c. Curves 4 show conditions as the 


rarefaction front reaches the breech, where it is re¬ 
flected and moves forward riding the outflowing gas 
until it comes out at the muzzle. Most of the emptying 
action takes place while this rarefaction front is in 



shot ejection. A. Pressure-distance distribution. B. Ve¬ 
locity-distance distribution. 

the tube. An important phenomenon occurs when this 
front emerges in the jet; a description of it will be 
given after the jet has been described. In the problem 
of the blast the important results are those that give 
the outflow of the gas from the muzzle. 

4 2 2 The Blast Characteristics 

The characteristics and evolution of the blast are 
known qualitatively, principally through spark photo¬ 
graphic studies of the burst from small arms and of 
high-pressure steady-state and transient jets. 5 " 7 

Figure 2 is a sketch showing the relevant features of 
the burst from a caliber .30 rifle firing service am¬ 
munition. The sketch is based on a spark photograph 
taken about Vs msec after shot ejection, when the 
bullet no longer interferes with the blast. 


COXITDEXTIAL 

























136 


MUZZLE BLAST 


The air shock that envelops the jet is marked a. The 
strength of this almost spherical shock is greatest in 
front near the bore axis and attenuates gradually to¬ 
ward the rear. As the shock front recedes from the 
muzzle the center of the surface moves forward along 
the bore axis because the surface elements where the 
shock strength is greater recede faster. 


As the gas crosses the oblique shock c, its speed is 
checked in the direction perpendicular to the shock 
surface so that the streamlines are violently deflected 
toward the bore axis. Most of the gas that crosses the 
shock c also goes through the oblique shock e, where 
the streamlines are deflected away from the bore axis. 
A typical streamline that crosses these shocks is 



The expansion of the jet takes place in the region 
marked b, which has been called the bottle. This bottle 
is bounded by the cylindrical oblique shock c and the 
normal shock d. The gas leaves the muzzle with the 
local speed of sound and expands freely as if there 
were no atmospheric constraint until it crosses the 
shocks. Within the bottle the velocity of the gas in¬ 
creases steadily as it moves away from the muzzle and 
becomes highly supersonic before entering the shocks. 


marked /. The stream becomes subsonic on crossing 
the normal shock d. The dotted line is roughly the 
boundary of the supersonic flow. The boundary be¬ 
tween the relatively slow-moving gas in the region h 
and the fast-moving gas in the region g is very sharp¬ 
ly defined near the intersection of the shocks. 

Surrounding the jet boundary there is a highly 
turbulent shell i in which the outer lamina of gas 
mixes with the outside air. At j this turbulent mix- 


CONFIDENTIAL 

























MUZZLE-BLAST CHARACTERISTICS 


137 


ing region forms a strong annular vortex called the 
smoke ring by analogy with the smoke rings blown 
out by smokers. This smoke ring is a vortex in the jet 
and need have no smoke in it, of course; when it does 
it can be seen clearly. 

In the region k close to the bore axis may be seen 
unburned powder particles traveling at very high 
speeds as indicated by their bow waves and wakes. 
Even in the stage of the burst shown by this sketch a 
few of these particles break through the traveling 
shock a into the still air ahead. 

A time photograph of the blast taken in a dark 
chamber will show a muzzle glow at i and a glow, 
called primary flash, in the region m behind the nor¬ 
mal shock. Neither of these is due to burning of the 
gases, since neither of these two regions comes in 
contact with the air. Muzzle glow and primary flash 
are observed even when the gun empties into a nitro¬ 
gen atmosphere. The same change in composition of 
the gases taking place within the tube which accounts 
for muzzle glow also accounts for primary flash. The 
action is inhibited as the gas enters the relatively cold 
bottle and starts again as the gas enters the normal 
shock, where the temperature rises to a value near 
that at the muzzle. The unburned powder particles 
no doubt contribute to the phenomenon by being 
heated to incandescence in going through these re¬ 
gions of high temperature. The burning of the powder 
gases, called secondary flash, which is the principal 
element of the flash in medium- and large-caliber 
guns, occurs in the turbulent mixing region. It begins 
in the forward region n of the smoke ring and travels 
backward until the whole turbulent shell is involved. 
The smoke ring continues to burn as it moves forward, 
so that a time exposure of the burst from a 90-mm 
gun, for instance, taken at night produces a carrot- 
shaped fogging of the plate some 3 tube lengths along 
the bore axis and 1 tube length across. 

In the earliest stages of the blast, from the time 
of shot ejection to the time when the projectile is 
10 to 15 calibers from the muzzle, the shock a takes 
on a variety of forms, depending on the condition 
of the tube. For instance, if the tube is worn so that 
gas leaks past the projectile while it is traveling in 
the tube, the early shock has the form of the outer 
surface of two intersecting spheres, the smaller one 
ahead of the bullet; if the tube is new the shock is 
open ahead of the projectile and does not close until 
the projectile is 4 or 5 calibers from the muzzle. In 
any case, by the time the blast has attained the stage 


shown in Figure 2, the shock smooths out into a 
nearly spherical shape. 

The jet cannot develop its characteristic shape, of 
course, until the bullet is beyond the point at which 
the shock cl would normally occur at the existing 
muzzle pressure. The expanding gas attains extremely 
high speeds and when the projectile is close to the 
muzzle a shock forms at its base; relative to the gas, 
the projectile travels toward the gun at supersonic 
speed. This shock eventually detaches itself from the 
base and becomes the shock d. In the .30-caliber fir¬ 
ings the shock becomes steady at a distance of about 
15 calibers from the muzzle. This distance is marked 
A in Figure 2. At first the diameter B is the greatest 
diameter of the bottle and is equal to A. The distance 
A remains constant while B shrinks until B — 0.5x4. 
While this is taking place the maximum diameter of 
the bottle drifts toward the muzzle and attains the 
final value C = 0.7x4. Beyond this point the bottle 
shrinks without appreciable change in shape. Since 
the rate of emptying of the gun is greatest at shot ejec¬ 
tion and attenuates very rapidly at first, the most 
damaging fraction of the blast comes out before the 
jet has attained a quasi-stationary shape. 

Spark photographs record only sharp changes in 
pressure and density. Small density changes can best 
be observed by interferometry. xAn interferometer is 
essentially an optical system that splits a beam of 
light into two beams and recombines them in such a 
way that corresponding points of the two beams co¬ 
incide finally. The interferometer is adjusted to give 
alternating zones of interference and reinforcement 
of light (fringes) on a photographic plate. If the 
density of the medium through which one of the 
beams passes is altered, a shift in these fringes is 
observed, the amount of the shift depending on the 
density change. If one of the beams is made to pass 
through a jet, a distorted fringe pattern is obtained 
from which the density distribution throughout the 
jet may be computed. x4 number of methods have been 
developed to obtain the density distribution from the 
observed fringe shifts. The computations are laborious 
and require the use of modern mechanical aids. 8,9 

By an extension of the results so far obtained on jets 
of moderate pressures, it is possible to draw a qualita¬ 
tive picture of the density distribution in the jet from 
a gun. Figure 3 shows this distribution at two sec¬ 
tions : A is the distribution along the bore axis, and B 
is that at a section through the bottle normal to the 
bore axis. Besides the fluctuations indicated behind 


CONFIDENTIAL! 





138 


MUZZLE BLAST 




Figure 3. Density distributions in jet. A. Longitudinal 
distribution. B. Diametral distribution. 

the shocks, minor fluctuations are observed within the 
bottle. These fluctuations lead to the waviness of the 
shocks observed in spark photographs and shown in 
Figure 2. 

By inserting probes into the jet it is found that 
the streamlines within the bottle, before they are 
deflected by the oblique shocks and in the regions not 
too near the muzzle, are practically straight and con¬ 
verge in a point on the bore axis close to the muzzle, 7 
as shown by the solid lines in Figure 4. The extension 



of these streamlines into the muzzle is indicated by 
the broken lines in the figure. 

Peak-blast pressures, as measured by gauges placed 
at varying distances from the muzzle, attenuate uni¬ 
formly with distance in the manner characteristic of 
all explosions. The scaling of blast pressure according 
to caliber requires a knowledge of the muzzle velocity 
and the state of the gas in the tube at shot ejection. 
The latter is not accurately known for most guns. 
Figure 5 shows the results of scaling the blast re¬ 
corded for a number of guns to .50-caliber scale. 10 


(- 

-) 


\ 

o 

1 1 - 

CALIBER .50,8 IN. ABOVE 
(AVERAGE APG FIRINGS) 

CALIBER 3.7 SCALED TO CALIBER .50 
(BRITISH) 

37 MM,24 IN. ABOVE PANEL, 2800 
FPS (PRINCETON) 

r.AI tRFR .SO n l/R PN ARAVF PANPI 

. \ 

o 



. ^ 

1 


x X. 

i \ 

V (x) 

1 

X 

2800 FF 

CAUSER .50 
2800 FP 

>S (PRINCETO 
,10 1/2 IN. AB 
S (PRINCETf 

N) 

OVE PANEL, 
3N) 

- 


X 

5 

‘\ 




- 







_1_ 

-1- 

■_ 1 _ 

.i_ 

« 


_1_ 


O 5 10 15 20 25 30 35 

DISTANCE D FROM POINT BENEATH MUZZLE FOR CALIBER .50 IN INCHES 

Figure 5. Attenuation of blast pressures with distance 
(.50-caliber scale). 

4 2 3 The Terminal Rarefaction 

The two curves marked 5 in Figure 1 show the state 
of the gas within the tube just before the rarefaction 
front reaches the muzzle after reflection at the breech. 
In Figure 6A the pressure curve is continued along 
the axis of the jet and beyond the normal shock. This 
shock is almost stationary relative to the tube but 
moving upstream with a relative speed determined 
by its strength. The rarefaction front will meet this 
shock at some point A. What happens after the en¬ 
counter may be seen by referring to Figure 6B. The 
top diagram shows a shock and rarefaction wave mov¬ 
ing relative to the still gas between them. The rare¬ 
faction front has a velocity c determined by the tem¬ 
perature of the gas into which the wave advances and 
the shock has a velocity V determined by this tem¬ 
perature and the ratio of the pressure before to that 
after it. The bottom diagram shows conditions after 
the encounter. The rarefaction wave is now traveling 
through the higher pressure gas behind the shock 
with a velocity c' — u 1 and the shock now moves with 
velocity F'-f - u 2 ; where u 0 , u 19 u 2 are the local 


CONFIDENTIAL, 









































BLAST EFFECTS 


139 


particle velocities, as indicated in the figure. Because 
of the nonlinearity of the flow the interaction of the 
two waves is not very simple, but roughly it may be 
said that the rarefaction gets through the shock with¬ 
out essential changes. 11 After the interaction the 
bottle attenuates more rapidly. 5,6 The rarefaction is 
propagated in all directions and superposes the veloc¬ 
ities behind it throughout the neighborhood of the 
muzzle. 


o 

tr 

u. 




B 

Figure 6. Terminal rarefaction in gun blast. A. Pressure 
distribution before emergence of rarefaction front. 

B. Interaction of shock and rarefaction wave. 

4-3 BLAST EFFECTS 

The effects of the blast near the muzzle are those 
of a mild explosion modified by the axial direction 
of the flow of gas, the interference by the projectile 
with the jet in the early stages of the blast, and the 
retardation of the outflow of gas by the length of the 
tube. For a given gun and type of projectile, muzzle- 
blast severity increases with muzzle velocity, but it 
is more accurate to consider the blast as a function 
of the charge weight, the projectile weight, and the 
ratio of the length of the tube to the caliber of the 


gun. Muzzle-blast effects increase with increasing 
charge mass and decrease with increasing length of 
tube, although increasing the tube length increases 
the velocity. 

431 Recoil 

The recoil of a gun is due to the backward pressure 
of the gas on the breech. Recoil begins at detonation 
of the charge and is ended by the action of the recoil 
mechanism. The recoil characteristics of a particular 
gun depend principally on the mount. For instance, 
the 37-mm antitank gun M3 recoils 20 in. whereas 
the 76-rnm gun mounted on the M18 vehicle recoils 
only 12 in. The recoil energy of a gun, however, de¬ 
pends on the same quantities that determine blast 
severity; that is, on the charge weight, the projectile 
weight, and the length of the tube in calibers. The 
recoil energy would be the kinetic energy of the re¬ 
coiling parts after the emptying of the gun, if these 
were mounted on level, frictionless runners parallel 
to the bore axis. Recoil energy is usually computed 
by equating the momentum of the recoiling parts to 
the momentum of shot and powder at the time of 
shot ejection; there is, however, an increment of en¬ 
ergy given the recoiling parts by the pressure on the 
breech during the emptying of the gun after shot 
ejection, which may be considerable in high-pressure 
guns. Recoil energy is most simply measured by 
mounting the recoiling parts on a free swinging 
pendulum. 4,12 ' 17 

The reduction of recoil energy by means of a muz¬ 
zle brake, as distinguished from the mere reduction 
of recoil length by a recoil mechanism, depends on the 
utilizable energy of the blast; that is, on the kinetic 
and available internal energy of the gas as it comes 
out of the muzzle. 

4 3 2 Blast Damage 

Damage to structures by muzzle blast is due prin¬ 
cipally to the effect of the sudden blast pressure, but 
close to the muzzle an important contributing ele¬ 
ment is the reversal in pressure that accompanies the 
terminal rarefaction. Near the muzzle the effects of 
this reversal are quite obvious. For instance, on firing 
a 3-in. gun at low bore heights over a blast mat, the 
pins that hold down the edges of the mat are often 
torn out and the loosened mat folded towards the 
gun. If enough pins are pulled out the mat may wrap 
itself around the gun. The edges of the mat may be 
tO feet from the muzzle when this happens. 


fcONFIDENTIAL' 























140 


MUZZLE BLAST 


The action may be visualized by considering a box 
with a closed lid, not hermetically sealed, placed near 
the muzzle. The initial blast pressure will tend to close 
the lid tighter and to crush in the walls. The peak 
pressure, however, is of extremely short duration and 
will merely give the walls and lid an initial inward 
impulse. The smaller but still high pressure behind 
the shock front will cause a flow of air into the box 
and build up the pressure inside. When the rarefaction 
wave comes, the lid will tend to fly open because of 
the relief of pressure outside which is of relatively 
long duration. WTien account is taken of the fact that 
most structures are stronger against pressure applied 
from outside, it will be seen that the rarefaction may 
account for a great deal of the damage of the blast. 

Injury to personnel from a single round is probably 
due to the peak pressures. A membrane as light as an 
ear drum may be broken by the impact of the shock 
wave. Repeated firings, even when the pressures are far 
below critical, produce more subtle effects. 

4 3 3 Dust and Obscuration of Target 

When a gun is fired over dry ground, a cloud of 
dust rises explosively near the muzzle. Fast motion 
pictures may be used to study the rise and motion of 
this cloud. 7 When the gun fires at low elevation and 
low bore height the blast scours the ground in a char¬ 
acteristic parabolic pattern. In the absence of wind 
the compact cloud takes on the motion of the blast; 
it drifts forward, expanding slowly, its outer bound¬ 
aries swirling in the direction of the vorticity of the 
smoke ring. Gravity eventually settles out the dust 
particles but this thinning out of the cloud may be 
very slow if the dust is fine. Any wind, of course, 
imparts its motion to the cloud and diffuses it. 

Though the motion and attenuation of the dust 
cloud may be recorded by motion pictures, the proc¬ 
esses by which dust particles are picked up and trans¬ 
ported cannot be observed; but the laws of mechanics 
that govern the motion of individual particles and the 
statistical laws that describe the average behavior of 
a large collection of particles are well known, of 
course. Theoretical studies have been made which 
lead to a satisfactory understanding of the scouring 
of the ground by the blast and the raising and diffu¬ 
sion of dust. 5,7,18,19 The principal conclusions re¬ 
garding the raising of dust by the blast are the 
following: 

1. Pressure changes in the jet and air contribute 
little to the motion of a dust particle except insofar 


as these changes cause the air surrounding the par¬ 
ticle to move. This statement is true even for strong 
shocks. 

2. In the absence of turbulence a dust particle al¬ 
ways has the velocity of the surrounding air super¬ 
posed on its characteristic settling velocity. 

3. The scouring of the ground is produced by the 
high-speed jet. Viscosity makes the air adhere to the 
surface particles. These are dragged with the current 
and act as an abrasive. 

4. Turbulence scours the ground and diffuses dust 
that it picks up, but these processes are relatively 
slow. The principal function of the turbulence is to 
keep dust in the air from settling out. 

5. Dust that has been picked up by the jet is held 
in suspension by the turbulence in the smoke ring 
and mixing layer surrounding the bottle and is trans¬ 
ported upward by the larger scale currents in these 
regions. 

6. Dust is picked up and may be raised a consider¬ 
able distance whenever a wave of rarefaction can 
penetrate the ground before complete reflection. The 
velocities of the air behind a wave of rarefaction are 
opposite to the direction of propagation of the wave 
and cause an explosive rising of the dust. 

The explosive rise of the dust caused by the ter¬ 
minal rarefaction can be observed in fast motion pic¬ 
tures. The amount of dust raised by this wave is 
considerably less than the amount picked up by the 
scouring action of the jet, but, coming after the main 
blast, it tends to stay close to the gun. The main 
traveling shock develops a rarefaction region behind 
it. On penetrating porous ground it raises dust a 
very small distance above the surface. This shock con¬ 
tributes to the raising of dust by preparing the ground 
for the blast that follows. 

The obscuration of the target by the dust cloud 
is by no means simply related to the amount of dust 
raised. Obscuration is characterized by its intensity 
and its duration. Both these elements are greatly 
affected bv meteorological conditions. A dense com- 
pact cloud that produces total obscuration may not 
be objectionable when a strong side wind sweeps it 
away quickly from the line of sight. On the other 
hand a diffuse dust cloud of great extent which pro¬ 
duces incomplete obscuration for a relatively long 
time may be quite objectionable. An extremely tenu¬ 
ous cloud may produce severe obscuration because of 
the scattering of light by the small dust particles, 
since the eye can distinguish only the contrast be¬ 
tween the transmitted and reflected light. 



PARTIAL CONTROL OF BLAST BY FIELD ATTACHMENTS 


141 


Since obscuration as it affects military weapons is 
a field phenomenon, the measurement of obscuration 
is a statistical field problem. The character of the 
obscuration associated with the blast of a particular 
gun is not something that can be determined in the 
laboratory; it is obtained as an average of the results 
of firing the gun under a great variety of field con¬ 
ditions. Since the larger guns must fire into fixed 
impact areas within small traverse ranges, it is diffi¬ 
cult to obtain an adequate variety of conditions. 

The obscuration due to a particular round may be 
measured in various ways. A direct and simple method 
is for one or more observers with stop watches to 
record the duration of total obscuration. This method 
is quite satisfactory when the gun is fired without 
muzzle attachment, for then the dust cloud usually 
has well-defined boundaries so that visibility is as¬ 
sured as soon as the cloud is swept away by the wind. 
If there is no wind the cloud attenuates as gravity 
settles out the dust and visibility continues to improve 
after the target is first visible. Muzzle attachments 
generally introduce secondary effects by dividing the 
jet; a period of clearing may be followed by a second¬ 
ary obscuration as the wind sweeps the dust raised 
to one side of the gun into the line of sight. Motion 
pictures, particularly with color film, taken at 32 or 
64 frames a second are fairly satisfactory in giving 
a permanent and general view of the phenomenon, 
but the analysis of a series of films is laborious and 
there is surprising variability in the results obtained 
by different observers. 

A rather elaborate method for measuring obscura¬ 
tion in the field has been developed. 4,5,20 An instru¬ 
ment which consists essentially of a phototube and 
a suitable current amplifier has been built around a 
Heiland recording oscillograph. A strong light, placed 
some 200 ft ahead of the gun, is focused so as to give 
a bright image on the phototube cathode, the instru¬ 
ment being placed behind the gun. To make a meas¬ 
urement, the light is turned on and the shutter ad¬ 
justed to give the proper current through the recorder. 
The light is then blocked off by a card to give the no¬ 
light trace on the record. When the card is removed 
the gun is fired. Thus the record shows full-light and 
no-light traces and the variable trace due to the dust 
that rises between the light source and the phototube. 
One channel of the recorder is used to make a time 
trace by driving it with a relaxation oscillator. Other 
channels are used with switches so that observers 
may record the time at which they first see the target 
and thus establish the visibility level of the record. 


The blast also contributes to obscuration in an ex¬ 
tended sense by causing the gunner to flinch; during 
the time it takes him to recuperate from the effects 
of the detonation the target is generally obscured and 
his sense of its direction impaired. Even when sight¬ 
ing through a telescope he may not be able to take 
advantage of brief intervals of clearing. 

4,34 Flash 

The flash from a medium-caliber high-pressure gun 
is brief but of great intensity. At night it lights up 
the surrounding country vividly and may produce 
complete blindness for a few seconds. Secondary flash, 
being produced by the burning of the hydrogen and 
carbon monoxide in the jet, is in effect a secondary 
explosion which increases the blast pressures. With 
high rates of fire, flash adds considerably to person¬ 
nel discomfort. 

44 the partial control of blast 

BY FIELD ATTACHMENTS 

When any device is attached to the muzzle of a gun 
it interferes with the free expansion of the jet. The 
thrust of the gas on the attachment modifies the re¬ 
coil energy of the tube, flash is affected by the change 
in shock pattern and the diffusion of the jet, the 
shape and concentration of the dust cloud and its 
obscuration characteristics are altered, and the dis¬ 
tribution of blast pressures near the muzzle are modi¬ 
fied by the change in the shape of the shock front 
and the redistribution of strength along it. The pur¬ 
pose of muzzle attachments is to produce favorable 
changes in some or all the above-mentioned effects. 

A distinction has been made between attachments 
that may be used on existing guns and those that re¬ 
quire more or less drastic changes in the construc¬ 
tion of the gun and mount assembly. The former are 
called field attachments. Strictly, no muzzle attach¬ 
ment is a field modification on a gun. Small devices, 
such as the service muzzle brake, require the cutting 
of a thread at the muzzle and the placing of a counter¬ 
weight on the breech block so as to allow the elevating 
mechanism to function freely. However, any attach¬ 
ment comparable to a standard muzzle brake in size 
and weight may be used as a field modification on a 
gun prepared to take the brake. The devices that may 
be constructed to modify the blast effects of a gun 
range continuously from simple field modifications 
to those that must be incorporated in the original de- 


fcOXFIDENTIAL, 








142 


MUZZLE BLAST 


sign of gun and mount; however, those devices will 
be called field attachments which require for their 
use only the cutting of a muzzle thread, the counter¬ 
weighting of the breech block, and the possible 
strengthening of the elevating mechanism. 

The reduction in blast effects that may be obtained 
by the use of field attachments can be expected at best 
to be incomplete, since through such devices the gas 
is still ejected in the neighborhood of the muzzle 
with little, if any, lengthening of the emptying time. 
It was seen that in a gun firing without muzzle at¬ 
tachment the greatest blast intensity occurs near the 
bore axis and tapers off gradually toward the rear. A 
blast deflector merely breaks up this concentration 
of the blast; it can do this in many ways, but it 
reduces the overall blast effectiveness only by the 
relatively small amount of energy made unavailable 
by the added shocks and turbulence which it produces 
and, perhaps, by the slight retardation of the jet when 
the deflector has a large capacity. Present knowledge 
of the deflection of a supersonic jet is qualitative and 
still meager. 4,5 

A field attachment that modifies the blast of a given 
gun satisfactorily cannot be expected to continue to 
show desirable properties when scaled up to higher 
calibers or when the powder pressure is increased. For 
instance, in the problem of obscuration, a device on 
the 76-mm gun that produces a transparent dust 
cloud may be acceptable even when it greatly length¬ 
ens the time of partial obscuration. A like deflector 
on a 90-mm gun may produce a comparable diminu¬ 
tion in the amount of dust raised, but the resulting 
cloud can produce complete obscuration for a greater 
time than does the cloud raised by the gun firing 
without attachment. A great reduction in the density 
of the dust cloud cannot be considered an improve¬ 
ment when the severity and duration of the obscura¬ 
tion are not diminished. 

The size of a deflector suitable for a field modifica¬ 
tion is greatly restricted. Upper limits were taken as 
10 lb for the 37-mm gun, 80 lb for the 76-mm gun, 
and 140 lb for the 90-mm gun. 21 In constructing 
small-scale models of these attachments it is usually 
difficult and impractical to construct an exactly scaled 
model, but if the scale is maintained the upper limit 
for the .50-caliber gun would be about 0.4 lb and for 
the .30-caliber gun about 0.08 lb. The sizes of the 
models built in the various projects involved in this 
program depended on the objectives of the particular 
investigations. At Princeton, for instance, the object 
was to develop a field modification for immediate use, 


and few models were designed and fewer constructed 
in the larger calibers that could not have been brought 
down to the proper weights by economical design; 
whereas at the Franklin Institute, where the inves¬ 
tigation was more basic, muzzle brakes were used on 
the .50-caliber gun which weighed 16 lb and were re¬ 
ducible to 5U> lb. 17 

441 Muzzle Brakes 

A muzzle brake consists essentially of a diffuser and 
a baffle. The diffuser is an extension of the muzzle 
which allows the gas to expand and guides it toward 
the baffle surface; the baffle is a plate which deflects 
radially the gas it intercepts. On being deflected the 
gas exerts a pressure on the baffle surface opposed to 
the pressure of the powder gas on the breech. This 
forward pressure counteracts to some extent the 
momentum of recoil. For a given gun the effectiveness 
of a brake depends on the fraction of the jet deflected 
and on the vector momentum of the deflected gas 
when it leaves the brake. Brakes are most successful, 
of course, on guns that have a severe blast. In high- 
velocity guns an appreciable increment in muzzle ve¬ 
locity is obtained only by increasing the charge con¬ 
siderably. 22 The greater powder pressure leads to 
greater recoil energy, but this increase is not so great 
as the increase in the available energy of the blast. 

A diffuser-baffle svstem with a number of variable 

*/ 

elements has been investigated at length on the .50- 
caliber gun. 6,12 ' 18 The generalized 1-baffle brake is 
shown in Figure 7. The effect on recoil of variations 
in the elements marked C, D, E, L, N, S in the draw¬ 
ing was determined. In this investigation the plate 
diameter Q of the baffles is large and the effect of vary¬ 
ing it was not considered. The flange around the 
diffuser, or nozzle, is not essential and in most of the 
brakes with non-zero reversal angle it was curved 
backward to permit free expansion of the deflected 
gas. 

A selection from the results of this investigation is 
given in Table 1. These results are for the flat 1- 
baffle brake and for the powder load adjusted to give 
a breech pressure of about 30,000 psi and a muzzle 
velocity near 2,500 fps. The last column shows the 
per cent reduction in recoil energy obtained by the 
various combinations of elements. This quantity is 

„ 100 (E 1 — E 2 ) 

where E 1 is the recoil energy of the gun firing with¬ 
out a brake and E 2 the recoil energy obtained when 


•XFIDENTIA L 







PARTIAL CONTROL OF BLAST BY FIELD ATTACHMENTS 


143 


Table 1. Effect of varying certain elements on the efficiency of a single-baffle brake, .50-caliber gun (D = 0, P = 30,000 psi). 


Group 

Variable 

s 

(calibers) 

C 

(degrees) 

L 

(calibers) 

E 

(degrees) 

N 

(calibers) 

R per cent 
reduction in 
recoil energy 

I 

Baffle 

0.5 

0 

0 


1.1 

31.4 


spacing 

1.0 

0 

0 


1.1 

55.1 


OS) 

2.0 

0 

0 


1.1 

65.8 



3.0 

0 

0 


1.1 

68.4 


Nozzle 

2.5 

0 

2.25 


1.1 

67.5 

11 

angle 

2.5 

10 

2.25 


1.1 

62.1 


(C) 

2.5 

30 

2.25 


1.1 

73.8 


L = 2.25 

2.5 

50 

2.25 


1.1 

70.0 

III 

Nozzle 

2.5 

0 

4.5 


1.1 

67.5 


angle 

2.5 

10 

4.5 


1.1 

63.3 


(C) 

2.5 

20 

4.5 


1.1 

70.8 


iQ 

II 

2.5 

30 

4.5 


1.1 

70.2 

IV 

Diffuser 

2.5 

30 

2.25 


1.1 

73.8 


cone 

2.5 

30 

2.25 

5 

1.1 

70.6 


angle 

2.5 

30 

2.25 

10 

1.1 

70.6 


(F) 

2.5 

30 

2.25 

15 

1.1 

70.6 

V 

Orifice 

2.5 

0 

2.25 


1.1 

67.2 


diameter 

2.5 

0 

2.25 

. , 

1.5 

62.8 


w 

2.5 

0 

2.25 

. . 

2.0 

55.3 



2.5 

0 

2.25 


2.5 

50.9 


the brake is used. The weight of the recoiling parts 
is maintained constant. 

Usually R is called the efficiency of the brake; 
but it must be borne in mind that it is the efficiency 
of the combination of gun, round, and brake. For 
example, a combination of muzzle-brake elements that 
leads to an efficiency of about 70 per cent on the 
.50-caliber gun, firing a round for which P — 30,000 
psi and v = 2,500 fps, yields an efficiency of only 
about 50 per cent when used on the .30-caliber rifle, 



Figure 7. Muzzle brake. The principal design variables. 


firing a service round 35 for which P > 50,000 psi and 
v — 2,700 fps. As has been pointed out, this variation 
in effectiveness is due to the difference in emptying 
characteristics of the two guns. 

The effect on efficiency of varying the powder load 
is indicated in Table 2. The first column {P — 30,000) 
shows the values of R listed for Group I in Table 1. 


Table 2. Effect on efficiency of varying powder load, 
flat 1-baffle brake without diffuser, .50-,caliber gun. 


S 

(calibers) 

R (per cent) 

P = 30,000 
(psi) 

P = 40,000 
(psi) 

P = 50,000 
(psi) 

0.5 

31.4 

34.0 

36.2 

1.0 

55.1 

55.3 

57.2 

2.0 

65.8 

67.9 

69.0 

3.0 

68.4 

70.4 

72.0 


From the point of view of the interception and 
deflection of the jet as well as from that of the design 
of brakes, a convenient parameter is 8 lf with M = 0, 
shown in Figure 7. For example, in Group IV of Table 
1 the efficiency of the brake is lowered by the addi¬ 
tion of a diffuser cone. b This reduction is observed 
when 8 -f- L, the distance to the back of the plate, 
is maintained constant. This result is to be expected 

b In this investigation the baffle orifice cone is called dif¬ 
fuser cone; however, with respect to the deflected gas it is a 
compresser. 35 


fcOSTFIDEXTIALf 






























































144 


MUZZLE BLAST 


since the jet is now intercepted nearer the muzzle 
where the expansion is less. Maintaining 8 X constant 
will show the effect of the diffuser cone on the de¬ 
flected blast. 5 Again, the third entry in Group II 
shows a significant gain in efficiency, as compared to 
the fourth entry in Group I, obtained by the intro¬ 
duction of a nozzle. However, in Group I, = S 
= 3 calibers and in Group II, S 1 = S -f- L = 4.75 
calibers, and at least part of this improvement must 
be attributed to the greater spacing. 

From the data obtained in these tests requirements 
for brakes of low, intermediate, and high efficiencies 
have been proposed. These requirements are shown 
in Table 3. 


Table 3. Muzzle brake requirements. 



Low 

efficiency 

Intermediate 

efficiency 

High 

efficiency 

Efficiency (per cent) 

30-35 

65-70 

86-91 

Number of baffles 

1 

1 

2 

No. 1 baffle spacing (caliber) 

0.5 

2-2.5 

9 

W 

No. 2 baffle spacing (caliber) 



1 

Reversal angle D (degrees) 

—30-4) 

0 

30-45 

Nozzle angle C (degrees) 

0 

15-20 

20-30 

Nozzle length L (caliber) 

0 

2.25-4.0 

2.25-4.0 


It should be observed that efficiencies ranging from 
87.4 per cent for P — 30,000 psi to 89.4 per cent 
for P — 50,000 psi have been obtained with a single 
baffle with D — 30 degrees. 16,17 

An empirical formula has been devised to predict 
the efficiency of muzzle brakes. The results obtained 
by the use of this formula agree quite well with the 
results of tests on the brake designs used in this in¬ 
vestigation, as is shown by Figure 8. The two curves 



4 4.5 5 5.5 6 6.5 7 7.5 

ANGLE OF RECOIL IN DEGREES 


Figure 8. Theoretical and observed variations in recoil 
due to variations in nozzle angle. 


of the figure, one for P — 30,000 psi, the other for P 
— 50,000 psi, show the computed and observed angles 
of recoil due to variations of the nozzle angle for a 
flat baffle spaced at 1.25 in. The known ballistic quan¬ 
tities used in this formula are net bore area, muzzle 
velocity, weight of recoiling parts, weight of projec¬ 
tile, and weight of charge; besides these, the muzzle 
pressure at shot ejection must be computed and the 



O 0.5 I 15 2 


BAFFLE SPACING S, in INCHES 

Figure 9. Muzzle brake. Effect on recoil of varying 

baffle diameter and spacing. 

mean muzzle velocity of the gases estimated or ad¬ 
justed to give results agreeing with experiment. The 
muzzle brake quantities are reduced to three areas and 
three angles which characterize the expansion and de¬ 
flection of the jet. These quantities are found from 
the geometry of the brake according to rules empiri¬ 
cally determined from results obtained with the .50- 
caliber gun. No comparison has been made with other 
calibers. 

The weight of a brake is greatly influenced, of 
course, by the plate diameter Q. As has been pointed 
out, the maximum weight of a field attachment suit¬ 
able for a given gun is severely restricted, and the de¬ 
sign problem starts with this restriction. A prelimi¬ 
nary investigation of the effects on recoil energy due 
to variations in Q has led to a number of conclusions 
concerning the construction of deflectors in general 
and brakes in particular. These tests were carried out 
with flat baffles on a .30-caliber rifle. 35 Some of the 
results obtained in this investigation are shown by the 
solid curves of Figure 9 where the recoil energy ob¬ 
tained by using single plates of various diameters is 
plotted against 8 lf the plate distance from the muzzle. 
The curve for the 5-in. plate envelops those for the 


t < i \ H UK VII \ 






























































PARTIAL CONTROL OF BLAST BY FIELD ATTACHMENTS 


145 


smaller diameters. Very near the muzzle all the 
curves coincide, showing that in that region the plate 
diameter Q — 0.75 in. is adequately large to yield the 
braking efficiency that can be obtained with baffle spac¬ 
ing^ not exceeding 0.13 in. At a spacing of about 0.13 
in., the curve for the 0.75-in. plate leaves the enve¬ 
lope, and the distance of the point of departure in¬ 
creases with increasing diameter. Beyond the point of 
departure all the curves are very much like that for 
the 1-in. baffle, which is plotted to S ± = 2 in. 

The effect of a second baffle is shown in the case 
where a 1-in. first plate is fixed 0.3 in. from the muz¬ 
zle. The dotted line in Figure 9 shows the recoil en¬ 
ergy curve obtained by varying the second baffle spac¬ 
ing. Some such investigation presumably led to the 
proportions of the German 2-baffle brake. 5 

From these results, aided by spark photographs of 
the deflected gases, the following general conclusions 
have been drawn regarding the size and effectiveness 
of brakes: 

1. If the length of a brake is fixed, then the greatest 
efficiency is obtained by using a single baffle of ade¬ 
quately large diameter. 

2. The weight of a brake may be greatly reduced 
by using two or more baffles within the fixed overall 
length. This reduction in weight is achieved by sac¬ 
rificing efficiency, but the reduction in efficiency is 
negligible when two baffles are used. 

3. The maximum amount of gas that may be uti¬ 
lized by any brake is close to that deflected by a single 
baffle of adequately large diameter placed at 4 calibers 
from the muzzle. 

A qualitative analysis of the flow through a deflector 
confirms these conclusions. 5 A type of brake designed 
on the basis of the results of this investigation is de¬ 
scribed in the next section. 

With the protection against muzzle blast afforded 
gun crews by existing guns, only brakes of medium 
efficiency can be utilized. The utilizable efficiencies 
may be obtained from light attachments, such as the 
2-baffle service brake used on the British 17-pounder. 

442 Deflectors for the Protection of 
Structures Against Blast Damage 

Any deflector that deforms the blast relieves blast 
pressures in some directions, accentuates them in 
others. Deflectors of moderate size may be used as aids 
in protecting structures only if there are directions 
available toward which the blast intensity may be di¬ 
rected. It is not sufficient, however, to deflect the blast 



Figure 10. Blast deflector for 20-mm A/C cannon. 


f t rv!'••!,rvn a ij 






























































































146 


MUZZLE BLAST 


from the structure to be protected; it is generally nec¬ 
essary, and always desirable, for the deflector not to 
enhance flash, which greatly increases the pressure ef¬ 
fects. It is always possible to deflect the gas unsym- 
metrically about the line of fire but when this is done 
a means must be provided to take up the eccentric 
thrust. 2 ' 5,23 ' 25 The possibility of protection against 
blast damage depends on the distribution of the struc¬ 
tures with respect to the gun position and the freedom 
in traverse and elevation of the gun. Thus the prob¬ 
lem of protection pertains to particular situations. 

Figure 10 shows a deflector designed to meet a par¬ 
ticular need. 5 This deflector terminates a blast tube 
attached to the muzzle of a rapid fire 20-mm cannon 
recessed in the wing of a fighter plane. The gun is 
close to the body of the plane and the blast effect is 
greatly accentuated by the flash enhanced by the pas¬ 
sage of the gases through the long tube. The taper- 
and-slot construction of the deflector concentrates the 
jet strongly in the vertical plane. The jet is fan 
shaped, with uniform distribution of flow and weak 
stationary shocks. In the model tested, flash was ef- 
fectivelv inhibited. 

This method of deflection was adopted instead of 
the usual baffle method because, for the proper me¬ 
chanical operation of the machine gun, it was neces¬ 
sary to minimize the braking action of the deflector. 

4,4 3 Deflectors for the Suppression 

of Dust 

The value of a deflector in relieving obscuration 
from dust can only be determined by extensive full- 
scale field tests. All field attachments produce obscu¬ 
ration at some time, depending on the terrain, the 
wind, and the weather, and most field attachments, 
under special conditions, produce longer periods of 
obscuration than does the gun firing without muzzle 
attachment. In order to compare the performances of 
various deflectors it is necessary to determine the rela¬ 
tive frequency with which they produce obscuration 
under a great variety of field conditions. No such com¬ 
plete series of tests has been performed. The adequate 
testing of deflectors was impeded because of the time 
and labor required to turn out full-scale models. 
Nevertheless, many deflectors were constructed and 
they were tested sufficiently to arrive at conclusions 
regarding the features which must be incorporated in 
a field attachment to yield optimum performance in 
the problem of obscuration. 4 ' 7,21 ' 35 

The passage for the projectile in a deflector allows 
a substantial fraction of the gas to go through and 


the residual axial jet is a source of obscuration. In the 
90-mm gun firing the present service round, the obscu¬ 
ration due to the residual jet alone is not objection¬ 
able when the deflector is equivalent to a flat plate 
with a hole 1.15 calibers in diameter placed at 4 cali¬ 
bers from the muzzle. To obtain this amount of de¬ 
flection with an actual deflector it is necessary that 
the ports be made sufficiently large to prevent the high 
pressure near the walls from drifting into the central 
part of the jet. 5 

The deflected jets produce secondary obscuration. 
To minimize this the jets should be directed back¬ 
ward, as in the service brake, and upward. The back¬ 
ward deflection simply reduces the region in which 
dust is picked up and thus gives the wind less oppor¬ 
tunity to carry the cloud into the line of sight. Up¬ 
ward deflection produces a downward thrust on the 
tube, consequently the amount of upward deflection 
that may be given the blast depends on the strength 
of the elevating mechanism. However, the amount of 
upward deflection that does not damage present ele¬ 
vating mechanisms has been found quite effective in 
reducing obscuration at normal bore heights, less so 
when the gun is dug in. 

The side jets should be made as homogeneous as 
practicable. A well-directed high-speed jet raises dust 
in a narrower area and blows it away farther from the 
muzzle than a diffuse turbulent jet. Besides producing 
obscuration a throttled jet tends to produce flash. 

At low bore heights the terminal rarefaction raises 
dust even when the jet does not strike the ground. A 
deflector with a large cavity tends to suppress the ef¬ 
fects of this rarefaction. However, a deflector with a 
cavity sufficiently great to be effective will have twice 
the maximum weight acceptable in a field attachment. 
Deflectors of large capacity tend strongly to enhance 
flash. 

Conical baffles with reversal angle of from 20 to 30 
degrees have been found most effective. Since maxi¬ 
mum deflection is required, nozzles are not desirable. 
This is true, at least, for rearward deflection not ex¬ 
ceeding about 30 degrees. 

The 2-baffle service brake modified so as to permit 
freer expansion of the gas between the muzzle and the 
first baffle and with the axes of the ports directed up¬ 
ward satisfies all the requirements for a deflector 
for the obscuration problem, except that of capac¬ 
ity. 5,23,24 n 0 deflector that has been constructed exceeds 
the performance of this modified brake in reducing 
obscuration. However, it induces severe flash and at 
low bore heights it damages a blast mat as much as 


* "M li'KXTl U\ 






PARTIAL CONTROL OF BLAST BY FIELD ATTACHMENTS 


147 


does the standard service brake. This last effect must 
be taken into account in the problem of dust because 
no field attachment can eliminate obscuration when 
the gun fires from the dug-in position. It is possible 
to prevent serious obscuration only by placing a suf¬ 
ficiently large blast mat under the deflector. If it is 
possible to dig the gun in it is certainly practicable to 
spread a mat before it. At low bore heights the prin¬ 
cipal function of the deflector is to protect the mat 
from the blast effect. 


What has been said regarding multiple baffling in 
connection with muzzle brakes applies equally well to 
all deflectors. This 4-baffle unit is about 25 per cent 
lighter than the 2-baffle deflector of comparable per¬ 
formance. It is not so efficient a deflector or brake as 
the 2-baffle unit, but the greater strength of the for¬ 
ward jet produces no noticeable effects on the dust at 
normal bore heights and its efficiency as a brake is 
probably as great as can be utilized when gun pres¬ 
sures exceed their present values. It shows a tendency 



SECTION A D 

(SECTION IS NOT A TRUE VIEW) 


Figure 11. Four-baffle deflector for suppression of dust. 


hibited the best overall performance in the tests to 
which it has thus far been subjected. 5,23,24 At normal 
bore heights its performance is not distinguishable 
from that of the 2-baffle unit, although close to the 
ground it produces somewhat greater obscuration. 
However, it showed marked improvement over all the 
deflectors tested in protecting a mat from blast dam¬ 
age at extremely low bore heights. It seems quite cer¬ 
tain that a properly constructed canvas mat can be 
used with this unit. 


The deflector shown in Figure 12 has a large cavity 
and the port area, although adequately large, is small 
compared to the wall area. 5,7 This deflector suppresses 
the effects of the terminal rarefaction quite satisfac¬ 
torily at low bore heights. As constructed, its general 
performance is not so good as that of other deflectors 
but it can be greatly improved by properly shaping and 
spacing the baffles. As has already been indicated, the 
suppression of the rarefaction wave is due to the large 
cavity and relatively small ports. The effectiveness of 























































































































































































148 


MUZZLE BLAST 



Figure 12. Deflector of large capacity for suppression of dust. 


any deflector in the dust problem is enhanced by a 
sufficiently great increase of its radial dimensions 
without an increase of the port area, but whether the 
improvement in visibility justifies the increase in 
weight has not been determined. Besides the disadvan¬ 
tage of increased weight, deflectors of large capacity 
induce flash. When firing flashless long-primer am¬ 
munition in the 76-mm gun, a brilliant flash was al¬ 
ways observed when the deflector shown in Figure 12 
was used. 

When the length of a deflector and the number of 
baffles is predetermined’ the diameter of the baffles as 
well as the spacing may be determined experimentally 
for maximum braking action as was indicated in con¬ 
nection with Figure 9. The port area then is made as 
large as practicable. In the 4-baffle deflector the baf¬ 
fles were spaced as shown in Figure 11 in an attempt 
to produce uniform flow through the ports rather 
than to give maximum braking action. A more effec¬ 
tive means of distributing the flow is to vary the diam¬ 
eters of the baffle holes as shown in Figure 12. This 
method, however, diminishes the efficiency of the unit 
as a deflector. Uniformity of flow can be achieved by 
varying the port areas as shown in Figure 13. 4 The 
capacity of this deflector is increased by increasing the 



(#39 ORILL) 




(#25 DRILL) ,200"X .400" 





Figure 13. Arrangement of ports to ensure uniform dis¬ 
tribution of outflow from deflector. 












































































































































































THE CONTROL OF BLAST 


149 


length without increasing the diameter. This deflector 
has received no full-scale tests. 


4.4.4 


Deflectors for the Suppression 
of Flash 


The suppression of flash and smoke is a problem 
of powder chemistry, but muzzle attachments have a 
great effect on the production of flash. It has been 
observed that multiple-baffle deflectors of small capac¬ 
ity and with small baffle hole diameters and large 
port areas tend to inhibit flash. The deflector shown 
in Figure 11 completely suppresses flash in the 37-mm 
gun, and an 8-baffle deflector similar to this completely 
suppresses the flash from a flashing round in the 
76-mm gun 80 per cent of the time. The flash pro¬ 
duced the rest of the time is weak and due to localized 
burning of the deflected jet. 5 ' 24 The 8-baffle deflector 
did not show any obvious diminution in the flash of 
the 90-mm gun, but the intensity of the flash from 
this gun is so great that even a great reduction could 
not be detected by the eye. 


45 THE CONTROL OF BLAST 

Satisfactory deflection of the gas may be achieved 
with relatively small muzzle attachments. The most 
efficient of these permit a residual jet to go through 
the forward hole which, by itself, produces unobjec¬ 
tionable blast effects in guns at least as large as the 
present 90-mm gun. The problem these deflectors leave 
unsolved is that of the disposal of the deflected jet. 
The most successful of muzzle attachments is the 
muzzle brake, but its usefulness is limited by the great 
blast pressures and other blast effects produced toward 
the rear of the gun when high efficiencies are utilized. 
The dust problem can no doubt be solved by using a 
sufficiently large attachment which deflects the jet 
straight up. Such a deflector would be a mediocre 
brake and, because of the great downward thrust at 
the end of the tube, its use would require radical 
changes in the gun and mount assembly with a sub¬ 
stantial overall increase in weight. So long as the 
blast, however deflected or deformed, is ejected in the 
neighborhood of the muzzle there will be muzzle-blast 
problems. 

Assuming that the desired fraction of the jet can 
be deflected through 180 degrees and carried in one 
or more ducts so as to eject it up over the carriage or 
sufficiently far to the rear of the gun, then near the 
muzzle the only blast effects would be those of the 
weak residual jet. In passing through the long ducts 


and through expansion chambers that might be pro¬ 
vided the deflected jet would lose considerable pres¬ 
sure ; the disposal system, in effect, could be an effec¬ 
tive muffler. The design of such a disposal system 
would present no grave difficulties. Consider, for ex¬ 
ample, the simple system in which the jet is subjected 
to an axially symmetrical deflection and the duct is 
the space between the outer surface of the gun tube 
and the inner surface of a concentric thin-walled tube 
of sufficiently large diameter. This duct would recoil 
with the gun and would have to fit into a second tube 
fixed to the part of the mount that moves as a unit 
with the recoil slide; that is, the first tube would re¬ 
coil with the gun into a second tube fixed to the mount 
but elevating and traversing with the gun. Beyond the 
juncture of the tubes the flow would be divided and 
carried by two ducts which might turn upward and 
possibly forward over the vehicle. The thrust produced 
by the secondary deflection of the gas could always be 
directed so as to produce no rocking of the carriage. 

Assuming the possibility of such deflection the 
maximum braking action would be available, and the 
saving in weight of recoil mechanism and mount 
would compensate for the weight of the disposal sys¬ 
tem. However, the silhouette of the gun would be in¬ 
creased. 

Such a disposal system can be justified only if a 
sufficiently large fraction of the blast can be turned 
through 180 degrees. One method of controlling the 
jet is to construct a valve that closes the forward hole 
of the deflector immediately after the base of the pro¬ 
jectile has gone through. A valve that shuts off the 
forward flow within 1 msec after shot ejection has 
been constructed for the .30-caliber gun. 5 The scaling 
of such a valve to large calibers presents difficulties, 
though not insurmountable ones. A valid objection to 
the use of such a device is that a valve is subject to 
malfunction. Deflection of a substantial portion of the 
jet through an angle greater than about 120 degrees 
by means of a static deflector has been found difficult. 
A 1-baffle deflector with cone diffuser of extremely 
large size can be constructed which gives satisfactory 
results, but multiple baffling to reduce the size leads 
to jet separation with consequent decrease in 
efficiency. 5 

Close to the termination of this investigation an 
efficient and reasonably compact 180-degree deflector 
was being developed. 5 The method of designing the 
inner surfaces of a 4-baffle unit is sketched in Figure 
14. The dotted lines a, b, c, cl and d f emanating from 
the mid-point of the muzzle are approximately the 








150 


MUZZLE BLAST 


asymptotes of streamlines in the bottle of the free jet. 
The lines cl, cl' are elements of the boundary of the 
minimum residual jet which goes through a circle of 
1.1-caliber diameter placed at 4 calibers from the muz¬ 
zle. This will be the actual residual jet, provided the 



Figure 14. The 180° blast deflector. Design of inner 
surfaces. Dimensions are in calibers. 


gas is allowed to expand freely at the muzzle and no 
shocks from the inner surfaces of the deflector enter 
the shaded region between d and cl', for an oblique 
shock that enters this region always deflects stream¬ 
lines from outside into the shaded area. To ensure 
that shocks do not enter this region or, if they enter, 
that they be weak it is necessary that the lips of 
the baffle cones be as thin as it is practicable to make 
them and that the elements of these cones coincide 
with the streamlines as closely as possible. From this 
initial direction the surfaces curve away gently so as 
to compress the intercepted gas gradually. 

The layout of the inner surfaces is still a matter of 
trial and experience since there are no known methods 
of ensuring the isentropic compression and turning of 
a 3-dimensional supersonic jet. It seems unlikely, fur¬ 
thermore, that a static deflector can be constructed to 
maintain isentropic flow at all stages of a transient 
jet. Practically, the compression and deflection of a 
supersonic jet can be accomplished only through a 
system of oblique shocks; these cannot be avoided, but 
if the compression is gradual it may be possible to 
turn the stream without producing a normal shock. 
The minimum requirement in the present problem is 
that a normal shock that may occur in the passage be¬ 
tween two baffles shall be weak enough not to drift 
down below the baffle cone lip, where it would alter 
the central flow. Once the gas is compressed to where 
its speed is subsonic it will follow the curved path 
more readily. The attempt to turn the gas as nearly 
isentropically as possible is desirable, however, for two 
reasons: (1) through adiabatic flow the greatest brak¬ 
ing action will be obtained, and (2) the tendency to 
flash will be diminished. 


After the gas is turned through 180 degrees it is al¬ 
lowed to expand into the ducts. The transition section 
also requires careful consideration. Even if it is not 
possible to maintain adiabatic flow, it is necessary 
that the transition be gradual to minimize turbulence. 
By maintaining a sharp boundary between the air in 
the ducts and the powder gas until the pressure is 
substantially reduced, secondary burning may be 
avoided. It is anticipated that burning within the dis¬ 
posal system and flash on ejection of the gases will 
prove troublesome to control unless, perhaps, a liquid 
spray is used within the system. 

The ideal spacing of the baffles is that which dis¬ 
tributes the flow uniformly between the passages. In 
view of the intensity of the flux of gas out of the muz¬ 
zle while the base of the projectile travels through the 
deflector it will be difficult to avoid an excess of gas 
going through the passages closest to the muzzle. The 
spacing shown in the sketch of Figure 14 is such as to 
make the openings normal to the mid-streamlines ap¬ 
proximately equal. 

The only deflector of this type constructed was a 
2-baffle brake with 30 degree reversal angle. 5 The re¬ 
sidual jet was about the weakest that has been ob¬ 
tained even though the width of the passages had been 
reduced to 0.07 in. at the point where the gas had 
been turned through 120 degrees. It seems quite cer¬ 
tain that through this small area the speed of the gas 
was already subsonic and that no loss in flow would 
have resulted from further turning. The braking effi¬ 
ciency was 68.5 per cent. It has already been explained 
that brakes on the .30-caliber rifle have low efficiencies 
and that a brake configuration that yields 50 per cent 
efficiency on this caliber will yield 70 per cent on the 
.50-caliber gun. Since there can be no throttling of 
the gas in the passages as there is in brakes with 
large baffle spacings, the efficiency will increase with 
increasing reversal angle and with proper expansion 
before ejection. 

46 CONCLUSIONS 

The blast problems that arise with increasing pres¬ 
sures in the modern medium-caliber high-velocity 
guns require for their solution a detailed knowledge 
of the phenomena associated with the emptying of a 
gun if the solution of these problems is to be raised 
from the trial and error stage. Methods of treating the 
interior ballistics of a gun after shot ejection have now 
been developed and a working knowledge, mostly 


• nN I I l >I-'. X I I A.L 






























RECOMMENDATIONS 


151 


qualitative, of the blast characteristics has been accu¬ 
mulated. Simplified formulas on which to base the 
rational design of muzzle attachments are still to be 
developed; but progress has been made in the under¬ 
standing of the extent to which muzzle-blast effects 
may be modified by various types of attachments, and 
general predictions regarding the efficacy of new de¬ 
signs can now be made. 

The most successful muzzle attachments are the 
muzzle brakes, but because of the high blast pressures 
they produce at the rear of a gun only brakes of me¬ 
dium and low efficiencies are generally utilizable. 
These may be constructed as light units. So long as 
only moderate braking efficiencies are required, attach¬ 
ments may be constructed that inhibit flash or, at 
least, that do not accentuate it. Freedom from obscu¬ 
ration of target is more difficult to ensure, but the seri¬ 
ousness of the problem may be diminished. By taking 
advantage of the strength of the elevating mechanism, 
the blast may be turned slightly upward and this is 
sufficient to reduce obscuration substantially at nor¬ 
mal bore heights. At low bore heights, slight upward 
deflection is insufficient to ensure visibility of target, 
but by proper diffusion of the deflected jets it is pos¬ 
sible to use a mat in combination with the deflector 
so that obscuration will result only under most ad¬ 
verse conditions. These improvements can be expected 
to be less obvious when the powder pressures are in¬ 
creased substantially above their present values. 

The full utilization of the breaking action of the 
blast and a more definite solution of the blast problem 
in general may be achieved by disposing of the gases 
toward the rear of the gun or up over the carriage. A 
disposal system of this sort must be incorporated in 
the design of gun and mount assembly. Since full¬ 
braking action is utilizable in this scheme, the great 
reduction that may be made in the weight of recoil 
mechanism and mount may be sufficient to allow a 
reduction in weight of the whole assembly. High- 
pressure guns can be rendered practically recoilless 
by the use of such a disposal system. 

By properly shaping the inner surfaces of the de¬ 
flector the blast can be delivered to the return ducts 
without tendency to burn, but it is not certain that 
burning would not occur as the gas mixes with the 
air in the ducts. To prevent burning it might be nec¬ 
essary to use a spray. In field guns the transportation 
of sufficient liquid to prevent burning would present, 
perhaps, a grave problem, but at sea the problem of 
spraying the gas in ducts would be minimized should 
salt water prove suitable for the purpose. 


Since the equivalent of the obscuration problem 
does not occur at sea, it should be possible to obtain 
a substantial reduction of the blast effects in a ship’s 
guns with relatively compact deflector-duct systems. 

4-7 RECOMMENDATIONS 

The modern high-pressure medium-caliber gun al¬ 
ready has great competition in the many weapons that 
have recently been developed, but it is assumed that 
the highly mobile gun and the multiple gun antiair¬ 
craft battery will continue to maintain their places in 
the midst of the new weapons. The survival of such 
guns will no doubt depend largely on the success with 
which their blast is brought under control. 

Investigations of blast effects and of the potentiali¬ 
ties of blast deflectors would be greatly aided if the 
scaling laws of blast phenomena were known. To de¬ 
termine these and at the same time augment our pres¬ 
ent knowledge of the emptying of guns, the following 
programs are recommended: 

1. The theoretical investigation of the interior bal¬ 
listics of a gun after shot ejection should be continued 
until a working method for determining the flux of 
momentum through the muzzle is derived. 

2. The systematic measurement of interior ballistic 
quantities should be continued. Records should be 
read for times after shot ejection at least as long as 
the time of travel of the projectile. This work should 
be done on small arms as well as on guns of large cali¬ 
ber and should include a range of caliber, tube lengths, 
relative powder loads, and rates of burning of powder. 

3. Work should be initiated for determining the 
distribution of momentum in the blast, that is, in 
transient jets of short duration. This problem pre¬ 
sents many difficulties but some solution should be 
attempted. 

4. A ballistic pendulum should be constructed capa¬ 
ble of carrying the larger of the medium-caliber guns. 
Such a pendulum would greatly facilitate investiga¬ 
tions of recoil problems. 

Field attachments comparable to the present muz¬ 
zle brakes will no doubt continue to be used for 
a long time. For instance, when a gun crew is ade¬ 
quately protected by armor plate and the gun fires at 
high elevations it might be possible to use a high-effi¬ 
ciency brake. It seems unlikely that small muzzle at¬ 
tachments that exhibit properties vastly different from 
those already observed can be constructed, but the fol¬ 
lowing programs would be profitable: 

5. Full-scale models of brakes similar to that de- 


CONI’11X TI \ L 






152 


MUZZLE BLAST 


scribed in Section 4.5 should be constructed with vari¬ 
ous reversal angles. It is believed that these brakes 
will tend to suppress flash. 

6. The effect on flash of simple multiple-baffle units 
should be investigated in various calibers. 

7. The feasibility of strengthening elevating mecha¬ 
nisms and balancing existing guns to take deflec¬ 
tors of larger capacity which give the blast greater 
upward deflection than those that have already been 
tested should be investigated. Deflectors similar to that 
shown in Figure 13 should be constructed to full scale. 

It seems quite certain that great reduction in blast 
effects cannot be achieved with anything less than 180- 


degree deflection of a large fraction of the blast, fol¬ 
lowed by the effective muffling of the deflected gas. 
It is still speculative to what extent blast can be con¬ 
trolled by such means. One final program is strongly 
recommended: 

8. A 180-degree deflector such as that described in 
Section 4.5 should be constructed in a caliber no 
smaller than 90 mm. Disposal systems should be in¬ 
vestigated which expand and cool the deflected gas 
before the eventual baffling and ejection to the point 
where burning and flash will not occur. If burning 
cannot be prevented within such a system by proper 
expansion, the effect of sprays should he investigated. 



PART III 


TERMINAL BALLISTICS 




Chapter 5 


FUNDAMENTALS OF TERMINAL BALLISTICS 


5.i INTRODUCTION 

he ability of a weapon to neutralize an objective 
depends, at least partly, on the relation between the 
amount of protection possessed by the target and the 
power of the weapon. Only the attacking missile and, 
within limits, its condition when it reaches the target, 
and the portion of the target that is attacked are un¬ 
der the control of the offense; the type, arrangement, 
and extent of the protection are at the disposal of the 
defense. This competition between the power of a 
given attack and the strength of passive protection 
supplies the subject matter of terminal ballistics. Spe¬ 
cifically, terminal ballistics is concerned with phe¬ 
nomena occurring at the target. Other divisions of the 
general subject of ballistics, interior and exterior, deal 
with the phenomena in the gun and the phenomena 
of free flight respectively. This subdivision of the sub¬ 
ject matter of ballistics into three parts is useful even 
though the distinctions are not always sharp or even 
applicable in all cases as, for example, with rockets or 
aerial bombs. 

52 the WORK OF DIVISION 2 IN 
TERMINAL BALLISTICS 

Different phases of terminal ballistics were studied 
by Division 2, NDRC, during World War II, the se¬ 
lection of problems and the emphasis placed on the 
various research programs being determined by prac¬ 
tical considerations arising from the needs of the 
Armed Services. These needs, of course, changed with 
the favorable progress of this war and the resulting 
general trend from defense to offense. 

Thus the terminal ballistics work of Division 2 was 
concentrated on certain selected problems rather than 
on an attempt to cover all of the unsolved problems 
in the field. In most cases the object of the research 
was basic information by which operational designs 
or procedures might be improved and made more ef¬ 
fective, rather than the development of a particular 
device or gadget. Correspondingly, the work was 
planned and organized primarily in terms of the tar¬ 
get material rather than according to the missiles con¬ 
sidered. Thus Chapters 6, 7, 8, and 9 describe work on 


different target materials. However, Chapters 10 and 
14, which are concerned with particular missile-target 
interactions and form part of the terminal-ballistics 
work of Division 2, did result in the design of a very 
special bullet for training aerial gunners and in the 
design of special methods of protecting tanks against 
shaped-charge missiles. 

Chapters 6, 7, 8, and 9 describe the terminal ballis¬ 
tics of steel, concrete, plastic protection, and earth 
from the point of view of the work done in Division 
2 during World War II. Much allied work from other 
sources is included in the text and references in order 
to give a connected picture without, of course, pre¬ 
tending to give a complete review of all outside work 
on the same general subject. After some early study of 
the terminal ballistics of ordinary and armor steels in 
general, the principal emphasis in the work on steels 
was placed on exploring the phenomena at high strik¬ 
ing velocities (Chapter 6). These studies furnish a 
factual basis for assaying future trends in the develop¬ 
ment of both arms and armor as well as suggesting 
some of the specific features of projectile design for 
hypervelocities. An extensive study of the terminal 
ballistics of concrete (Chapter 7) was initiated by the 
Committee on Passive Protection Against Bombing 
[CPPAB] (later the Committee on Fortification De¬ 
sign [CFD]) to obtain information on which a ra¬ 
tional design of protective structures, bomb shelters, 
and fortifications could be based. The information 
gained was also of value for the analysis of offensive 
operations. In this same connection, work was done 
on the terminal ballistics of earth and soils (Chapter 
8). Another research program, of particular interest 
to the Navy and Merchant Marine, dealt with deter¬ 
mining the kind and degree of protection afforded by 
plastic protection (British plastic armor) against 
small-arms fire (Chapter 9). Little or no work was 
done during World War II by Division 2 on the ter¬ 
minal ballistics of rock, stone, gravel, brick, wood, and 
other special materials which are of military interest 
in this field. 

It is the purpose of the present chapter to outline 
the scope of terminal ballistics and to discuss in a 
general way some of the principal phenomena and 
concepts involved. 



( 0\T! DKXTIAU 


155 






156 


FUNDAMENTALS OF TERMINAL BALLISTICS 


BULLETS Example: caliber ,30 


Example: caliber .50 


BALL 



gilding metal jacket 
lead alloy slug 


ARMOR 

PIERCING 


(AP) 



leod alloy filler 
carbon 
steel core 


BALL 


ARMOR 
PIERCING 

(AP) 



gilding metal jacket 
lead alloy filler 
mild steel core 


chrome molybdenum 
steel core 


PROJECTILES Example: 155 mm 

ARMOR PIERCING (AP) 

solid shot 



steel bode 
rotating band 
tracer cavity 


ARMOR PIERCING (AP) 

with windshield and bursting charge 



rotating bond 
base plug 
base plate 


windshield 
steel shell 
bursting charge 


BOMBS 



SHELL (high explosive) (HE) 


nose fuze 
bursting charge 
bourrelet 

Example: 1000 lb 



ARMOR* PIERCING CAPPED (APC) 


-base plate 


steel shell 


armor-piercing 
cap 

bursting charge 


GENERAL 

PURPOSE 


(GP) 


SEMI-ARMOR 

PIERCING 

(SAP) 


ARMOR 

PIERCING 

(AP) 



.'avaww 






auxiliary booster 
tail fuze 


Figure 1. Typical bullets, projectiles, and bombs. 


arming wire 
suspension lugs 
bomb case 


nose fuze 


bursting charge 
surrounds 

auxiliary boosters 


nose fuze plug 











































































































































































































IMPACT CONDITIONS 


157 


5.3 MISSILES 

Some of the conventional types of missiles are 
shown in Figure 1. Besides bullets, projectiles, and 
bombs, however, shaped-charge weapons, rockets, frag¬ 
ments, etc., may be considered missiles in a broad 
sense. 

5 31 Missile Properties 

The principal properties of a nondeforming projec¬ 
tile are its weight W, caliber D, and shape. If a pro¬ 
jectile deforms, these items change during penetration 
and are therefore not sharply defined. If only subsidiary 
parts of a projectile deform, such as windshield, cap, 
or jacket, reasonably good estimates of penetration 
can often be obtained by using only the weight, cali¬ 
ber, and shape of the nondeforming part of the pro¬ 
jectile. 

A derived projectile parameter which is particu¬ 
larly useful in comparing phenomena at different 
scales is the caliber density D, defined as liy^ 3 . This 
is a constant for similar projectiles of different cali¬ 
bers. For a given type of missile the value of D will 
remain within a narrow range for exterior ballistic 
reasons, i.e., in order to achieve satisfactory flight 
characteristics. This fact is an aid in estimating the 
weight of a hypothetical attacking missile of assumed 
caliber. Thus, both foreign and American armor¬ 
piercing [AP] bombs and conventional steel projec¬ 
tiles have caliber densities that usually lie in the 
interval 

D — 0.45 to 0.65 lb per cu in., 

with D — 0.55 lb per cu in. as a reasonably good aver¬ 
age value. For semi-armor-piercing [SAP] bombs the 
range is 

D = 0.20 to 0.35 lb per cu in., 

with D = 0.27 lb per cu in. as an average. The charts 
given in Figure 2 will facilitate estimates involving 
caliber density. 

5 3 2 Missile Deformation at Impact 

The missile depends for its action on the kinetic 
and chemical (explosive) energy it carries to the tar¬ 
get. Attention is restricted to the case in which the 
missile reaches the target mechanically intact since 
there are separate treatments of the remote effects of 
an explosive missile transmitted to the target by air 
blast, earth or water shock, and fragments. Further¬ 
more, the mechanical performance of the missile 


against the target before any explosion takes place 
stands in the forefront of our interest. 

At impact there is a competition between missile 
and target in which not only the target but also the 
missile may yield in varying degrees. Thus a steel pro¬ 
jectile may shatter against armor, and a general-pur¬ 
pose [GP] bomb or high-explosive [HE] shell may 
deform or rupture against concrete. In both cases a 
considerable indentation into the target may still be 
achieved, even though it is less than would be pro¬ 
duced by a nondeforming missile. Some of the typical 
features of Service missiles that are involved in the 
question of deformation or breakup may be seen in 
Figure 1. Thus, the function of an armor-piercing cap 
is to improve the terminal ballistic performance of a 
projectile against an armor target by inhibiting the 
breakup or shatter of the remainder of the missile. A 
windshield is added to the nose of some projectiles to 
improve their exterior ballistics; against targets like 
armor or concrete this windshield is crushed and swept 
away during the first stages of penetration. Interior 
ballistic considerations have resulted in the provision 
of a soft metal jacket on small-arms bullets to give the 
barrel a longer life when many rounds have to be 
fired; against steel armor or concrete these jackets are 
soon torn off even when the core remains intact. 

Except for some cases at high obliquity against thin 
plates, shatter or deformation handicaps a missile with 
respect to the target. The breakup of small-caliber AP 
cores in plastic protection was found to be an essential 
factor in the performance of the latter as a target. 
When fragments from an explosive shell or bomb are 
considered as individual missiles their target effect is 
greatly influenced by breakup; this is true to such an 
extent that it is difficult to devise experimental 
methods for recovering fragments intact for the pur¬ 
pose of assaying their original size, shape, and weight 
distributions as functions of direction from the shell 
or bomb. The extreme case of complete projectile shat¬ 
ter without sensible effect on the target was proposed 
and given a satisfactory practical solution in the fran¬ 
gible bullet for gunnery training (see Chapter 10). 

5.4 IMPACT CONDITIONS 

The principal impact conditions which need to be 
specified are striking velocity v 0 , the striking obliquity 
or angle of incidence 6, and the yaw. The last two are 
defined in Figure 3, together with several other terms 
relating to the geometry of impact. Bombs and pro- 


(/0XFI.DEXT1A6 








w/l= D IN LB/lN . 3 W/d = D IN LB/lN. : 


158 


FUNDAMENTALS OF TERMINAL BALLISTICS 


SMALL - CALIBER PROJECTILES 


fO 



MEDIUM - CALIBER PROJECTILES 



LARGE-CALIBER PROJECTILES 



AERIAL BOMBS 



Figure 2. Caliber density. 
































































































































































































































































































































































































































































































































































































































































































































































































































































































































































RESULTS OF IMPACT—PENETRATION AND PERFORATION 


159 


jectiles are designed to minimize yaw in flight, and it 
may be assumed in most terminal-ballistic problems 
that the yaw is zero unless otherwise observed or speci¬ 
fied. Increasing yaw tends to decrease the penetrating 

ANGLE OF YAW IS NOT 
NECESSARILY IN THE 
PLANE OF INCIDENCE 



ANGLE OF INCIDENCE, OR OBLIQUITY 


Figure 3. Geometry of impact. 


ability of a projectile or bomb and to increase its 
chances of deformation and breakup. 

The performance of a projectile against a given tar¬ 
get usually increases with striking velocity and de¬ 
creases with increasing obliquity. However, each of 
these factors also tends to increase the likelihood of 
projectile shatter, which can, in some cases, exactly 
reverse the expected trends. Thus a projectile that de¬ 
feats a plate at a certain striking velocity may shatter 
at a higher velocity and fail to defeat it. On the other 
hand, a projectile that ricochets intact at a certain 
obliquity may actually produce deeper indentations 
or even perforation at a greater obliquity if this causes 
shatter. 


without passing through it. The phrase “penetration 
into a massive target” or simply “massive penetra¬ 
tion” is often used when there is no bulging or rup¬ 
ture of material at the back face of the target, this 
being taken as evidence that the penetration in such 
cases does not depend on the finite thickness of the 
target. The term perforation is used specifically when 
the projectile passes completely through the target 
slab or plate. In the transition region between massive 
penetration and perforation the proximity of the back 
face of the target permits a greater penetration than 
would be obtained with a thicker target under the 
same conditions. In other words, in the transition re¬ 
gion the penetration is expected to depend on the tar¬ 
get thickness, while massive penetration is assumed 
not to depend on target thickness. 

In an idealized way Figure 4 shows the difference 
in the character of the perforation hole made by a 
nondeforming projectile in concrete and steel. With 
a brittle or frangible target, like concrete, both front 



5-5 RESULTS OF IMPACT — 

PENETRATION AND PERFORATION 


THIN CONCRETE TARGET STEEL TARGET 

Figure 4. Perforation of thin concrete target and of 
steel target. 


In considering the effects on the target it is useful 
to distinguish between penetration and perforation, 
particularly when the projectile remains in one piece 
and does not break up. With breakup of the missile 
some parts may pass through the target while others 
are stopped. In a strict sense the term penetration 
is reserved for the entry of a projectile into a target 


and back craters are formed; the material ejected 
from the front crater is called spall , while that from 
the back crater is called scab. With a tough or ductile 
target, like steel, the displacement of material from 
the path of the projectile usually results in the forma¬ 
tion of front and back petals rather than a separation 
of the material from the target as spall and scab. 






















Chapter 6 

TERMINAL BALLISTICS OF ARMOR 


6i INTRODUCTION 

erforation of steel has been studied more exten¬ 
sively than that of any other material, but until 
World War II few tests had been made with plates 
thicker than twice the caliber of the projectile. Up to 
that time there had been little interest in heavier plate 
since it could not be defeated with the Service weapons 
then available. As practical methods were developed 
for obtaining higher projectile velocities the situation 
changed. It then became necessary not only to extend 
investigations to thicker plate but to find better means 
of preventing projectile deformation. It is now pos¬ 
sible to perforate homogeneous armor almost 10 cali¬ 
bers thick, but the problem of armor perforation has 
by no means been completely solved. a > b > c 

611 Trend to Hypervelocities 

It has always been true that methods of defense 
have advanced to neutralize the destructive power of 
existing weapons. During World War II, for example, 
tanks were made less and less vulnerable by progres¬ 
sively increasing the amount and improving the ar¬ 
rangement of the protective armor. Before World War 
II, the principal antitank weapon of the United States 
was the 37-mm gun; at the end of the war a 90-mm 
gun firing a high-velocity, tungsten carbide cored pro¬ 
jectile was being used, and more effective weapons 
were being developed. 

Improvements not only in tank armor but in all 
types of passive protection may be expected to con¬ 
tinue and guns must likewise be made more effective 
to match these improvements. There are three con¬ 
ventional methods by which greater effectiveness can 
be obtained: 

1. As better methods of handling guns are devel¬ 
oped, their maneuverability is increased. This permits 
the replacement of small weapons by guns and pro¬ 
jectiles of larger caliber. 

2. By continued improvements in design, guns of 
all calibers can be made more powerful. 

3. The ability of any gun to perforate armor can 

a Pertinent to War Department Projects OD-75, CE-5, 
and CE-6; and to Navy Department Project NO-11. 

b See Chapter 5. 

0 See Weapon Data Sheets 2C3, 2C3a, 2C4, 2C5*, 2C5a, 
2C6, 2C7 of Chapter 19. 


usually be increased by the use of special projectiles 
of the subcaliber type. 

Merely increasing the size of a gun obviously offers 
only a partial solution to the problem; advances must 
come mainly from the development of more powerful 
guns and of better subcaliber projectiles. Advances 
along either of these lines involve the use of what 
are now termed hypervelocities, velocities in excess of 
3,000 fps. The practicality of projectile velocities in 
this range has already been well demonstrated; numer¬ 
ous gun and projectile combinations resulting in 
hyper velocities have been developed and certain of 
these have been successfully used in combat. Possi¬ 
bilities for substantial improvements have not been 
exhausted, however. 

612 Hypervelocity Projectiles 

in World War II 

The possibility of the practical use of hyperveloc¬ 
ities was well recognized before 1941, but suitable 
methods for obtaining these velocities had not been 
worked out. The idea of the tapered-bore gun 1 as well 
as the subcaliber projectile 2 for standard guns was 
not new, and efforts were continually being made to 
overcome gun erosion so that the power of conven¬ 
tional guns could be increased without unduly short¬ 
ening their life. 

Interest in unconventional methods of gun and 
projectile design was intensified in 1941 because of a 
report from the Libyan campaign in North Africa 
that the Germans were using a hvpervelocity, tapered- 
bore gun as an antitank weapon. Actually this gun 
was not extensively used, but it did lead to a mom¬ 
entary setback in morale and consequently provided 
a spur to programs for the development of hyperveloc¬ 
ity weapons in the United States, England, and Can¬ 
ada. Before the end of World War II all countries had 
successfully employed in combat high-velocity, tung¬ 
sten carbide cored projectiles which were provided for 
guns of various calibers. The principal Service type of 
the Americans, hypervelocity arm or-piercing [H YAP ], 
and of the Germans, armor-piercing [AP 40], was the 
composite rigid; that of the British, armor-piercing 
discarding sabot [APDS], was the discarding sabot. 
It is perhaps worth noting that none of these projec- 



160 


O 




INTRODUCTION 


tiles required modification of standard guns; the guns 
could therefore be used to fire alternatively projectiles 
of conventional and subcaliber types. The develop¬ 
ment of other methods had been brought to a success¬ 
ful conclusion but these methods were not widely used 
in the theaters of operation. 

In the United States the work in devising and de¬ 
veloping methods for obtaining hypervelocities was 
carried out by Division 1, NDRC, and the Army 
Ordnance Department. Additional studies of the ter¬ 
minal-ballistic aspect of the problem were made by 
Division 2, NDRC. 

The need for a program to investigate the terminal- 
ballistic phase had been emphasized by another re¬ 
port from the Libyan campaign. It appeared that 
guns firing 2-pounder AP shot were much less effec¬ 
tive at point-blank than at longer ranges. This appar¬ 
ently anomalous behavior resulted because at the high 
velocity near the muzzle the shot completely disinte¬ 
grated on impact, but at greater distances, having 
lost some of its velocity in flight, it remained intact. 3 
The reduction in penetrating ability due to breakup 
of the shot far offset any advantage that might have 
been expected because of its greater striking energy 
at the muzzle. Thus there was early recognition of 
the fact that a projectile might become less rather 
than more effective when its velocity is increased. 
The difficulty in designing a nondeforming projectile 
still remains one of the principal obstacles to the use 
of hypervelocity weapons. 

613 Studies of Armor Perforation 
in Division 2, NDRC 

Initial Hypervelocity Program 

When the hypervelocity program was first origi¬ 
nated in Division 2, NDRC, at the request of the 
Army Ordnance Department under project OD-75, 
it was described as an “investigation of the penetra¬ 
tion of homogeneous and face-hardened armor at 
striking velocities of 3,000 fps and above. Tests were 
to be made at t/d [thickness of plate/diameter of pro¬ 
jectile] ratios between 2 and 4 and at angles of obliquity 
ranging from 0 degree to the maximum within the 
capacity of the equipment. Plate hardnesses were to be 
such as to give Brinell readings of 250 or above.” 

Soon after work was begun, August 1942, it was 
recognized that the original directive was too limited. 
Actually, the tests were not restricted to plates less 
than 4 calibers thick nor were all firings conducted at 
velocities above 3,000 fps. The hypervelocity problem 


161 

is not so much one of determining projectile perform¬ 
ance in a particular range of velocities as it is of dis¬ 
covering the effect of increasing the velocity from 
low to high values. 

General Terminal-Ballistic Program 

Terminal-ballistic studies at high velocities repre¬ 
sented for Division 2, NDRC, a natural extension of 
earlier investigations using velocities that could be 
obtained with conventional guns and projectiles. In 
the earlier work, which was carried out for the U. S. 
Naval Ordnance Department under project NO-11 
and for the Corps of Engineers, IJ. S. Army, under 
projects CE-5 and CE-6, interest centered mainly in 
the properties of the plate and its ability to resist 
perforation. In the later work, the experimental range 
of velocities was extended from 3,000 to 5,500 fps 
and the emphasis was shifted from a study of plate 
behavior to considerations of projectile performance, 
particularly as it is affected by deformation. The pro¬ 
gram was originally planned and continued to be an 
empirical study of the general problem of projectile 
impacts against armor over the complete range of 
practical velocities. It was impossible, however, to 
consider all types of targets and to investigate all 
variables in projectile design. The tests were mainly 
limited to impact conditions likely to be encountered 
in combat and were not primarily intended to study 
basic physical phenomena. 

Purpose 

The purpose of the work was to test the feasibility 
of using hypervelocity projectiles to defeat armor pro¬ 
tection and to study the factors controlling perfora¬ 
tion. The ultimate goal was to obtain data that would 
indicate the impact conditions under which projectiles 
of different types would be most effective and would 
serve, at least in part, as a basis for projectile design. 

614 Scope of Present Report 

The discussion in the following sections is limited 
mainly to those aspects of the terminal-ballistic prob¬ 
lem covered by the work of Division 2, NDRC, but 
reference will be made to parallel work of other re¬ 
search groups. The report is not intended as a com¬ 
plete record of all contributions nor as a comprehen¬ 
sive review of all phases of the subject. For total cov¬ 
erage of tests relative to high-velocity impacts, refer¬ 
ence should be made to British and Canadian reports 4 
mentioned in the British Ordnance Board Proceed¬ 
ings, to papers by Frankford Arsenal, and to firing 


CONFIDENTIAL 







162 


TERMINAL BALLISTICS OF ARMOR 


records of the Aberdeen Proving Ground. Other or¬ 
ganizations in the United States that have made im¬ 
portant contributions to the general problem of armor 
perforation but have not been concerned with hyper¬ 
velocities are Watertown Arsenal, Naval Research 
Laboratories [NRL] and the Naval Proving Ground 
at Dahlgren. 

62 PROBLEM OF ARMOR PERFORATION 
BY INERT PROJECTILES 

Although a concise statement of the problem of 
armor perforation could be made, it would, through 
the omission of details, be misleading. Instead of a 
definition, a brief discussion will be given of the gen¬ 
eral problem. 

Neither the general problem of discovering the 
most efficient means of piercing armor nor the more 
specific problem of designing a projectile to perforate 
the maximum thickness of plate can be solved by 
terminal-ballistic considerations alone. The ability of 
ah armor-piercing projectile to defeat a particular 
target depends as much on the power and size of the 
gun and the range over which the projectile is fired 
as it does on the plate-projectile properties that con¬ 
trol perforation. Considering a given gun, the energy 
available from the powder is expended principally 
in overcoming frictional and engraving forces acting 
on the projectile during its travel through the gun, 
in heat transferred through the walls of the barrel, 
and in supplying kinetic energy to the powder gases 
and to the projectile.* 1 Part of the energy possessed 
by the projectile at the muzzle is lost to air resistance 
in flight, and only the remainder is available for pierc¬ 
ing armor. It is the province of interior ballistics to 
transfer as great a portion of the original energy into 
the muzzle energy of the projectile as possible, of ex¬ 
terior ballistics to reduce losses due to air resistance, 
and of terminal ballistics to use the remaining energy 
in the most effective way for perforating the target 
and producing subsequent damage. It is unfortunate 
that changes in projectile design desirable from a 
terminal-ballistic point of view may be detrimental to 
its interior and exterior ballistic behavior. 

A projectile can best use its striking kinetic energy 
for perforation if it remains entirely undeformed dur¬ 
ing impact. This basic idea is an almost intuitive con¬ 
cept which is confirmed by trials reported profusely 

d The energy of rotation of the projectile and recoil of 
the gun are usually neglected. 


throughout the literature. 3,5 Only one case is known 
to the writer in which this is apparently not true. 6 
in the attack of thin plate at very high angles of 
obliquity, a projectile of conventional nose shape may 
ricochet if it remains intact and require more energy 
for perforation than a projectile that shatters. Even 
under these exceptional conditions of attack, how¬ 
ever, it is likely that if a non deforming projectile of 
any nose shape were possible it could be designed to 
perforate with less energy than one that deformed. 7,30 
Although there is general acceptance of the idea that 
a projectile should be kept intact if possible, a feeling 
still persists in some quarters that this is of little 
importance for high striking velocities. This is im¬ 
plied in a well-known ordnance book, which states that 
“if very high striking velocities are obtained, penetra¬ 
tion is little affected by the material of which the 
projectile is composed.” It is conceivable that this 
might be true at sufficiently high velocities, but it is 
not true up to 5,000 fps, which is higher than the 
velocity of any present-day projectile in practical 
use. In general, the thickness of armor that can be 
defeated by a projectile with a given striking energy 
will fall between the limit thicknesses corresponding 
to the extreme cases of a nondeforming projectile on 
the one hand and a perfectly plastic projectile on the 
other. 

Although the nondeforming projectile represents 
the ideal, this cannot be attained in practice, at least 
not under all conditions of impact likely to be en¬ 
countered by projectiles fired from present-day guns. 
It is therefore necessary to accept some sacrifice, 
which usually appears through the addition of an 
armor-piercing cap. Although the projectile proper 
may be kept essentially intact by this means, there 
is still some loss in penetrating power due to the dis¬ 
integration of the cap itself. The cap will lead to im¬ 
proved performance only for conditions of impact at 
which the uncapped projectile deforms badly and the 
deformation greatly increases the energy required for 
perforation. To assess the feasibility of using a cap, 
one must know the performance of both the uncapped 
and capped projectile over a wide range of striking 
conditions. For the uncapped projectile it is necessary 
to determine (1) the energy required for perforation 
when no deformation occurs, (2) the conditions under 
which deformation takes place, and (3) the effect 
of the deformation in limiting perforation. For the 
capped projectile one must find the extent to which 
the above factors are affected by the addition of the 


■ I-MI)EjSTIA% 











PROBLEM OF ARMOR PERFORATION BY INERT PROJECTILES 


163 


protective material. All three factors are altered by 
changes in the projectile parameters. It is therefore 
convenient to resolve the investigation into separate 
studies of the individual variables, both as they affect 
the energy required for perforation directly when the 
projectile stays intact and indirectly through pro¬ 
jectile deformation. 

The parameters of a projectile are most easily speci¬ 
fied by giving first the projectile type (monobloc, 
capped, or jacketed). If the discarding pieces of a 
sabot are not considered, all practical projectiles fall 
into one of these three categories, which are pictured 
schematically in Figure 1. Both the capped and the 
jacketed projectiles are formed by adding protective 
material to the monobloc, so that the monobloc is not 
only the simplest type but is the basis of the other 
two. It is customary to consider first the performance 
of the monobloc and then to determine the effect of 
the cap or jacket in modifying its behavior. 

As far as its performance as an undeformed pro¬ 
jectile is concerned, the monobloc is completely spec¬ 
ified if its size and shape are uniquely defined and 
its density given. The size is given by stating the 
diameter (or caliber) of the projectile; the quantities 
defining the shape are then made independent of size 
by expressing them as multiples of the diameter (i.e., 
in calibers). Classification according to shape is con¬ 
ventionally made by considering the body and the 
nose separately. Since the body is usually in the form 
of a circular cylinder with a square base, it can be 
specified, except for details, by one quantity, the cal¬ 
iber length. A variety of nose shapes (tangent ogival, 
secant ogival, conical, double-radius ogival, and com¬ 
bination of tangent ogive and cone) have been used; 
one of the most common is the tangent ogive shown 
in Figure 1. From the size and shape parameters and 
the density one can determine, either by direct in¬ 
tegration or by methods developed for rapid numerical 
calculation, 8 the mass, volume, center of gravity, and 
moments of inertia. Mass and density are not inde¬ 
pendent ; in practice it is usual to give the mass. Thus 
when the projectile can be taken as a rigid body the 
variables commonly considered are mass, diameter, 
nose shape, and total projectile length. 

If the projectile deforms, the strength of the mate¬ 
rial must also be taken into account. A complete in¬ 
vestigation of this factor would include not only 
terminal-ballistic tests relative to the occurrence, 
causes, and effects of deformations resulting from 
changes in the projectile’s strength, but also studies 
leading to the development of higher strength mate¬ 


rials. The latter aspect of the problem is as important 
as the first, but its solution is essentially the respon¬ 
sibility of ferrous and powder metallurgists rather 
than that of ballisticians. This phase of the subject 
will not be treated in the present report. Discussion 
will be confined to questions concerning the depen- 



MONOBLOC PROJECTILE 



CAPPED PROJECTILE 



JACKETED PROJECTILE 


Figure 1 . Idealized projectile types. 

deuce of performance on such quantities as projectile 
hardness and bend (transverse rupture) strength. 

No completely satisfactory system for specifying 
caps and jackets has been devised, but just as with the 
core their effectiveness must depend, at least to some 
extent, on the mass, size, shape, and strength of the 
protective material. 

The effect of changes in the projectile parameters 
discussed above usually depends on the hardness, 
thickness, and arrangement of the plates making up 
the target. Whether the principal emphasis falls on 
the projectile or on the target depends on whether 
the interest is in offense or defense. 

In summary, the terminal-ballistic problem of 
armor perforation is essentially one of determining 


CONFIDENTIAL 



























164 


TERMINAL BALLISTICS OF ARMOR 


how the energy required to defeat a steel target de¬ 
pends on the mass, size, shape, and mechanical 
strength of the projectile components as well as the 
hardness, thickness, and arrangement of the plates 
composing the target. The problem is complicated not 
only by the large number of variables involved but by 
the likely occurrence of projectile deformation. The 
solution to the problem, which can be obtained only in 
a practical sense, must be combined with solutions 
to the problems of exterior and interior ballistics be¬ 
fore answers are possible to more general questions 
such as how to design a projectile to perforate the 
maximum thickness of plate, or what is the most effi¬ 
cient gun-projectile combination to neutralize a given 
objective. Actually no completely rational system of 
projectile design has been devised, but there is avail¬ 
able a great deal of qualitative and semi-qualitative 
information on the effect of changes in various para¬ 
meters. 

63 EXPERIMENTAL TECHNIQUES FOR 
TERMINAL-BALLISTIC STUDIES 

In problems concerned only with the perforation 
of armor the quantity of most direct practical interest 
is the energy absorbed by the plate. Logically, how¬ 
ever, terminal-ballistic studies should begin with a 
measurement of the forces resisting the bullet during 
penetration. Until the nature of these forces, which 
is only partially understood at present, is completely 
known it seems unlikely that an exact theory of pro¬ 
jectile penetration will be developed. Furthermore, a 
knowledge of force and time is needed for problems 
in fuze design and for determining the stresses in a 
projectile leading to its deformation. Only average 
forces can be calculated from the total energy absorbed 
unless assumptions are made concerning the mecha¬ 
nism of penetration. 

Unfortunately it is experimentally very difficult to 
determine the forces of the plate-projectile interac¬ 
tion because of the extremely short time of impact. 
Only a few attempts at direct measurement have been 
made and these were all carried out for normal in¬ 
cidence of the projectile. For studying impacts against 
steel an optical method has been developed by which 
a shadow of the base of a penetrating projectile is 
recorded on a rotating drum camera. 9,10 By a suit¬ 
able analysis the position, velocity, and deceleration 
of the projectile may be deduced as functions of time 
from the photographic record. A second method 11 of 


measuring deceleration during impact should be men¬ 
tioned, although it can be used only with nonmagnetic 
and nonconducting target materials like concrete. 
(See also Section 7.7 of Chapter 7.) The method con¬ 
sists in magnetizing the projectile and recording the 
electromotive force induced in two suitably placed 
coils by means of a cathode-ray oscillograph [CRO]. 
The target is placed between the two coils in a region 
where the induced electromotive force is dependent 
only on the velocity of the bullet and not on its posi¬ 
tion. With a linear sweep for measuring time, the 
trace on the oscillograph is a line, each point of which 
is displaced a vertical distance proportional to the 
velocity. The deceleration is obviously obtained as a 
function of time by measuring the slope of the line 
at various points. 

The present report deals mainly with the total en¬ 
ergy absorbed by the plate. This quantity is deter¬ 
mined from a knowledge of the projectile’s striking 
energy and the energy it retains after perforation, 
that is, the residual energy. Of particular interest is 
the energy absorbed wdien the plate just succeeds in 
stopping the projectile. If the striking energy is above 
this limiting value, the projectile will usually per¬ 
forate ; if it is below, it will fail. Sometimes, however, 
the projectile fails at the higher energy and succeeds 
at the lower. 

The limit energy is conventionally measured either 
by “bracketing” or by the method of residual veloc¬ 
ities. To determine a bracket, firings are conducted by 
varying the projectile’s striking velocity until shots 
are obtained close to, but on either side of, the limit; 
the limit energy is then calculated from the average 
value of the bracketing velocities and the projectile’s 
mass. The method of residual velocities 12 is more ele¬ 
gant but, because of practical difficulties, is restricted 
mainly to normal attack by nondeforming projectiles. 
In this method several projectiles are fired at differ¬ 
ent velocities above the limit and the striking and 
residual velocities measured for each shot. If the resid¬ 
ual energies are plotted as a function of the strik¬ 
ing energies, the points representing the different 
shots fall on a straight line and extrapolation of this 
line to the striking energy axis gives the limit energy. 

In the conventional terminal-ballistic range the 
equipment consists of guns for propelling the projec¬ 
tiles to the target, means for supporting and orienting 
the plate, apparatus for measuring striking and resid¬ 
ual velocities, and auxiliary devices such as micro- 
flash and spark units for observing the projectile be- 


■ i'M- i"l N I i A U 








EXPERIMENTAL TECHNIQUES FOR TERMINAL-BALLISTICS STUDIES 


165 


fore, during, and after perforation. Each investigator 
naturally has his own techniques; only those used by 
Division 2, NDRC, will be described. 

63,1 Projectile Propulsion 

For studying the effect of impacts, any method of 
firing is satisfactory provided the projectile arrives 
at the target in good condition, without yaw and with 
sufficient velocity. Ease in performing and preparing 
for a test is often the principal consideration in 
choosing between possible methods. 

The use of a smoothbore gun was suggested by the 
need for firing simple projectiles. Actually the manu¬ 
facture of projectiles consumes a great deal more time, 
effort, and money than the carrying out of a plating- 
trial. Thus any simplification in the design of a pro¬ 
jectile which does not affect its perforating ability 
represents a tremendous saving. Aside from this sav¬ 
ing, simplification is at times necessary; for example, 
in studying the effect of jackets, unjacketed projec¬ 
tiles must be fired for comparison. The smoothbore 
gun does not require the use of a rotating band or 
jacket and makes the problem of cap attachment much 
simpler since the cap is not subjected to centrifugal 
forces. Lack of rotation has been shown 13 to have a 
negligible effect on the projectile’s perforating ability. 

Such a gun has been successfully used for work at 
model scale 14 (.244 caliber) over a four-year period. 
Yaw is avoided by placing the muzzle of the gun 
within 6 in. of the target, which is mounted on a 
ballistic pendulum to allow measurement of the strik¬ 
ing velocity. Since blast from the gun would affect 
the pendulum, the projectiles are fired through a piece 
of rubber covering a hole in a metal blast shield. By 
using an oversized chamber and' long barrel, unjack¬ 
eted tungsten carbide projectiles, having a caliber 
density about twice that of conventional steel projec¬ 
tiles, have been fired at velocities up to 3,850 fps. 

In order to attain higher velocities and to work 
with larger calibers, composite rigid and sabot pro¬ 
jectiles have been used in standard guns. Tapered- 
bore guns or guns with tapered muzzle attachments 
are not only complicated in themselves but require 
jacketed projectiles that are difficult to manufacture. 
The composite rigid is usually the easiest hyperveloc¬ 
ity type to make but often cannot be used because of 
the jacket. Any type of subprojectile (monobloc, 
capped, or jacketed) can be used with a sabot. Much 
simpler sabots can be used for terminal-ballistic tests 
than are required for combat since extreme accuracy 


is not important and yaw can be reduced at the target 
by setting the gun at a minimum yaw distance. The 
principles of sabot design are given in a report 15 by 
the Division 1, NDRC group at the University of 
New Mexico. 

6 3 2 Plate Suspension 

Test has shown 10 that the method of plate support 
is of secondary importance in controlling the energy 
required for perforation. Thus, in the extreme case 
of a rigid support on the one hand and perfectly free 
suspension on the other, a free plate weighing only 
six times as much as the bullet required 9 per cent 
more energy for perforation. It is probable that the 
difference would be less for plates of reasonable size. 
The lateral dimensions of the plate are likewise not 
of prime importance provided the extent is sufficient 
to include the principal region of plastic deformation. 
The insensitiveness of these factors implies that 

(1) no form of springs, cushions, or nets can add 
substantially to the stopping power of a target and, 

(2) except in terminal-ballistic tests requiring high 
absolute accuracy, variations due to differences in the 
type of support or the extent of the plate need be 
of no concern if the lateral dimensions are at least 
25 calibers. Actually, tests are often performed with 
plates smaller than this and it is likely that little 
error is introduced by so doing, but definitive experi¬ 
ments covering this point are lacking so this remains 
a moot question. 



Figure 2. Plate support for terminal-ballistic tests. 


CO \ I lOK.Vri AL ; 
































166 


TERMINAL BALLISTICS OF ARMOR 


One type of plate support that has proved conven¬ 
ient for plates weighing up to 1 ton is shown sche¬ 
matically in Figure 2. The plate can be shifted either 
laterally or vertically and turned so as to allow any 
angle of attack. Several shots can easily be taken on 
the same plate without shifting the position of the 
gun. In order to determine the angle of incidence a 
protractor is magnetically attached at the expected 
point of impact before each shot. The protractor is 
set by adjusting an index arm so that it is in line 
with the muzzle of the gun as seen in a mirror which 
is parallel to the face of the plate. 

6,3,3 Velocity Measurements 

The principal criterion for the goodness of velocity 
measuring equipment is the attainment of accurate 
determinations at the target. In order to avoid the 
vagaries involved and the time consumed in making 
corrections for velocity lost in flight, the equipment 
should measure as nearly as possible instantaneous 
values rather than average values over long base lines. 
Measurement of instantaneous values, or their ap¬ 
proximate determination by means of a short base line, 
has the further advantage that higher striking veloc¬ 
ities can be obtained because the gun can be fired 
at short range; this is particularly important when 
light windshields are omitted to simplify the pro¬ 
jectiles. 

Measurement of both striking and residual veloc¬ 
ities can be made for normal impact by means of a 
double ballistic pendulum. 14,17 A transmission pen¬ 
dulum supports the target, and a terminal pendulum 
stops the projectile after perforation. For the pendu¬ 
lums described in the reference, the overall probable 
error in a velocity measurement made with the trans¬ 
mission pendulum is 0.10 per cent and with the 
terminal pendulum is 0.06 per cent. These are prob¬ 
able errors of the apparatus only and do not include 
errors in the results due to inhomogeneity of the steel 
plates, spalling of the plates, etc. 

A second instrument, 18,19 which also fulfills the 
requirement of being able to determine an essentially 
instantaneous velocity with good accuracy, measures 
the time of passage of a projectile over a very short 
(1 to 4 ft) known distance. The base line is defined 
by two light beams, each of which consists of a nar¬ 
row sheet covering an area of about 1 sq ft. As the 
beams are successively interrupted by the projectile, 
electric pulses are generated by phototubes and trans¬ 
mitted to a spiral chronograph which measures the 



Figure 3 . View of light beams and photocells for 
measurement of projectile velocities. 


time between their reception. Figure 3 shows the 
physical arrangement of the light beams and photo¬ 
cells. When the light beams are placed close to the 
target the quantity measured can usually be taken 
as the striking velocity without correction. A deter¬ 
mination of the velocity can be made within 30 sec 
after the shot with an accuracy of better than 0.4 per 
cent. The principal limitations of the light beams and 
photocells are that they do not operate reliably with 
projectiles traveling at speeds near the speed of 
sound, and they cannot be successfully used for mea¬ 
suring residual velocities. 

The heart of the above equipment is the spiral 
chronograph which was developed to measure time 
intervals of a few msec to an accuracy of better than 
1 ix sec. During the lapse of time between the two 
pulses a spiral is traced out on a cathode-ray tube at 
a constant known angular velocity; the spiral trace 
starts with the first pulse and stops with the second, 
so that the number of revolutions appearing on the 
cathode-rav tube screen is a direct measure of the time 
interval. A picture of one of the spirals with blank¬ 
ing spots at 5-fx sec intervals is shown in Figure 4. 
A long persistent screen is used on the chronograph 
so that a visual reading of the spiral is obtained as 
well as a photograph. 


t 'i >N I I1 >K.\ I I VI* 





















DEPENDENCE OF STRIKING ENERGY ON PROJECTILE PARAMETERS 


167 



Figure 4. Photograph of spiral chronograph trace. 


Since light beams and photocells cannot be success¬ 
fully used for measuring projectile velocities behind 
the plate, special equipment has been developed for 
this purpose. The method involves taking spark shad¬ 
owgraphs of the projectile at two successive positions 
along its path. From these pictures and the geometry 
of the optical system, it is possible to find the distance 
traveled by the projectile between exposures. To de¬ 
termine the time between exposures and thus the 
residual velocity, light from the two sparks used to 
produce the shadowgraphs is allowed to fall on photo¬ 
tubes which actuate the spiral chronograph. This ap¬ 
paratus has the advantage that in addition to measur¬ 
ing the residual velocity it furnishes a record of the 
condition of the projectile immediately after perfora¬ 
tion of the plate. Although the base line is variable 
it is never over 2 ft. The accuracv of measurement is 
comparable to that obtained with the light beams and 
phototubes, but the time required for making a deter¬ 
mination is considerably longer. 

634 Auxiliary Apparatus 

It is often useful to know the condition of the pro¬ 
jectile before and during impact as well as after per¬ 
foration. For this purpose spark shadowgraphs and 
microflash photographs are used. Examples of such 
pictures are shown in Figures 6 and 9. In this con¬ 
nection mention should be made of the multiple-spark 
apparatus 20,21 developed in England under the aus¬ 
pices of the Armament Research Department [ARD]. 


With this equipment, which is based on the optical 
method of Schardin and Cranz, a series of spark pic¬ 
tures is taken showing the projectile at successive 
intervals during its penetration cycle. Since times 
between exposures are measured, the striking velocity, 
residual velocity, and an estimate of the deceleration 
at different stages of penetration can be obtained. 


6-4 DEPENDENCE OF STRIKING ENERGY 
ON EXTERIOR AND INTERIOR 
BALLISTIC BEHAVIOR 

Several attempts have been made 2,6,22 at calculating 
the size of core for a subcaliber projectile that will lead 
to perforation of the greatest single thickness of homo¬ 
geneous armor. This problem is similar to that of find¬ 
ing the best length of projectile or the best density of 
material. In these problems changes always occur in 
the mass and sometimes in size of the projectile com¬ 
ponents and as a result there are variations in the 
projectile’s striking kinetic energy as well as in the 
absorption of this energy by the plate. Tlius the max¬ 
imum energy that can be obtained at the muzzle of 
a given gun depends on the total mass of the projectile 
and, if a sabot type is being considered, the fraction 
of the total muzzle energy not wasted in the carrier 
varies with the relative masses of the subprojectile 
and the discarding pieces. Of the energy possessed by 
the subprojectile, a certain portion will be lost in 
flight, and the mass and size of the subprojectile are 
factors controlling the extent of this loss. 

The difficulty in calculating how the relative dis¬ 
tribution of energy changes with variations in the size 
and mass of the projectile components lies in the fact 
that the ballistic behavior cannot be exactly described 
by simple analytical expressions. Although tables and 
graphs are routinely used 23,24,25 to compute the per¬ 
formance of particular projectiles, these will not be 
employed in the present discussion. Approximate ex¬ 
pressions will suffice for purposes of illustration, but 
it is not proposed that these be used for purposes of 
exact design. 

641 Muzzle Energy of Subprojectile 

An increase in muzzle velocity can always be ob¬ 
tained with a given bore and chamber by decreasing 
the mass of the projectile and employing a quicker 
burning powder. The following relation gives an esti¬ 
mate of the total muzzle energy that can be supplied 


< ;< i S U i I >K.\ T1 AXj 









168 


TERMINAL BALLISTICS OF ARMOR 


to a projectile of mass M without exceeding the safe 
maximum pressure of the gun: 


1 C 

1 + 3M ] = 


1 + 1 ° 


31, 


( 1 ) 


where ep is the muzzle energy of a standard full-caliber 
projectile of mass Mp and C is the powder load. The 
muzzle energy e s of the subcaliber projectile is given 

by 


e 


s 




where M s is the mass of the subprojectile. If the sub¬ 
caliber projectile varies only in size, its “caliber den¬ 
sity” will remain constant and consequently 



f, 



where 7? [= cl s /d F ] is the ratio of the diameter of the 
subprojectile to that of the gun. This assumes that all 
projectiles have the same shape as a given prototype. 

The total mass of the projectile M depends on the 
type of carrier used; for a particular type, the mass of 
the carrier M c (R) will vary in a definite way with the 
ratio E. Thus, 

M = M a +M£R) = M f U 3 + M C (R). (4) 

By combining equations (1), (2), (3), and (4), 
the ratio of the muzzle energy of the subprojectiie to 
that of the standard full-caliber projectile can be de¬ 


termined for a given gun in terms of the ratio R. This 
energy ratio will be designated 17(0), where the zero 
in parentheses is intended to imply that the value is 
for point-blank range. Thus, 

E(0)= e f- (5) 

This is a definite function of R for a given gun and 
projectile type. Values of 17(0) are given in Table 1 
for R values ranging from 1 to 0.54. The gun in this 
case is the 37-mm M3, the projectiles are scale models 
of a particular steel projectile, 0 and all values are 
relative to the performance of a full-caliber 1.95-lb 
projectile having a muzzle energy equal to that of the 
37-mm M51. It will be noted that the velocity is also 
directly related to R , increasing as R decreases. 

As one would expect, the velocity of the subpro¬ 
jectile increases but its kinetic energy decreases as 
its diameter becomes smaller. If the caliber density 
of the prototype were increased, not only would the 
muzzle energy of the complete projectile be increased 
for subcaliber projectiles of all sizes [equation (1)], 
but a greater fraction of this energy would reside in 
the subprojectile [equation (2)]. e The mass could be 
increased either by using for the core a denser mate¬ 
rial, such as tungsten carbide, or by increasing the 
length of the projectile. 

e It is usually not necessary to increase the weight of the 
carrier in direct proportion to the increase in the mass of the 
subprojectile. 


Table 1. 


Performance of subcaliber steel projectiles as a function of core diameter. 


Diameter 

ratio 

R 

Muzzle 

velocity 

To 

(fps) 

Range (yd) 

0 

1,000 

9 

‘■‘l 

000 

E( 0) 

T( 0) 

E (1,000) 

T( 1,000) 

£(2,000) 

T(2,000) 

(37-mm) 








1.00 

2,851 

1.00 

1.00 

1.00 

1.00 

1.00 

1.00 

0.90 

3,216 

0.93 

1.09 

0.93 

1.09 

0.93 

1.09 

0.80 

3,637 

0.83 

1.18 

0.82 

1.16 

0.81 

1.15 

0.70 

4,112 

0.71 

1.25 

0.69 

1.22 

0.67 

1.19 

0.60 

4,628 

0.57 

1.30 

0.53 

1.22 

0.49 

1.15 

(20-mm) 








0.54 

4,946 

0.47 

1.29 

0.43 

1.20 

0.38 

1.09 


R = 
E(x) = 
T(x) = 


subprojectile diameter 
gun diameter. 

energy of subprojectile at range x 

energy of similar full-caliber projectile at range x. 

limit plate thickness of subprojectile at range x 

limit plate thickness of similar full-caliber projectile at range x 


tA'M- il’I'N n \h 










































DEPENDENCE OF STRIKING ENERGY ON PROJECTILE PARAMETERS 


169 


642 Energy Loss Due to Air Resistance 


In many cases a hypervelocity projectile loses en¬ 
ergy in flight at a greater rate than do projectiles 
fired at lower velocities. As a result, the hypervelocity 
projectile may perforate more armor at the muzzle 
but lose this advantage if fired over a long range. 
This has happened so often in practice that it is some¬ 
times felt that a hypervelocity projectile is necessarily 
a short-range projectile and that its ineffectiveness 
at long ranges is due to the high velocity at which 
it is fired. Actually an increase in velocity is in itself 
an advantage; the poor performance that has been 
observed has always resulted because the hyperveloc¬ 
ities were attained by using projectiles having low 
ballistic coefficients. 

For air of standard density the fractional loss in 
energy for a projectile traveling a distance dx is 
given by: 


de(x) 

e(x) 




where e(x) is the energy of the projectile at range x, 
K is the “drag coefficient,” 

C[ =M/id 2 ] is the ballistic coefficient for a 
projectile of mass fl/, diameter d, and 
form factor i. 

Thus, if the drag coefficient K were independent of 
the velocity, the fractional rate of change of energy 
with distance would also be independent of velocity. 
Actually, however, for velocities above the velocity of 
sound, K decreases as V increases so that the frac¬ 
tional energy loss is less the higher the velocity. In 
other words, if the power of a gun is increased not only 
will the muzzle energy of the projectile be greater but 
there will be a smaller fractional loss in energy over a 
given range. 

To determine the magnitude of this effect the vari¬ 
ation of K with velocity must be known. For projec¬ 
tiles with a Yio secant ogive (G- s Siacci table), K 
can be represented fairly well by k( I 72 )— 3/8 in the ve¬ 
locity range between 2,000 and 4,500 fps. Substituting 
into equation (6) and integrating yields 

*■(*) = (1 - 4 * )W ’ (7) 

where F(x) is the fractional energy retained at range 
x (ft), and 

fc' 

5 " cv}’ 

k ' is a constant, C the ballistic coefficient, and V 0 the 
muzzle velocity. 


An increase in either the muzzle velocity or the bal¬ 
listic coefficient results in an increase in the energy 
retained at a given range. For a subcaliber projectile, 
C decreases in direct proportion to R ; f if the muzzle 
energy of the subprojectile were constant and thus in¬ 
dependent of R, the increase in V 0 would slightly 
more than balance the decrease in C, but since the 
muzzle energy decreases with decrease in R, the value 
oiF(x) is somewhat less for a sub- than a full-caliber 
projectile. 

By expressing E(x), the ratio of the striking en¬ 
ergies of the sub- and full-caliber projectiles at range 
x, in terms of the fractional energy retained by each 
projectile 


E(x) 


e s(U 

e F (x) 


« a (0) F _sW 
e F (°) F f (x) 




Values of E(x) are given as a function of R in Table 
1 for 1,000- and 2,000-yd ranges, together with the 
values of E( 0) that were discussed in the previous 
section. 

It will be noted that the ratio of the striking kinetic 
energy of a subcaliber projectile to that of the full- 
caliber projectile decreases with increase in range, and 
that the rate of decrease is greater the smaller the sub¬ 
projectile. For example, with R equal to 0.7, the values 
of E( 0), ^(1,000), F(2,000) are 0.71, 0.69, 0.67 re¬ 
spectively, while with R equal to 0.54 they are 0.47, 
0.43, 0.38. Thus if hypervelocities are obtained by us¬ 
ing a subcaliber projectile, the performance relative to 
that of a similar full-caliber projectile is likely to de¬ 
teriorate with range. This does not mean, of course, 
that the range performance of a tungsten carbide 
cored subprojectile will necessarily be worse than that 
of a full-caliber steel projectile; in fact it will usually 
be better, because the mass, and therefore the ballistic 
coefficient, of the subprojectile will be increased by 
using tungsten carbide. Any increase in the mass of 
the prototype, either by an increase in density or in 
length, will lead to a larger value of F(x), which 
means smaller energy losses in flight. 


643 Stability 

The necessity of maintaining stability is one of the 
factors setting a lower limit to the diameter of a sub¬ 
projectile or an upper limit to its length. At the muz- 
- * 

f From equation (3) and the definition for the ballistic co¬ 
efficient M M f R n 

c = id*~ ~ Cf ’ 

where a constant C F is the ballistic coefficient for the full-cali¬ 
ber projectile having a diameter equal to the gun diameter d g . 














170 


TERMINAL BALLISTICS OF ARMOR 


zle of a fixed gun the stability factor S of a subcaliber 
projectile is given by 

8 =****, (9) 

X M P„n 2 £„ 

where p = average projectile density (strictly, the 
equation applies only to projectiles of uni¬ 
form density), 

A 0 = dimensionless coefficient proportional to 
moment of inertia about projectile axis 
[A = t rpd 5 A 0 ], 

B 0 — dimensionless coefficient proportional to 
moment of inertia through center of grav¬ 
ity and perpendicular to projectile axis 
[B = 7t p d^B q ], 

Km — overturning moment coefficient, 
p a — density of air, 

n = distance along barrel per turn of rifling 
measured in calibers of gun. 

As indicated by this equation, S decreases with de¬ 
crease in R. g Due to changes in A 0 , B 0 , and K M , S 
also varies with projectile length, decreasing rapidly 
as the projectile is made longer. Thus, if the projectile 
is to be stable, that is, if 8 is to have a value at least 
equal to 1, there is a maximum projectile length for 
each value of R ; as R becomes smaller the maximum 
length expressed in calibers likewise decreases and it 
would appear that the caliber length must necessar¬ 
ily be less for sub- than full-caliber projectiles. This 
problem is complicated, however, by terminal-ballistic 
considerations. The tendency of a projectile to break 
on impact increases with its length and this breakage 
may degrade its perforating ability. It appears that in 
many guns the twist of the rifling is sufficiently large 
that the length of a full-caliber projectile is limited 
by projectile breakage rather than stability. For these 
guns the full-caliber projectile can be scaled down 
without producing instability; S then plays the role 
of a limiting factor for determining the smallest value 
of R that can be used. Only for values of R less than 
this is the stability factor important for determining 
the length of the projectile. 

Although it appears from equation (9) that the 
stability factor increases with an increase in the den¬ 
sity of the material, which would provide a further 
reason for using tungsten carbide, this equation ap- 

g The stability factor does not decrease quite so rapidly 
as R 2 , because for supersonic velocities K M , like the drag 
coefficient, decreases as the velocity increases. The velocity 
that can be obtained with a given gun increases with a de¬ 
crease in R , so K m likewise decreases slightly. 


plies strictly only to monobloc projectiles. For jack¬ 
eted projectiles the core must be kept well forward to 
gain full advantage of the heavier material. 

6AA Striking Energy 

The greatest striking energy can be obtained from 
a given gun by using a full-caliber projectile made 
from the most dense material possible and having the 
greatest length consistent with the maintenance of 
stability. The advantage of the sub- over the full-cali¬ 
ber projectile for perforating thicker armor results 
solely from its terminal-ballistic performance which 
must be considered in the determination of an opti¬ 
mum size. It is also clear that terminal-ballistic re¬ 
sults should be considered in deciding upon the best 
projectile length. 

*5 STEEL AS A PROTECTIVE MATERIAL 

Section 6.4 deals with the dependence of striking 
energy on the principal projectile parameters. There 
remains the problem of determining the energy re¬ 
quired for plate perforation as a function of both the 
plate and projectile properties. The present section is 
concerned with the relative effectiveness of armor pro¬ 
tection and with the limit energy for a nondeforming 
projectile. Except for the effect of changes in projec¬ 
tile size and weight, this section deals only with the 
properties of the plate. 

651 Effectiveness of Armor Protection 

Comparison with good quality reinforced concrete, 
which for economic reasons is the usual basic mate¬ 
rial in fixed fortifications, furnishes an idea of the 
relative effectiveness of steel as a protective material. 
To afford equal protection against nondeforming pro¬ 
jectiles of small and intermediate calibers, homogene¬ 
ous armor need be only about one-sixth as thick as 
concrete. The armor has the added advantage that, 
due to its hardness, it is more likely to deform or shat- 
ter the projectile and thus further reduce its perfora¬ 
ting ability. Furthermore, spalling and cracking are 
not as likely with good quality armor as with concrete, 
so that it is better able to withstand repeated attack. 
Even though antitank guns were greatly improved 
after 1940, it was still possible in 1945 to build highly 
maneuverable armored tanks that were immune to 
frontal attack except at very short range. 

The type of armor protection most commonly used 
consists of a single plate of homogeneous armor and 


( uNJ-J DEXT1AL 








STEEL AS A PROTECTIVE MATERIAL 


171 


the present report deals mainly with this type of tar¬ 
get. Face-hardened armor is appreciably better than 
homogeneous only if the hard surface succeeds in shat¬ 
tering the projectile. Shatter can often be prevented 
by the use of an armor-piercing cap and when the cap 
accomplishes its purpose the advantage of face-hard¬ 
ened armor largely disappears. At the end of World 
War II, the face-hardening process was rarely being 
used except for heavy plates in naval construction. It 
might be profitably used in small sizes, however, if it 
were protected by a thin, spaced plate for cap removal. 


6.5.2 Perforation Energy—Mechanisms of 

Plate Failure 

If the energy required for perforation by projectiles 
of a given shape depends only on the size of the pro¬ 
jectile, the strength and thickness of the plate, and 
the angle of attack, a dimensional analysis indicates 
that the perforation formula must have the form 


ei 

d 3 



WT 2 

or-- 

d 3 



C = 2gC, (10) 


where ei (limit energy) = minimum energy re¬ 
quired for perforation, 

W = projectile weight, 

Yi = limit velocity, 11 
d = maximum projectile diameter, 
t = plate thickness, 

C = measure of strength of plate material ex¬ 
pressed as force per unit area, 
g = acceleration due to gravity, 
f(t/d,6)= general function of t/d and 0 , 

0 — angle of incidence. 

Although there are indications that this equation is 
not exactly correct, it is sufficiently true to provide a 
simple basis for correlating experimental data. Thus, 
in Division 2, NDRC, Data Sheet 2C3 of Chapter 19, 
the results of proof firing of monobloc projectiles of 
various sizes against homogeneous armor are repre¬ 
sented by plotting the specific limit energy WV^/d 3 
against the plate thickness expressed in calibers t/d. 
The measured values fall within a narrow band for 
each angle of attack; the spread of the bands is due 

h Two limit velocities are in common use: (1) minimum 
striking velocity required for complete perforation with zero 
remaining velocity [“Navy limit” (U.S.) and “critical velocity 
or W/R limit” (British)]; (2) minimum striking velocity re¬ 
quired to produce a hole through which light can be seen, the 
projectile being removed if necessary [“Army limit” (U.S.) 
and “ballistic limit” (British)]. Unless otherwise specified, the 
“Navy limit” will be used in this report. 


mainly to scatter in the data and only in small part to 
failure of equation (10). 

The form of the function f(t/d,6) depends on the 
mechanism of plate failure. Ideally a failure may be 
classified as either a plugging or a ductile type, but 
cases sometimes occur in practice that combine the 
elements of both. 

Plugging Failure 

When complete cylindrical plugs are punched out of 
the plate, experiment indicates 20 that / (t/d) = (t/d) 2 . 
Although this form is compatible with the assumption 
that perforation is resisted by a constant shearing 
stress acting over the surface of the cylindrical plug 
during ejection, this picture is undoubtedly too sim¬ 
ple. A large resisting force probably acts on the pro¬ 
jectile only during the initial stages of penetration 
and then drops to a negligible value when the plug is 
formed. 

Members of the Watertown Arsenal Ballistics Labo¬ 
ratory have investigated the mechanism of plug for¬ 
mation 26,27 and suggest that the plug is not neces¬ 
sarily formed by crack propagation but may be pro¬ 
duced by plastic deformation along a surface of maxi¬ 
mum shear. The deformation is confined to a narrow 
region in the neighborhood of this surface because the 
rapid rate of increase in the stress does not allow time 
for heat conduction. As a result there is a large tem¬ 
perature rise in the region of maximum shear where 
the greatest strains occur. The temperature rise re¬ 
duces the stress required for deformation and thus fa¬ 
cilitates further deformation. Once started, the pro¬ 
cess is unstable so the plug merely slips out of the 
plate. This amounts to saying that in an adiabatic 
process the stress-strain curve in shear has a maxi¬ 
mum and that the negative slope beyond the maxi¬ 
mum corresponds to instability. 

The mechanism of plugging is different from that 
of spalling. Spalling, which consists of the ejection 
from the back face of the plate of a thin circular disk 
or irregular flakes considerably larger than the cali¬ 
ber of the projectile, usually results because of planes 
of weakness arising from excessive inclusions and in¬ 
homogeneities. Plates having such planes of weakness 
are usually eliminated during proof firing. 

Ductile Failure 

With homogeneous plate in the usual hardness 
range and projectiles having conventional nose shapes, 
the plate material is plastically deformed over a wide 
region about the point of impact; a smooth petaled 












172 


TERMINAL BALLISTICS OF ARMOR 


hole is produced and no material is thrown from the 
plate. 28 

In the case of very thin plates (less than ^-cali¬ 
ber), f(t/d) is equal to (t/d) 2 whether the plate petals 
or plugs. It has been suggested by members of the U. 
S. Naval Proving Ground 29 that in the ductile failure 
of a thin plate most of the projectile’s energy is ex¬ 
pended in bending back the petals. With the addi¬ 
tional assumption that the width of the petals is pro¬ 
portional to the thickness of the plate, the correct 
form for f(t/d) results. 

If very thick plate is used, most of the displaced 
material is pushed laterally aside rather than forward 
as in the case of thin plates. Ideally, if there were only 
lateral displacements and provided the inertial forces 
of the plate material were negligible, it would be ex¬ 
pected that f(t/d) = (t/d). This is equivalent to as¬ 
suming a constant pressure on the nose of the projec¬ 
tile. The pressure has been interpreted 31 as the hydro¬ 
static pressure necessary to expand a cylindrical hole 
in the plate by moving the material sidewise until the 
radius of the hole is equal to that of the projectile. 
Although approximately true, this ideal form of 
f(t/d) is never exactly realized in practice even for 
thick plate, one reason being that with projectiles of 
conventional nose shape some of the material is always 
pushed forward as well as sidewise. During petal for¬ 
mation at the back of the plate the forward motion 
produces cracking and bending instead of lateral plas¬ 
tic deformation. 

Present Status of Plate Penetration Theory 

At the present time there is no physical theory of 
armor penetration capable of predicting the exact 
form of f(t/d,6) for all plate thicknesses. Although 
the basic ideas and some of the details have qualitative 
explanations, 32 usable forms for f(t/d,6) must be 
obtained from firing data. 

6 53 Perforation Formulas—Normal 

Impact 

Even for the simplest type of impact (normal inci¬ 
dence, ductile failure, nondeforming projectile) no 
general analytical expression has been developed that 
systematizes the results of all recent firing tests, but 
approximate formulas can be used over restricted 
ranges in the t/d values. 29,33 ' 39,41 These approxi¬ 
mate empirical formulas are satisfactory for practical 
purposes if they are not extrapolated beyond the re¬ 
gion of experimental values used for determining the 
constants of the equations. 


One-Parameter Expressions— 
Terminal-Ballistic Coefficients 


As a method of reporting experimental data and as 
a means of removing, to a first approximation, effects 
due to changes in the weight and size of the projectile 
and to variations in the thickness of the plate, values 
are often given for ballistic coefficients. 1 The ballistic 
coefficients in common use are k, F, and C, which are 
calculated from the following equations: 


WV* 

- - = 1.932 X 

d 3 



WF ? 


d 3 


= F 2 





WVf /A 1 ' 43 

-- = 1.728 X 10 3 C - 

d 3 \dJ 


(11a) 


(lib) 


(11c) 


where multiplying factors have been used so that W 
is expressed in pounds, V t in feet per second, t in feet, 
and d in feet. Equation (11a) for k is commonly em¬ 
ployed by the L T . S. Army; equation (lib) for F, by 
the U. S. Navy; and (11c) for C, by the British Ord¬ 
nance Departments. 

All three of these expressions are special forms of 
equation (10) in which f(t/d) has been set equal to 
( t/d) n and n assigned a constant value. Since, as 
pointed out in the last section, n is equal to 2 for very 
thin plate and has a value near 1 for thick plate, any 
equation in which n is fixed requires that the ballistic 
coefficient itself depend on plate thickness. F in fact is 
often written as F(t/d). Results obtained with mild 
steel plate 37 indicate that in going from plate 0.3 to 
2.0 calibers thick, k 2 decreases by 23 percent, C by 
18 per cent, and F 2 increases by 49 per cent. Although 
ballistic coefficients are insensitive to reasonable 
changes in weight and diameter of the projectile, they 
can rarely be assigned constant values for the purpose 
of extrapolating over a wide range in plate thickness. 

Two-Parameter Formulas 

As a second approximation for f(t/d), numerous 
formulas have been proposed that permit the adjust¬ 
ment of two parameters rather than one. Among these 

are 29,34.40,41 



‘These coefficients are not to be confused with the bal¬ 
listic coefficient used in exterior ballistics. The latter was 
used in Section 6.4.2. 












STEEL AS A PROTECTIVE MATERIAL 


173 


where 


log C = C 0 — n 




WVJ ( t 

- - = Co ¬ 
rf 3 Vrf 



WV 3 



(13) 

(14) 


(15) 


For a range in t/d values from 0.5 to 2.0 there is very 
little to choose between these four equations as far as 
accuracy in representing firing data is concerned. De¬ 
spite the very different forms, the differences in pre¬ 
dicted values are of the same order of magnitude as 
the errors made in measurement. 


The region of particular interest for hyper velocity 
projectiles is for plate thicker than 2 calibers. Al¬ 
though equations of the type (12), (13), (14), and 
(15) give acceptable results for t/d between 0.5 and 
2.0 when the parameters are adjusted for this region, 
they are likely to lead to serious errors if they are ex¬ 
trapolated to large values of t/d without readjustment 
of C 0 and n. In Figure 5 are given results obtained 41 
with .244-caliber projectiles against homogeneous ar¬ 
mor (BUN 255) 1.5 to 6.2 calibers thick. Since the 
points in this logarithmic plot of WV* /d 3 against t/d 
fall on a straight line, it is apparent that the data 
in this range of plate thicknesses can be represented 
by an equation of the type of equation (13). For the 
projectile with a 1.5-caliber ogive the equation is 

WV? / t \ 126 

-^=2.73X10»(-j . (16) 



Figure 5. Logarithmic plot of specific limit energy versus plate thickness; normal impact, BHN 255 armor. 


( i U.JE.V1 JAL i 













































174 


TERMINAL BALLISTICS OF ARMOR 


A general equation of the type of equation (15), with 
C 0 and n adjusted for the range in plate thickness be¬ 
tween 0.5 and 2.0. is given in Section 6.5.6. For .244- 
caliber projectiles against homogeneous plate (BHN 
255) this equation becomes: 

WV * t 

- -- = 1.728 (694--+ 603) 2 . (17) 

d 3 d 

In the region of t/d between 1.5 and 2.0 the limit 
velocities predicted by equations (16) and (17) for 
projectiles with the same caliber density never differ 
by more than 3 per cent, which is quite acceptable 
agreement, considering that the two equations were 
established independently from entirely different sets 
of firing data 36 and with projectiles having slightly 
different nose shapes. For plate 6 calibers thick, how¬ 
ever, equation (17) leads to a limit velocity 24 per 
cent too large. On the other hand, the value of n in 
equation (16) must be decreased slightly (to approxi¬ 
mately 1.16) and the value of C 0 increased to obtain 
acceptable values for t/d between 0.5 and 1.5. In this 
regard it may be noted that for all plate thicknesses 
greater than 0.5 the value of n for plate of this hard¬ 
ness is less than that used in equations (13) and (15) 
for calculating ballistic coefficients and slightly larger 
than that used in equation (14). If n were exactly equal 
to unity, the energy required to displace a given 
volume of plate material would be constant regardless 
of the diameter of the hole ; since n is almost equal to 
unity, this is approximately true. 

In summary, there are several two-parameter for¬ 
mulas that give acceptable agreement with experiment 
for plate between 0.5 and 2.0 calibers thick, but an 
attempt to extrapolate these equations to predict 
values for thick plate without readjustment of the 
parameters may lead to serious error. For plate thicker 
than 1.5 calibers, an equation of the type of equation 
(13) with n approximately 1.25, is in agreement with 
measurements made for one hardness of plate. 

6.5.4 Perforation Formula—Oblique 

Impact 

By limiting the discussion to nondeforming pro¬ 
jectiles the case of oblique impact is almost excluded. 
For angles of attack near 40 degrees it is impossible 
with projectile materials now available to keep any 
monobloc type undeformed at velocities much above 
2,500 fps, even when the attack is against soft homo¬ 
geneous armor. Perforation limits can therefore be 
determined for a nondeforming projectile at oblique 


angles of incidence only with relatively thin plate. 

The problem of oblique attack is complicated by the 
fact that the projectile is acted on by transverse 
forces which tend to turn its axis away from the nor¬ 
mal to the plate as the nose passes through the front 
face and toward the normal as it leaves the back. This 
motion is evident from the spark shadowgraphs in 
Figure 6. As a result of this angular motion the axis 
of the hole usually makes a larger angle with the 
normal to the face of the plate than the angle of in- 



STEEL PROJECTILE PLATE IMPACT CONDITIONS 

W ■ 4.5 gm Cold rolled steel V$ - 950 f Hec 

d - .244 in. t-.19 coliber 9 •60* 

CHR • 1.5coliber? 

Figure 6. Motion of projectile during perforation of 
thin plate at oblique angle. 

cidence and the hole is elliptical in shape; the size 
of the hole and the energy absorbed by the plate is 
greater than if the projectile had not turned. At suffi¬ 
ciently large angles the projectile ricochets and in this 
case very little of the projectile’s striking energy is 
absorbed by the plate; it is merely redirected. As one 
might expect, no satisfactory general perforation for¬ 
mula exists for oblique attack by a nondeforming 
projectile, but equations have been reported 33 for one 
particular case in which the attack was against very 
thin plate. 

6 5 5 Plate Hardness 

A good index of the terminal-ballistic performance 
of armor is its hardness, which is usually specified by 
the Brinell hardness number [BIHST]. After the limit 
energy has been correlated with the average hardness 
of a plate, the chief variation in the plate’s behavior 


CONTIDEXTTAt 













STEEL AS A PROTECTIVE MATERIAL 


175 


results from inhomogeneities introduced either by 
poor heat treatment or by inclusions of foreign mate¬ 
rial. Defects resulting from inclusions are particularly 
deleterious if the plate has been extensively rolled. 
The defects are then spread out so that planes of 
weakness are produced which result in laminations. 
In the following discussion it will be supposed that 
all plates are clean and uniformly hardened. 

The resistance of a plate increases with its hardness 
up to the point where brittle failures set in. 42,43 
As the hardness is increased, the petals at the front 
and back faces are first broken off and with further 
increase plugs are ejected. Concurrently with a change 
from a ductile- to a plugging-type failure, the energy 
required for perforation by a nondeforming projectile 
decreases. Thus there is an optimum hardness for a 
given set of impact conditions, and several investiga¬ 
tions 30,44 have been carried out to determine its 
value. 

A perforation formula including the hardness of 
the plate as a parameter has been proposed 30 by mem¬ 
bers of the National Physical Laboratory (England). 
This formula is based on firings carried out with 
scale models of the 2-pounder AP shot (caliber den¬ 
sity, 0.603 lb per cu in. : nose shape, 1.4-caliber radius 
with “swell”) against plates having nominal BHN 
of 250, 300, 350, and 450, and ranging in thickness 
from 0.5 to 2.0 calibers. All shots were at normal 
incidence. 


WV> 
d 3 


_ t 


1,728 ( 43.4 V B - + 747 


54,000 
B 0 — B, 


, ( 18 ) 


where B is the Brinell hardness number, i» (1 is a con¬ 
stant for a projectile of a given size, and IE, V h cl, 
and t have the usual units of lb,fps, and ft, respectively. 

This formula agrees with the following observed 
facts: 

1. The curve of limit energy against hardness has 
a broad maximum. This means that the exact value 
of the hardness is not critical and indicates why it is 
difficult experimentally to determine an optimum 
value. 

2. The optimum hardness increases with t/d and, 
as indicated by the increase in B 0 , decreases as the 
caliber increases. The variation of B 0 with the size of 
the projectile will be considered in the next section. 
The change in optimum hardness with the projectile’s 
size, together with the fact that it is more difficult 
to make good quality hard plate in large than small 
sizes, are reasons for the common practice of making 
heavy armor softer than light armor. 


6 - 5 - 6 Scale Effect 

Nearly every terminal ballistic test involving pro¬ 
jectiles of different diameters shows that for a given 
t/d there is a slight tendency for the specific limit 
energy to decrease as the caliber of the projectile 
increases. 37,39,45 In other words, if two projectiles 
exactly the same except for size are fired against 
plates of identical armor having the same caliber 
thickness, the larger projectile has a slightly lower 
limit velocity. This scale effect contradicts equation 
(10), although not seriously since the effect is small. 

Three possibilities have been proposed as explana¬ 
tions : 

1. The simplest proposal is simply that, due to 
difficulties in heat treatment, the quality of thick 
plates is inferior to that of thin plates, so compar¬ 
isons at the same t/d result in an advantage for the 
large calibers. In certain cases this may play a part, 
but it is not the complete explanation. 

2. A second suggestion is that the effect is due 
to the decrease in the rate of strain of the target 
material with increase in caliber, smaller stresses 
being required to produce the same strain at a lower 
rate of strain. As a result of rapid rate of strain meas¬ 
urements 40 it has been shown that in armor this 
effect is too small to account for the observed differ¬ 
ences in ballistic limits. Furthermore, the scale effect 
has been produced in static punching experiments. 47 

3. The third, and most reasonable proposal, de¬ 
pends on the observation that size effects occur also 
in slow bend and impact test of notched bars. 48 " 51 
Specifically, if d is a linear dimension of the speci¬ 
men, then the work required to fracture similar speci¬ 
mens is not proportional to d 3 . It is significant that 
the size effect in static tests, just like the scale effect 
in armor, increases with brittleness: it is larger the 
greater the hardness of a given steel. Since size effects 
have been observed for fracture but not with plastic 
flow it appears likely that the region near the back 
face is the one responsible for the scale effect. Except 
for very hard or inferior plate this is the only region 
in which cracking occurs. It has been suggested that 
size and therefore the scale effect may be connected 
with the occurrence of inclusions, which are present 
to some extent even in good quality armor. 

The scale effect has been included in equation (18) 

by allowing B 0 to be a function of the diameter of the 

projectile: ( j 

B 0 = 500 — 160 log 10 —, (19) 

where d 2 = 0.1304 ft. Although a correction due to 









176 


TERMINAL BALLISTICS OF ARMOR 


a change in the caliber of the projectile is usually 
small, it may become important for hard, thin plate 
since the scale effect increases with plate hardness 
and with a decrease in the caliber thickness. As an 
indication of the magnitude of the effect, a change 
in d by a factor of 2 results in a 6 per cent change 
in the specific limit energy for 1 caliber thick plate 
with BUN 250. 


65 7 Applications of Perforation Formulas — 
The Sabot Projectile 


The perforation formulas just discussed are useful 
for predicting optimum projectile performance and 
in addition, under conditions where the projectile 
does not deform, they have the following applications: 

1. Corrections of firing trial results to a common 
hardness basis. 

2. Determination of the optimum hardness for a 


plate. 

3. Assessment of the effect of changes in the de¬ 
sign of a projectile on its perforating ability. 

With regard to the last point, it will be noted that 
all the perforation formulas indicate that with a 
given striking energy a greater thickness of plate 
can be perforated with a small than a large projectile. 
This advantage of a subcaliber projectile is partially 
offset, however, by the fact pointed out in Section 
6.4.2 that the striking energy of a subprojectile de¬ 
creases with its diameter. 

Equation (16) j will serve to estimate the relative 
importance of these two conflicting factors. If T = 
t s /t F , where t s is the limit plate thickness for the 
subcaliber projectile and t F is the limit for a similar 
full-caliber projectile, then in terms of the ratio of 
the striking energies E the perforation formula 
becomes: ///\ 1 / 1.26 

T = R (w) ■ < 20) 


As previously used, R is the ratio of the diameter of 
the sub- to that of the full-caliber projectile. Values 
of T calculated for steel projectiles fired from a 
37-mm gun are listed in Table 1 for values of R from 
1.00 to 0.54 and for ranges of 0, 1,000, and 2,000 yd. 
Corresponding values of T have also been calculated 
by assuming that the steel of the subprojectile is re¬ 
placed by tungsten carbide. The values for the tung¬ 
sten carbide cored projectiles are contained in Table 


* Plates thinner than 1.4 calibers will not be considered 
in the present application. For plate having a BHN 250 
and with no change in projectile diameter greater than 
2, the scale effect should always be small. It will be neglected 
here. 


2, where, as in Table 1, all results are given relative 
to the performance of a prototype full-caliber steel 
projectile, which is used as the standard. 

Although the figures given in Tables 1 and 2 are 
merely illustrative, they indicate the fact, borne out 
by experience, that in cases where projectile deforma¬ 
tion is not a factor a considerable increase in perforat¬ 
ing ability results from the use of subcaliber projec¬ 
tiles. They also show the effect of changing the weight 
and size of the subprojectile. 

Thus, by increasing the weight of the subprojectile, 
the replacement of steel by tungsten carbide leads to 
a real improvement; not only can a greater thickness 
of plate be perforated at the muzzle but the relative 
advantage of the tungsten carbide cored projectile 
increases with range. It will be noted that wdien de¬ 
formations are not considered the advantage of the 
tungsten carbide k is due solely to its greater density, 
which leads to a higher striking energy, and that it 
does not result because less energy is required for 
perforation. 

With regard to the size of the subprojectile, Table 
1 indicates an optimum diameter for the steel pro¬ 
jectile at each range considered. This best diameter 
increases with increase in range and at a given range 
decreases with an increase in density of the core mate¬ 
rial. Fortunately the choice of diameter is not critical; 
the “optimum” shifts slowly with range and at a 
given range the thickness of plate perforated does not 
decrease rapidly for small changes in the diameter 
near the best value. The most suitable diameter in any 
particular case depends on the approximate range 
over which the projectile is to be fired and on the 
exact type of carrier and subprojectile being con¬ 
sidered. For particulars, reference should be made to 
the original reports. 16,22 

Strictly, Tables 1 and 2 apply only to normal attack 
by monobloc projectiles, but the same trends with 
weight and size are apparent when jacketed or capped 
projectiles are used as prototypes. This results since 
the general form of the perforation equation does not 
change appreciably as protective material is added 
to the core. 

66 PERFORMANCE OF MONOBLOC 

PROJECTILES 

A general discussion of projectile deformations with 
particular reference to their dependence on striking 

k The advantage is slightly exaggerated in the present case 
because of the assumption that no heavier carrier is needed 
for a tungsten carbide than a steel core. 


COX I' 1 PE NT J 









PERFORMANCE OF MONOBLOC PROJECTILES 


177 


Table 2. Performance of subcaliber tungsten carbide projectiles as a function of core diameter. (Performance 
relative to full-caliber steel projectile of similar shape, with the same standard as used in Table 1.) 


Diameter 

ratio 

R 

Muzzle 

velocity 

Vo ' 
(fps) 

Range (yd) 

0 

1,000 

2,000 

E (0) 

T (0) 

E (1,000) 

T (1,000) 

E (2,000) 

T (2,000) 

(37 mm) 








1.00 

2,265 

1.04 

1.03 

1.16 

1.12 

1.34 

1.26 

0.90 

2,555 

0.99 

1.14 

1.10 

1.24 

1.26 

1.39 

0.80 

2,870 

0.92 

1.27 

1.01 

1.37 

1.15 

1.52 

0.70 

3,210 

0.83 

1.41 

0.90 

1.50 

1.00 

1.64 

0.60 

3,532 

0.70 

1.53 

0.74 

1.59 

o.so 

1.69 

(20 mm) 








0.54 

3,665 

0.61 

1.58 

0.62 

1.61 

0.65 

1.66 


R = 
E(x) = 
T(x) = 


subprojectile diameter 
gun diameter 

energy of tungsten carbide subprojectile at range x 
energy of similar full-caliber steel projectile at range x 
limit plate thickness of tungsten carbide subprojectile at range x 
limit plate thickness of similar full-caliber steel projectile at range x 


conditions will be given before considering effects due 
to changes in such projectile parameters as length, 
nose shape, and strength of material. Changes in these 
parameters are important mainly because they control 
deformations of the projectile; to a limited extent, 
however, changes in length and nose shape also affect 
the energy required for perforation even when the 
projectile remains intact. 

661 Projectile Deformations — Dependence 
on Impact Conditions 

On impact, the stresses in a projectile, and therefore 
its tendency to deform, increase continuously with 
increase in striking velocity. Although details of the 
resultant progressive disintegration change with varia¬ 
tions in projectile characteristics, the general pattern 
is the same for all. On striking the plate at velocities 
below a certain critical value, whose magnitude de¬ 
pends on the properties of the projectile, the type of 
armor, and the angle of attack, the projectile stays 
intact. As the velocity is increased above this value 
the projectile deforms progressively 1 * until at a suffi¬ 
ciently high velocity it completely disintegrates al¬ 
most immediately on impact. 

At a velocity (really, within a narrow range of 
velocities) somewhat above the velocity at which the 
initial failure takes place, the hole made in the plate 
changes from one of approximate projectile diameter 

1 An exception to this statement sometimes, though rarely, 

occurs when the initial failure takes place in the body of the 

projectile. Projectiles have been observed 7 to break across 

the body and fail to perforate the plate at a low velocity and 

yet perforate whole at a slightly higher velocity. 


with smooth sides to one that has a rough jagged sur¬ 
face and is greatly oversize. These two types of holes 
are shown in Figure 7. Concurrently with a change 
from a small to an oversized hole there is usuallv 

•j 

an abrupt increase in the energy required for perfora¬ 
tion. When an oversized hole is produced the nose 
of the projectile is always in several small pieces. 

The initial failure may occur either in the nose or 
in the body of the projectile. If it occurs in the body 
there is usually a considerable difference between the 
velocity at which it first takes place, the rupture 
velocity, and that at which there is a significant, 
abrupt change in the character of the hole—the shatter 
velocity. In this case there is apparently little correla¬ 
tion between the rupture and shatter velocities. If, on 
the other hand, the initial failure takes place in the 
nose, this leads directly to shatter, which occurs with 
projectiles of conventional nose shape at velocities 
only slightly higher than the rupture velocity; shat¬ 
ter as defined here m corresponds roughly to the point 

m Because of the close correlation between the rupture and 
shatter velocities in the case where initial failures take place 
in the nose, values reported for the shatter velocity sometimes 
correspond to the velocity at which the initial failure occurs 
and sometimes to the velocity at which the nose completely 
disintegrates. 5 ; 52 In fact, it has been proposed, 52 with some 
reason, that what has here been called the rupture velocity 
for nose failures be defined as the shatter velocity. The term 
shatter velocity as used in the present report has the meaning 
originally assigned to it by Milne and Hinchliffe. 3 * Shatter 
velocity defined in this way has practical importance because 
it corresponds more closely than the rupture velocity to the 
point at which there is an abrupt change in the energy ab¬ 
sorbed by the plate, but it is difficult to measure and often has 
only statistical significance. 53 


111\ i n■ i.\ I'l \i. 






































178 


TERMINAL BALLISTICS OF ARMOR 



Figure 7. Holes produced by shattered and non- 
shattered steel cores in .50-caliber arrowhead projectile. 
A. View of exit side of holes. B. Same holes after 
sectioning. Exit side of holes to the left. 



at which the whole nose of the projectile is removed. 

As the angle of attack is changed, the values for the 
two critical velocities likewise change. For a particular 
projectile and type of armor, they may be represented 
by curves 02 ' 55 such as shown in the schematic graph 
of Figure 8, where the striking velocity is given as a 
function of the angle of attack. Both curves have their 
greatest values for normal incidence and drop off with 



Figure 8. Schematic graph of critical velocities. Values 
correspond to those for tungsten carbide projectile. 58 


increase in the angle of attack; very few tests have 
been made for large angles, but at least in one case 54 
the curve for the shatter velocity flattens out for in¬ 
termediate angles and rises slightly for large angles. 

These curves are given in terms of the striking 
conditions. Their exact positions depend on nose 
shape, projectile length, and strength of projectile 
material. It seems unlikely that they depend to any 
considerable extent on the size of the projectile or its 
density, but these factors have not been thoroughly 
investigated. They are displaced to lower velocities 
when the plate hardness is increased 55 but, at least 
for plate over 1 caliber thick, are relatively insensi¬ 
tive to changes 11 in plate thickness. 5 

Examples showing the dependence of projectile 
deformation on striking conditions are given in Fig¬ 
ures 9, 10, 11, 12, and 13. It is evident from the spark 
shadowgraphs of Figures 9 and 10, showing a tung¬ 
sten carbide projectile just as it emerged from the 
back of the plate, that the projectile remained com- 

n As an exception to this, body failures in tungsten carbide 
sometimes decrease with increase in plate thickness. 56 








































PERFORMANCE OF MONOBLOC PROJECTILES 


179 



Vs=3000 FPS (SHOT NO. 29} 



V s = 1540 FPS (SHOT NO. 27) 



V s = 113 5 FPS (SHOT NO. 16) 

#=ANGLE OF ATTACK = 30° 
Vo = STRIKING VELOCITY 
(EXP. 15) 


relet; this bulge grew with increasing velocity. The 
first separation was the removal of the tip of the nose 
and at a slightly higher velocity the projectile was 
recovered in several pieces. Pictures of plate sections 
showing essentially these same stages of progressive 
disintegration are reproduced in Figure 13. 

6,6 2 Effect of Projectile Deformation on 

Perforating Ability 

Except at very large angles of impact, the increase 
in perforation energy resulting from the onset of 
shatter is considerably greater than the increase pro¬ 
duced by the body failures and the minor nose de¬ 
formations which occur in the region between the 
rupture and the shatter velocities. This effect of shat¬ 
ter is greatest at normal incidence where the increase 
in perforation energy may be as great as 100 per cent. 
Although the effect decreases as the angle of attack 



$-35° (SHOT NO. 20) 


Figure 9. Dependence of projectile breakup on striking- 
velocity. A .244-caliber tungsten carbide projectile 
(“standard”; 1-1TR) after perforating ks-in. cold- 
rolled steel (Rockwell B 94). 

pletely intact when the striking velocity and angle 
of attack were small but broke across the body when 
these quantities were increased. 58 In another series 
of shots 57 extending to higher velocities than used 
for the pictures of Figures 9 and 10, the projectile 
was fired into very thick armor; the pictures repro¬ 
duced in Figure 11 are X-ray photographs taken 
through sections cut from the armor after the impacts. 
For a particular angle of attack—note the shots at 0 
and 30 degrees—only body failures occurred at the low 
velocities, but at the highest velocity the projectile 
broke into many small pieces. The diameter of the 
holes is considerably larger than the original projec¬ 
tile diameter and the depth of penetration is much 
less than would occur with an intact projectile. At 
normal, the penetration is no greater for a striking 
velocity of 4,200 fps than for 2,600 fps. 

In contrast to the behavior of tungsten carbide, 
which suffered a body fracture, the recovered steel 
projectiles shown in Figure 12 first underwent plastic 
deformation which resulted in a bulge near the bour- 



0-- 30° (SHOT NO. 21) 



0-20° (SHOT NO. 22) 



Q--0° (SHOT NO. 23) 

Wangle of attack 
Vc = STRIKING VELOCITY = 2000 FPS 
(EXP. 15) 

Figure 10. Dependence of projectile breakup on angle 
of attack. A .244-caliber tungsten carbide projectile 
(“standard”; 1-1TR) after perforating ks-in. cold- 
rolled steel (Rockwell B 94). 


ni.VI'l 







STRIKING VELOCITY IN FPS 


180 


TERMINAL BALLISTICS OF ARMOR 


4200 



2600 









Figure 11. X-ray photographs of penetrations by .244-caliber tungsten carbide projectile into homogenous 
(BHN 266). 


LCS 


projectile 




Composition: 75 per cent tungsten carbide 
25 per cent cobalt 
Hardness: Rockwell A 85 
Transverse rupture strength: 375,000 psi 
Density: 13.0 g per cu cm 
Mass: 6.9 g 


armor 















































































PERFORMANCE OF MONOBLOC PROJECTILES 


181 


0.260 


0.250 

w 

Ui 

X 0.256 

z 
u. — 

O 2 

tr- 0-254 

UJ UJ 
H _l 

|S 0.2S2 
° o 

2 a: 

rjQ- 0.250 

< to 

5 5 0.248 
> 
o 
o 

UJ 

«t 0.246 


0.244 

2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700 3200 

STRIKING VELOCITY IN FPS. 



STEEL PROJECTILE HOMOGENEOUS PLATE 










o 


ce 

UJ 

•- 












< 

X 

W 



















u 





















( 

3 





















o 













ORIGINAL DIAM - 0.244 IN 
WEIGHT - 5.00 G 


CRH - 1.5 

HARDNESS - RC 60-63 


THICKNESS - 1.99 CALIBERS 
HARDNESS - BHN 265 


Figure 12. Deformation of steel projectiles as function of striking velocity (0° obliquity). 


increases until at very large angles (greater than 50 
degrees for 1-caliber plate) the energy required for 
perforation by a shattered projectile may actually be 
less than for a projectile that remains undeformed, 0 
it is still significant for angles of attack at least as 
great as 45 degrees. 

When a projectile is fired at a velocity above its 
shatter velocity its performance as a function of 
range (or striking velocity) may conveniently be de¬ 
scribed by means of graphs such as shown in Figure 
14. In this graph 5 the performance is given for a par¬ 
ticular angle of attack in terms of the striking veloc¬ 
ity and thickness of plate; by means of three curves, 
the shatter-velocity curve, the curve representing the 
limit velocity with shatter, and the curve for the limit 
velocity without shatter, the graph is divided into four 
regions. These regions are designated by Roman nu¬ 
merals and indicate the following results: 

I No perforation, no shatter. 

II Perforation, no shatter. 

III No perforation, shatter. 

IV Perforation, shatter. 


All four of these results do not occur for all thick¬ 
nesses of plate. Thus if the plate is thin, result III 
cannot be obtained regardless of the striking velocity; 
even though shatter occurs it does not prevent per¬ 
foration and the projectile will defeat thin plate at all 
velocities above its limit as an unshattered projectile. 
For thick plate, result II is missing; it is impossible 
in this case to perforate the plate without shatter and 
with shatter only at very high striking velocities. 
With plates of intermediate thickness, between 0.8 
and 1.35 in. in the present example, all results are 
possible; the projectile can perforate plates of these 
thicknesses at relatively low velocities (at long range) 
but will fail at higher velocities (at short range) 
because of shatter. At still higher velocities perfora¬ 
tion can again be achieved in spite of shatter, al¬ 
though, as in the case illustrated, these velocities are 
often above the muzzle velocity of the gun. When per¬ 
foration can be obtained at velocities above and below 
but not within a certain interval, the interval is called 
a shatter gap . 

The shatter velocity in the above example is much 


























182 


TERMINAL BALLISTICS OF ARMOR 


higher than usually encountered because the graph is 
based on data obtained at normal incidence with a 
sharp-nosed projectile. With projectiles having more 
conventional nose shapes, or in oblique attack, shatter 
may occur at velocities even below the muzzle veloc¬ 
ities of full-caliber projectiles fired from standard 
guns. It was mentioned in the introduction that the 
2 -pounder projectile used by the British in the Liby¬ 
an campaign failed to perforate German tanks when 
fired at point-blank range but was successful at long 



A. Striking velocity: 2,795 fps, core rebounded badly 
bent but intact, section at 55° to normal. B. Striking 
velocity: 3,190 fps, section at 40° to normal. A and B. 
No perforation, no shatter. C. Striking velocity: 3,385 
fps, section at 35° to normal, tip of nose embedded in 
plate. Perforation, no shatter. D. Striking velocity: 
4,140 fps, section at 10° to normal, rear portion of 
core remained in plate but was removed when photo¬ 
graphed. No perforation, shatter. E. Striking velocity: 
4,355 fps, section at normal. Perforation, shatter. 


ranges. This resulted from the occurrence of a shatter 
gap which extended well below 3,000 fps. 

Graphs similar to that of Figure 14 may be drawn 
for oblique angles of incidence as well as for normal. 
As the angle of attack is increased, more energy is re- 



Figure 13. Transition from unshattered to shattered projectile with increasing velocity (0° obliquity). 

























PERFORMANCE OF MONOBLOC PROJECTILES 


183 


quirecl for perforation, so the two curves representing 
the limit velocities are displaced upward; on the other 
hand, the shatter velocity decreases with increase in 
the angle of incidence so this curve is displaced down¬ 
ward. The result of these displacements is illustrated 
by the curves for 0, 20 and 30 degrees, reproduced 5 
in Figure 15. The results of shots at 20 degrees for 
a thickness of plate including a shatter gap are shown 
in Figure 13. At the larger angles the shatter gap 
occurs at lower velocities and with thinner plate, but 
its extent is less because the difference between the 



O 0.5 1 1.5 


ARMOR THICKNESS IN INCHES 

Figure 14. Perforation limits and shatter velocities at 
0° obliquity. Steel cores of .244 caliber against homo¬ 
geneous armor, BHN 255-295. 52 

Region I: No perforation, no shatter. 

Region II: Perforation, no shatter. 

Region III: No perforation, shatter. 

Region IV: Perforation, shatter. 

energy required for perforation with and without 
shatter has decreased. Thus with increase in the angle 
of attack it becomes more difficult to prevent shatter 
since it occurs at lower velocities (at least for 0 < 40 
degrees) but its effect in limiting perforation becomes 
less. 

The effect of firing a projectile at a velocity above 
its shatter velocity is only to increase its effectiveness 
at long range at the sacrifice of good performance near 
the muzzle; there is no overall gain. Particularly at 
hypervelocities, prevention of shatter for angles at 
least up to 45 degrees is the principal problem in the 
design of armor-piercing projectiles. Avoidance of less 
extensive deformation, such as a simple body failure, 
is of secondary, although sometimes not negligible, 
importance. 


6,63 Projectile Parameters 

As mentioned in the introduction of this chapter 
the parameters of a monobloc projectile may be con¬ 
sidered as its size (diameter d ), its length (either 
total length or length of cylindrical section l 0 ), its 
nose shape (specified for tangent ogive by the caliber 
radius r 0 ), its density and strength of material (usu¬ 
ally measured in terms of hardness and bend or trans¬ 
verse rupture strength). The shape parameters are 
shown in Figure 1. 

To be able to specify a completely rational projec¬ 
tile design the effect of changes in each of these quan¬ 
tities on perforation limits should be quantitatively 
known; at present it is usually possible to indicate 
only the trends to be expected. 

Strength of Material 

Projectile failures obviously result from a lack of 
mechanical strength. The causes of failure are re¬ 
viewed in a series of reports from the Watertown 
Arsenal. 26,52,64 It is pointed out that a failure usu¬ 
ally occurs as a result of (1) shearing stresses in the 
nose, (2) lateral expansion near the bourrelet pro¬ 
duced by axial compressive stresses, or (3) tension in 
the outer layers of the body resulting from bending. 
To resist the shearing and compressive stresses and 
thus prevent nose failures the material should have a. 
high hardness; to prevent body failures it should have 
a high-bend (or transverse-rupture) strength. Un- 



O 0.5 1 1.5 


ARMOR THICKNESS IN INCHES 

Figure 15. Perforation limits and shatter velocities at 
0°, 20°, and 30° obliquity. Steel cores of .244 caliber 
against homogeneous armor, BHN 255-295. 52 


£0X1: I (il'.XlM Ug 






























































































184 


TERMINAL BALLISTICS OF ARMOR 


fortunately maximum bend strength usually cannot 
be obtained simultaneously with maximum hardness. 

J 

To alleviate this difficulty steel projectiles are given 
a differential heat treatment. The nose is kept hard 
but the body softened to allow plastic deformation, 
which relieves the tensile stresses in the outer fibers. 
By this means it is often possible to prevent body fail¬ 
ures in steel projectiles without increasing the likeli¬ 
hood of nose failures. This is essential because a nose 
failure leads immediately to shatter, which is much 
more disastrous than a body failure. 

In the case of cemented tungsten carbide projectiles, 
the highest transverse-rupture strength that can be 
obtained, even by sacrificing hardness, 0 is so low that 
body failures occur at extremely low velocities. Thus 
the initial failure taking place at the rupture velocity 
is invariably a fracture across the body. The nose 
remains intact, however, until the shatter velocity is 
reached, whereupon the whole projectile disintegrates. 
A series of tests 57,58 carried out with cemented tung¬ 
sten carbide projectiles of different compositions has 
shown that, as one would expect, the shatter velocity 
increases with increasing hardness, while the rupture 
velocity is increased by an increase in transverse- 
rupture strength. Since by changing the composition 
a decrease in transverse-rupture strength always ac¬ 
companies an increase in hardness, the shatter veloc¬ 
ity can be raised by this means only at the expense 
of lowering the rupture velocity. This decrease in the 
rupture velocity is usually of no practical importance, 
however, since it is so low in any case that body fail¬ 
ures cannot be prevented with projectiles of conven¬ 
tional length under conditions of impact likely to be 
encountered in combat. 

For perforation of single thicknesses of homogene¬ 
ous armor the best composition of tungsten carbide is 
the one giving the highest hardness. High hardness 
is obtained by cementing the tungsten carbide par¬ 
ticles together with a small amount of binder and 
this, fortunately, leads to a high density, which is an 
added advantage. If the target consists of spaced 
plates, other considerations indicate that a different 
choice mav be advisable. 57 

Nose Shape 

Although the ultimate reason for projectile failure 
is low mechanical strength, the shatter and rupture 
velocities may also be varied by changes in other para- 

0 .Although attempts have been made at adjusting the 
hardness and transverse-rupture strength along the length 
of a tungsten carbide projectile, these trials have not proved 
successful. 64 


meters. While mechanical strength is important only 
with respect to deformations, changes in the other 
variables may also affect the energy required for per¬ 
foration when the projectile stays intact, or the energy 
and velocity with which the projectile strikes the 
plate. 

Changes in nose shape will not affect the striking 
energy, provided the total projectile weight is kept 
constant and a windshield is used to keep the external 
contour the same. Thus the two most important cri¬ 
teria of goodness are: (1) high shatter velocity and 
(2) low perforation energy for the intact pro¬ 
jectile. 41,52,00 ' 62 

In Table 3 are given the shatter velocities against 
homogeneous armor at 0, 15, 22.5, and 30 degrees for 
steel projectiles having tangent ogives with caliber 

Table 3. Dependence of shatter velocities (fps) on 
nose shape and angle of attack. Steel projectiles, ho¬ 
mogeneous plate (BHX 341).* 


Caliber ogive 


Angle 
of attack 
(degrees) 

3.0 

1.5 

1.27 

1.0 

1.27 

and 

0.2f 

0 

4,000+ 

3,400+ 




15 

.... 

3,200 

3,050 

2,600 

2,350 

22.5 

.... 

2,750 

2,600 

2,500 

2,200 

30 

2,000 : 

2,400 

2,350 

2,450 

2,200 


*Values taken from Watertown Arsenal results given in reference 53. 

These are actually rupture velocities. 
fDouble radius ogive with spherical tip. 
lEstimated from results in reference 62. 

radii of 3.0, 1.5, 1.27, and 1.0, and also for a projec¬ 
tile with a 0.2-caliber spherical tip used in conjunction 
with 1.27-caliber tangent ogive. 52,62 At normal, the 
projectile with the largest caliber radius, that is, the 
one with the most pointed nose, has the highest shat¬ 
ter velocity. At 30 degrees the situation is reversed; 
of the projectiles with a simple tangent ogive, the one 
with the smallest caliber radius now has the highest 
shatter velocity. Thus, as far as avoidance of shatter 
is concerned, it is an advantage to make the projectile 
quite pointed for normal attack but blunt for a 30- 
degree angle of incidence. For larger angles of attack 
the order may again reverse. 52 

If the shapes are rated on a basis of the energy re¬ 
quired for perforation when the projectile stays in¬ 
tact. the large-radius ogive is again best at normal. 
Thus in normal attack of homogeneous armor 4 cal¬ 
ibers thick the limit energy of a projectile with a 1.5- 
caliber radius is 15 per cent greater than for one with 
a 5.0-caliber radius : 41 this advantage decreases with 


eOXFIPEXTIAL 


























PERFORMANCE OF MONOBLOC PROJECTILES 


185 


plate thickness, but the difference is still 4 per cent 
for 1-caliber plate. At high obliquities, projectiles 
with a large radius ogive have a greater tendency to 
scoop ; since this leads to a higher limit energy, a 
blunt-nosed projectile becomes best under these con¬ 
ditions. 

On a basis of both ratings, high shatter velocity or 
low limit energy, a large radius has an advantage for 
near-normal attack but not for oblique attack. Obvi¬ 
ously a choice of the best shape cannot be made unless 
the conditions of impact are exactly specified. A rela¬ 
tively blunt nose, 1.25- to 1.5-caliber radius, is usually 
chosen because of the difficulty of avoiding shatter 
at obliquities between 30 and 45 degrees. Even with a 
blunt nose, however, shatter cannot be prevented at 
high striking velocities without the use of a cap. 

The above discussion was concerned with a single 
radius ogive. It will be seen from Table 3 that a 
rounded tip leads to lower shatter velocities at all 
angles of obliquity; since this shape in no case results 
in an appreciably lower limit energy, a rounded tip 
should be avoided. Flat-ended projectiles are even 
more likely to shatter so that they can only be used 
at very low velocities and therefore against very thin 
plate; under these conditions, however, they require 
considerably less energy for perforation than projec¬ 
tiles with ogival heads. 30 

Length 

Because of a decrease in the weight of the projectile, 
a decrease in length leads to a lower striking energy and 
a higher striking velocity. The writer knows of no tests 
which show the exact dependence of the shatter veloc¬ 
ity on length, but it seems unlikely that it is appreci¬ 
ably affected. Certainly if the projectile is too short 
it will fail by shatter because of the high striking 
velocity. This furnishes a basis for an absolute lower 
limit for the length; an upper limit is set by stability 
considerations. 

If body failures occur for lengths intermediate be¬ 
tween these two extremes, a choice must be made be¬ 
tween the greater striking energy obtained with a long 
projectile and the smaller tendency toward body fail¬ 
ures resulting from a short projectile. As an example 
of the effect of length on the occurrence of body fail¬ 
ures, 58 a decrease in the body length of a tungsten 
carbide projectile from 2.75 to 1.25 calibers increased 
by over 300 per cent the energy at which it could be 
fired through homogeneous plate at 30 degrees with¬ 
out breaking. Since a body failure usually does not 
greatly increase the energy required for perforation, 


it is often difficult to decide on the best length 59 
unless the projectile can and must be kept completely 
intact. 

Conventional lengths for monobloc steel projectiles 
and tungsten carbide cores are about 3.5 calibers over¬ 
all, with body lengths a little over 1 caliber shorter. 
The cores for capped steel projectiles are usually 
shorter than 3.5 by V 2 to 1 caliber. 

Density 

As with an increase in length, an increase in density 
of the projectile results in a higher striking energy 
but a lower striking velocity; the lower striking ve¬ 
locity reduces the likelihood of shatter. 

The most important change in density encountered 
in projectile design occurs when tungsten carbide is 
substituted for steel. It is interesting that it is the 
high density of tungsten carbide, rather than its bet¬ 
ter mechanical properties, that is responsible for its 
superior perforating ability. Although the shatter ve¬ 
locity of a tungsten carbide projectile is not much 
greater than that of a good steel, it can have almost 
twice the striking energy without shattering because 
of its greater weight. Thus the high density of tung¬ 
sten carbide leads to two distinct advantages: (1) a 
greater striking energy and (2) a higher shatter en¬ 
ergy. It is essential, of course, that an increase in den¬ 
sity not be accompanied by a decrease in strength; 
lead, for example, is a poor projectile material in spite 
of its high density. 

Another effect of a change in density, or more pre¬ 
cisely of a change in weight, is of secondary impor¬ 
tance, but will be mentioned for the sake of complete¬ 
ness. This effect is concerned with the energy required 
for perforation when the projectile does not shatter. 
Equation (10) should apply in this case and this equa¬ 
tion assumes that the limit energy is independent of 
the weight of the projectile. This has been shown to 
be true 41 for normal attack of plate thicker than 1.5 
calibers but for thinner plate the limit energy in¬ 
creases slightly with increase in projectile weight. 37,41 
For 1-caliber plate an increase in weight by 50 per 
cent increased the limit energy of a projectile with a 
1.5-caliber radius by slightly more than 8 per cent. 

Size 

A change of size is obviously of importance in de¬ 
sign only in the case of subcaliber projectiles. As a 
result of the increase in striking velocity with a de¬ 
crease in size, shatter often occurs before the optimum 
diameter calculated by the method of Section 6.5 is 


1 <J>.i !:>KXTIAiJ 









186 


TERMINAL BALLISTICS OF ARMOR 


reached. A case in which the occurrence of shatter de¬ 
termines the most suitable size for a subcaliber capped 
steel projectile is considered m Section 6.8. The 
shatter velocity of a monobloc steel projectile is so low 
at obliquities that even a full-caliber projectile of this 
type is ineffective if fired from a present day standard 
gun in the important range between 20 and 45 de¬ 
grees. Monobloc tungsten carbide projectiles might 
conceivably be used in subcaliber sizes if the striking 
velocity was limited to values below about 3,000 fps 
and the attack restricted to homogeneous plate. If the 
projectile and gun were the types considered in cal¬ 
culating Table 2, a muzzle velocity of 3,000 fps would 
correspond to a subprojectile to gun diameter ratio 
of 0.75. 


67 COMPARATIVE PERFORMANCE OF 
CAPPED AND MONOBLOC PROJECTILES 

The purpose of the cap is to prevent shatter. In 
cases where the monobloc does not deform badly or 
where shatter aids perforation, the use of a cap is a 
detriment. On the other hand, if deformation greatly 
reduces the perforating ability of the monobloc, then 
the cap, by keeping the main body of the projectile 
intact, may decrease the limit energy for the projec¬ 
tile as a whole despite some loss in penetrating ability 
due to its own disintegration. Thus the limit energy 
may be either increased or decreased by the attach¬ 
ment of a cap and unless the conditions of impact are 
exactly specified, no answer can be given to the ques¬ 
tion of whether a capped or a monobloc projectile per¬ 
forates a greater thickness of armor. 

For attack of face-hardened plate the cap is useful 
at all striking velocities. Against soft homogeneous 
plate (BHN 250) the monobloc has the advantage at 
low velocities (less than approximately 2,500 fps for 
steel projectiles), but the capped projectile can per¬ 
forate thicker plate at velocities above the shatter ve¬ 
locity of the monobloc at normal incidence (for steel 
projectiles usually above 3,500 to 4,500 fps, depending 
on nose shape). Whether or not the cap is of benefit 
at velocities intermediate between these two extremes 
depends on the angle of attack. 

A comparison of the performance of a capped and a 
monobloc steel projectile of equal total weights is 
given in Figure 16 for a particular striking velocity 
in the intermediate range. 6,66 The graph indicates 
the thickness of plate perforated by each projectile as 



O 10 20 30 40 50 60 70 


ANGLE OF ATTACK IN DEGREES 

Figure 16. Comparative performance of capped and 

monobloc projectiles against homogeneous armor. 

a function of the angle of attack. For small angles the 
monobloc perforates thicker plate. The advantage of 
the capped type, whose piercing element remains in¬ 
tact at all obliquities, begins at and is greatest for an 
angle just larger than that at which the monobloc shat¬ 
ters. As the angle is increased beyond the critical angle 
for shatter the difference between the thickness of ar¬ 
mor perforated by the two types gradually decreases 
until it becomes zero. At still greater angles (greater 
than 55 degrees in the present case) the shattered 
monobloc perforates the most armor. Thus in the in¬ 
termediate velocity range the monobloc is superior at 
large and small but not at intermediate angles; the 
capped projectile becomes superior at smaller angles 
as the velocity is increased. 

Although the exact amount by which the shatter 
velocity is raised by means of a cap depends on many 
factors, particularly cap weight, there is no doubt as 
to the general effectiveness of the method for reducing 
deformations. To cite one case, 67 a particular cap (27 
per cent of core weight) increased the shatter velocity 
of an uncapped projectile fired against homogeneous 
armor from less than 2,400 fps to approximately 4,100 
fps; the cap was equally effective in increasing the 
shatter velocity at all angles of attack from 0 to 60 
degrees. The addition of the cap in this case reduced 
the perforating ability of the projectile only for plate 
less than 2 calibers thick because even at normal in¬ 
cidence the uncapped projectile could perforate plate 
no thicker than this without shatter. For 1-caliber 
plate at normal incidence the cap increased the limit 


I U.\ l ii'I.N i'l \l* 
























HYPERVELOCITY PROJECTILES 


187 


velocity by 10 per cent and the limit energy by 54 per 
cent. This effect of the cap in increasing the limit ve¬ 
locity becomes less for thicker plate. 65 

The relative performance of a number of full-cali¬ 
ber monobloc and capped steel projectiles is shown in 
the graphs of the Division 2, NDRC, Data Sheets 
2C3a (Chapter 19). These are standard projectiles 
fired from standard guns at velocities below 3,000 fps. 
The curves, which give the thickness of homogeneous 
armor that can be perforated at various ranges, were 
purposely not begun at zero range because the projec¬ 
tiles had not been tested at velocities as high as the 
muzzle velocities. Extrapolations would probably be 
justified for both the capped and monobloc projectiles 
at 0 degree obliquity and for the capped but not the 
monobloc at 30 degrees. For example a test 6 of the 
monobloc 37-mm M74 showed that at point-blank 
range it would shatter and perforate only 2.2 in. at 
30 degrees while extrapolation of the 2C3a graph in¬ 
dicates that it should defeat 3-in. plate. Another point 
is that the performance of the monobloc projectiles is 
worse at long ranges than that of the capped projec¬ 
tiles. This might appear to contradict earlier state¬ 
ments that a monobloc is better at low velocities. The 
cause for the poor performance of the monobloc in 
this case, however, is not its poor terminal-ballistic 
behavior but the fact that only the capped projectiles 
have windshields. 

The above examples are for steel projectiles. That 
the addition of protective material is also effective in 
the case of tungsten carbide cores was well demon¬ 
strated during the development of a hypervelocity 
projectile for the 6-pounder, 7-cwt, 57-mm gun. 68 
During this development, a comparative terminal-bal¬ 
listic test was carried out with projectiles of two types. 
One had a comparatively heavy steel windshield and 
Duralumin pad covering the nose of the tungsten 
carbide core while the other had only a light Dura¬ 
lumin windshield. At 4,150 fps, which was the muzzle 
velocity of the gun, the projectile with the heavy steel 
windshield was able to perforate approximately 25 per 
cent more armor at all but near-normal obliquities. 

Actually the tungsten carbide cored projectiles used 
in the 57-mm gun were jacketed rather than capped. 
In either case, however, the essential feature necessary 
for good performance is sufficient protective material 
surrounding the nose of the core. The portion of the 
jacket surrounding the sides of the core apparently 
has little effect in controlling breakup, 69 and presum¬ 
ably this is also true for the material behind the core. 


/ 

In cases where the core does not shatter, however, 
material behind the core often contributes to the pene¬ 
tration by giving the core a boost from behind when 
it strikes the plate. 5 Thus the results given for per¬ 
foration limits of tungsten carbide cored projectiles 
in the Division 2, NDRC, Data Sheet 2C6 of Chap¬ 
ter 19 are sometimes less than would be computed 
from equation (16), not only because of a slight scale 
effect but also because of contributions from the 
jackets It should be pointed out that the band in this 
graph marked “capped” should apply to any projectile 
which has sufficient material to protect the nose 
whether it has a cap in the conventional sense or not. 

68 HYPERVELOCITY PROJECTILES 

As previously indicated, armor-piercing projectiles 
are conventionally classified as monobloc, capped, or 
jacketed, and either steel or tungsten carbide is cus¬ 
tomarily used for the piercing element (core). Con¬ 
ceivably any of these six possible types might be em¬ 
ployed as a full-caliber or as a subcaliber projectile,* 1 
but, with the exception of small arms ammunition, the 
only types used in combat during World War II were 
full-caliber capped and monobloc projectiles made en¬ 
tirely of steel and jacketed tungsten carbide projectiles 
in both full and subcaliber sizes. Except for experi¬ 
mental purposes and in the case of one gun, the Ger¬ 
man 88-mm, steel projectiles were not used at hyper¬ 
velocities. The possibility of a hypervelocity, subcali¬ 
ber steel projectile will be discussed, however, in order 
to compare results with those obtained with tungsten 
carbide cored projectiles which were used exclusively 
at hypervelocities. 

6 81 Steel Projectiles 

Normally the full-caliber steel projectiles have 
muzzle velocities below 3,000 fps. The monobloc is 
ruled out for use at higher velocities because of the 
likelihood of shatter. The capped projectile is less 
likely to shatter than the monobloc and can be suc¬ 
cessfully used as a full-caliber projectile in somewhat 
more powerful guns, but only a small advantage is 
gained by using it as a subcaliber projectile. 

The graph in Figure 17 shows the thickness of ar¬ 
mor that can be perforated at the muzzle of a 37-mm 

p Following customary practice, the specific limit energies 
and caliber plate thicknesses in this graph are based on core 
weight and diameters. 

Q As used here, subcaliber means that the diameter of the 
projectile in flight is less than the diameter of the gun. 


CONFIDEXTIAT# 









188 


TERMINAL BALLISTICS OF ARMOR 


a: 

Ui 

m 

< 

o 

i 

a> 

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a: 

UI 

m 

_i 

< 

o 

i. 


CO 

CO 

LjJ 


2 * 

of 

o W 

h- < 
< _J 
cc a 



5.0 

4.5 


■ 4.0 


■ 3.5 


3.0 


co 

a. 


ro 

O 


O 

o 

_J 

LU 

> 

Ui 

_J 

N 

N 

O 


DIAMETER RATIO 


SUB-CALIBER 

FULL-CALIBER 


Figure 17. Perforation limits as function of diameter of subcaliber projectiles. Homogeneous armor attacked at 
point-blank range. 


gun by subcaliber capped steel projectiles of the same 
shape but different sizes. 6 This curve was calculated 
by the method outlined in Section 6.5 but is based on 
a perforation formula obtained from firing trials with 
a projectile of the particular type and shape consid¬ 
ered in this example; the curve should hold at obli¬ 
quities as well as at normal. It will be noted that even 
though the cap in this case is very heavy (27 per cent 
of core weight), shatter sets in before the optimum 
diameter is reached. In order to avoid shatter at the 
muzzle the subprojectile to gun diameter ratio should 
not be greater than about 0.7; furthermore, at 2,000 
yd a core of this size would give better performance 
than smaller cores even though deformation is not a 
factor at this range. If a subprojectile with a diameter 
ratio of 0.7 were a scale model of the full-caliber pro¬ 
jectile, it should perforate approximately 30 per cent 
more armor at the muzzle and 20 per cent more at 
2,000 yd. Actually, however, it is not necessary to use 
a cap as heavy as this for the full-caliber projectile; 
the cap of the 37-mm M51 is only 14 instead of 27 
per cent of the core weight. Consequently the advan¬ 
tage at the muzzle of the subcaliber projectile over the 
M51 is only 18 rather than 30 per cent, and this ad¬ 
vantage decreases with increase in range. In this ex¬ 


ample the muzzle velocity for the full-caliber projec¬ 
tile is 2,900 fps; in the case of a more powerful gun, 
the subprojectile would be limited to even larger di¬ 
ameters and its advantage would be still less. In fact, 
if the power of guns is increased any considerable 
amount above the present level even the full-caliber 
projectile will be unsatisfactory unless means of in¬ 
creasing the strength of steel are found. 

6.8.2 Tungsten Carbide Cored Projectiles 

There are three conventional types of jacketed tung¬ 
sten carbide projectiles: (1) the folding skirt pro¬ 
jectile, (2) the composite rigid or arrowhead, and (3) 
the sabot. Due to their very small total weight all have 
muzzle velocities in the hypervelocity range even when 
fired from standard guns. Likewise all have about the 
same terminal-ballistic performance which is deter¬ 
mined to a first approximation by the size and weight 
of the core. In other respects each has its own advan¬ 
tages and disadvantages. 

Folding Shirt. This projectile is fired through a 
tapered bore which may either be built into the gun or 
added to a standard gun by means of a special muzzle 
attachment. The taper serves to swedge down flanged 


( OXFIDENTIAI! 






































HYPERVELOCITY PROJECTILES 


189 


skirts, which extend from the main body of the pro¬ 
jectile so that the emergent caliber is much less than 
the original diameter. In this way the accelerating 
pressure of the powder gases is allowed to act on a 
large area while a small area is presented to the re¬ 
sisting pressure due to air resistance. The principal 
disadvantages of this means of obtaining hypervelo¬ 
cities is that the taper prohibits the use of standard 
ammunition. 

Composite Rigid. This is merely a light-weight full- 
caliber projectile with a tungsten carbide core having 
a diameter approximately half that of the gun. Due 
to a very low ballistic coefficient it rapidly loses ve¬ 
locity in flight so that it is effective only over a very 
short range. 

Sabot. The principal disadvantage of the sabot is the 
danger that the discarding pieces will strike friendly 
troops. Although the high ballistic coefficient of the 
subprojectile makes it effective over a much longer 
range than the composite rigid, it is not so accurate 
at the present stage of development. 

That practical projectiles of these designs are sig¬ 
nificantly superior in perforating ability to conven¬ 
tional full-caliber types has been demonstrated both 
in combat and by plating trials. The most recent esti¬ 
mates for the performance of various armor-piercing 
projectiles against German tanks 72 indicate that for 
every gun considered (76-mm, 7.7-mm, 90-mm, 17- 
pounder, 3.3-in.) the composite rigid and sabot pro¬ 
jectiles are more effective than the corresponding full- 
caliber steel projectiles. Contrary to the opinion that 
tungsten carbide projectiles are inferior at oblique 
angles of incidence, their superiority exists at 55 de¬ 
grees obliquity as well as at normal, although not to 
the same extent. 

A second example showing the increase in perforat- 



O 10 20 30 40 50 60 70 


ANGLE OF ATTACK IN DEGREES 

Figure 18. Comparative performance of sub- and full- 
caliber projectiles. A 37-mm M3 gun, point-blank range, 
homogeneous armor BHN 260 ± 20. See Table 4 for 
complete projectile descriptions. 


ing ability to be expected from the use of tungsten 
carbide cored projectiles is given in the graph of Fig¬ 
ure 18, which is based on firing trials carried out by 
Division 2, NDKC. This graph indicates the thick¬ 
ness of homogeneous armor that can be defeated at 
the muzzle of a 37-mm gun as a function of the angle 
of attack. Limit thicknesses are given for three pro¬ 
jectiles: (1) full-caliber capped steel 37-mm M51, 
(2) subcaliber capped steel, and (3) subcaliber 
jacketed tungsten carbide, model of 6-pounder dis¬ 
carding sabot [DS] Mark I. A description of these 
projectiles is given in Table 4. The full-caliber type 
is the standard service projectile for this gun; the sub- 


Table 4. Description of projectiles whose perforating ability is given in Figure 18. 


Projectile 

type 

Full-caliber capped-steel 

37-mm M51 APC 

Discarding sabot, 
capped-steel subprojectile 

Discarding sabot, 
jacketed tungsten carbide 
subprojectile 

(Model of 6-lb DS, Mark I) 

Components 

Complete 

Windshield 

Cap 

Core 

Complete 

Subprojectile 

Complete 

Subprojectile 


Windshield 

Cap 

Core 

Jacket 

Core 

Weight (lb) 

1.87 

0.03 

0.23 

1.61 

0.85 

0.01 

0.14 


0.53 

0.88 

0.23 

0.43 

Diameter 

(in.) 

1.46 

.... 

.... 

1.46 

1.46 

.... 

• • • • 


1.02 

1.46 

0.95 

0.72 

Muzzle 

velocity 

(fps) 

2,920 

4,110 

4,050 


I OXFIlJKNTIAi.; 















































































190 


TERMINAL BALLISTICS OF ARMOR 


caliber steel projectile is the one whose performance 
was discussed in the preceeding section; the tungsten 
carbide cored projectile is representative of good de¬ 
sign for this type, although the writer has seen no re¬ 
port indicating that the diameter of the core has been 
adjusted for optimum size. At normal the tungsten 
carbide cored projectile is able to perforate 60 per cent 
more armor than the full-caliber projectile; while the 
advantage drops with obliquity, it is still 22 per cent 
at 55 degrees. 

69 FUTURE STUDIES 

A person thoroughly familiar with the results of the 
many plating trials carried out during the past few 
years should be able to suggest a good basic design and 
reasonable values for the parameters of either a full or 
•a subcaliber projectile to be fired against simple tar¬ 
gets from a present-day gun. Adjustment of the para¬ 
meters on a basis of firing trials may well be necessary, 
however, before acceptable performance is obtained. 
The designer will find his task difficult (1) if the 
power of the gun is much above the present level, (2) 


if the main armor of the target is protected by a thin 
skirting plate, or (3) if the armor plate is set so that 
it can be struck only at a large angle of incidence. 

If higher striking velocities are to be employed, 
better means must be found for keeping the projectile 
intact. Every effort should be made to increase the 
strength of projectile materials and more satisfactory 
methods should be devised for preventing the decap¬ 
ping 55 and breaking of projectiles 71 by skirting plates. 

Special attention should be given to high-angle at¬ 
tack. At the end of World War II it was impossible 
with the best antitank guns and projectiles available 
to defeat the sloping plates on the front of German 
tanks except at short range. 

At the present time projectile design must be car¬ 
ried out almost entirely on a basis of empirical results. 
Particularly for oblique attack, the fundamental prob¬ 
lem of finding the forces involved in the plate-projec¬ 
tile interactions has hardlv been touched. Once these 

•j 

forces are known it should be possible to deduce the 
dynamic stresses produced in the projectile during 
impact and to design rationally against the resulting 
deformations. 


I 







Chapter 7 


TERMINAL BALLISTICS OF CONCRETE 


71 INTRODUCTION 

711 The Work of CPPAB and CFD 

esearch on the terminal ballistics of concrete^ 
was begun at Princeton late in 1940 under the 
auspices of the Committee on Passive Protection 
against Bombing [CPPAB]. 1 This Committee was 
appointed by Frank B. Jewett, President of the 
National Academy of Sciences, on June 24, 1940, to 
supervise the execution of a one-year contract entered 
into July 1, 1940, by the United States of America 
and the National Academy of Sciences. This contract 
called for the National Academy of Sciences to make 
reports to the Chief of Engineers, U. S. Army, cover¬ 
ing “the basis of design of structures to provide pro¬ 
tection to personnel and installations, both military 
and civil, against bombing by aircraft.” The contract 
was subsequently renewed by the Corps of Engineers 
in July 1941, July 1942, and July 1943. In the latter 
contract, terminating October 31, 1944, the name was 
changed to Committee on Fortification Design [CFD] 
to correspond more closely to the then-current objec¬ 
tives of the committee’s work. 

Almost from the beginning this work was closely 
integrated in many of its phases with the research 
programs of Sections B and S of Division A of NDRC 
and later of Division 2 after the reorganization of 
NDRC in January 1943. 

712 Purpose of the Investigation 

In the first instance the research on concrete was 
undertaken to create a better quantitative basis for 
the design of defensive structures, as has just been 
discussed. As World War II progressed and the em¬ 
phasis shifted from defense to offense, many further 
implications of the knowledge gained began to appear. 
Basic knowledge concerning the terminal ballistics 
of concrete is needed in predicting the effects of our 
own weapons on the enemy’s fortifications, bunkers, 
submarine pens, and other concrete structures. It is 
extremely important to realize that an attacking bomb 
or projectile may be handicapped or even defeated by 

a Pertinent to War Department Projects CE-5 and CE-6 
and to Navy Department Project NO-32. 

b See Weapon Data Sheets 2A1, 2A3, 2A5, 2B1, 2C1, 2Cla 
of Chapter 19. 


such things as ricochet, deformation, rupture, im¬ 
proper fuzing, etc., and to avoid overestimation caused 
by a lack of understanding of the phenomena of ter¬ 
minal ballistics. Not only the advantageous choice and 
use of attacking weapons but also their design must 
be based on terminal-ballistic information. For ex¬ 
ample, the design of concrete-piercing projectiles and 
bombs to carry the maximum amount of high explo¬ 
sive without deformation and rupture against concrete 
requires estimating the nature and magnitude of the 
forces encountered during concrete penetration. Simi¬ 
larly, the best fuzing to detonate the projectile at 
maximum penetration or after perforation depends on 
the time of penetration or perforation; indeed, the 
question of fuze initiation also depends on a knowl¬ 
edge of the setback forces at impact, particularly in 
the case of very thin slabs. These examples and gen¬ 
eral remarks are perhaps sufficient to suggest the na¬ 
ture and relative importance of terminal-ballistic 
studies of concrete and their bearing on offensive as 
well as defensive activities. 

Beyond these particular applications the study of 
the terminal ballistics of concrete is of long-range 
importance because it sheds additional light on the 
general problems of penetration and perforation. Here¬ 
tofore only steel (including armor) had been studied 
extensively and perforation rather than penetration 
stood in the forefront of interest. This was partly be¬ 
cause of the difficulty in obtaining both the high ve¬ 
locities and the nondeforming projectiles required to 
produce massive penetrations beyond the nose height 
of the projectile. With concrete targets, ordinary pro¬ 
jectile velocities and ordinary armor-piercing [AP] 
projectiles are adequate to secure penetrations beyond 
the bourrelet in massive targets. Hence the simpler 
and more fundamental problem of massive penetra¬ 
tion could be studied extensively. Furthermore, the 
existence of a marked scale effect and the brittle 
rather than ductile nature of the target material serve 
to widen the range of phenomena considered in the 
theoretical treatment of penetration and perforation. 

713 History of the Problem 

It was probably surprising to everyone to discover 
that although extensive use of concrete had been made 
in fortifications and notably in the Maginot Line and 



I u\ l i 11KNTI Al .j 


191 








192 


TERMINAL BALLISTICS OF CONCRETE 


the West Wall, no evidence could be found in avail¬ 
able documents of any very serious experimental work 
on the terminal ballistics of concrete since the time of 
the Metz Committee, 1835. In view of the early period 
in which this work was done and the many uncertain¬ 
ties which surround it, it was concluded that a serious 
program should be entered into on the terminal ballis¬ 
tics of concrete. 

The history of the problem of the terminal ballistics 
of concrete before 1940 is adequately covered in a 
CPPAB report 2 discussing the theoretical and experi¬ 
mental results then available for the solution of the 
penetration problem in concrete, steel, wood, earth, 
and sand. This report surveys the theories of penetra¬ 
tion, the problem of rupture (scabbing), and of per¬ 
foration without rupture, and the effect on penetra¬ 
tion of the physical properties of the target. It also 
includes a substantial bibliography of those sources 
from which material was actually used in preparing 
the report, beginning with Robins in 1742 and con¬ 
cluding with British Air Raid Precaution [ARP] pub¬ 
lications of 1939. The principal authors cited include 
Robins, Euler, Morin, Poncelet, Piobert, Didion, 
Martin de Brettes, v. Wuich, Resal, Levi-Civita, Petry, 
deGiorgi, Cranz, Thompson, Scott, Peres, Milota, 
Gaede, Vieser, Heidinger, Skramtajew, Montigny, 
Speth, Bazant, Gailer, Ha rosy, and Hayes. 

714 Principal Contributions 

Both experimental and theoretical work was done 
on the terminal ballistics of concrete by Division 2 of 
NDRC and the afore-mentioned associated organiza¬ 
tions. Small- or model-scale experiments were carried 
out at Princeton, while large-scale tests were made at 
the Aberdeen Proving Ground, where the necessary 
facilities were made available by the Corps of Engi¬ 
neers and the Ordnance Department, U. S. Army. In 
compiling and reporting the experimental observa¬ 
tions, great emphasis was put on making complete 
and accurate tabulations of all principal and auxiliary 
data. The results have been found to be useful as 
source material for problems of many kinds and, it is 
hoped, may form the bases for better analyses of the 
phenomena of penetration and perforation in concrete 
than have yet been made. 

The course of the work during World War II may be 
outlined by the following brief summaries of the prin¬ 
cipal contributions. The bibliography for this chapter 
includes not only these references but also lists related 
work by the Army, Navy and by British organizations. 


1. Final Report, National Research Council, Com¬ 
mittee on Fortification Design, John E. Burchard, 
December 1944. 

While this is chronologically the last of the CPPAB 
and CFD reports, it is put first here because it con¬ 
tains a complete final review of the history, projects, 
and reports of these committees from their inception 
to the end. Work on the terminal ballistics of concrete 
formed part of the activity of these committees. 

2. Terminal Ballistics, II. P. Robertson, CPPAB 
Interim Report, January 1941. 

A critical survey of previous work in the field of 
penetration and perforation is given. The report con¬ 
tains extensive references to earlier work. 

3. Final Report for the gear eliding June 30, 1941, 
Part 1, CPPAB. 

This report contains the small-caliber penetration 
data of the first Princeton “Concrete Properties Sur¬ 
vey,” the object of which was to obtain experimental 
information on the effect of concrete properties on 
penetration resistance. The then current theories of 
concrete penetration are discussed and the data are 
analyzed in terms of the classical Poncelet theory. 
The first evidence suggesting the existence of the scale 
effect for concrete penetration is presented and dis¬ 
cussed on page 48 of this CPPAB report. 

4. Penetration of Projectiles in Concrete, Richard 
A. Beth, CPPAB Interim Report No. 3, November 
1941. 

This report suggests the use of an empirical penetra¬ 
tion formula for concrete of the form = KD V a d p , 
where z c is the nose-corrected penetration in cali¬ 
bers, D is the caliber density of the nondeforming 
projectile, V is the striking velocity, d is the caliber, 
and K, a, and /? are constants. The factor d 0 repre¬ 
sents the scale effect. 

5. AP Bomb Test — Comment, Richard A. Beth, 
CPPAB Interim Report No. 9, April 1942. 

Bibliography, data, and discussion of tests with 12- 
in. AP projectiles, weighing 1,000 lb, striking heavily 
reinforced concrete slabs of three thicknesses, 36, 60, 
and 81 in., at 1,000 fps and 20 degrees obliquity. The 
.45-caliber penetration data obtained on unreinforced 
1-ft cubes of the same concrete are also given and an 
attempt is made to evaluate the scale effect according 
to the type of formula suggested above. 4 This involves 
a suggested method of making allowance for the 
density of reinforcing steel on penetration. 


|o\i i lu-. vri u. $ 






INTRODUCTION 


193 


6. A Brief Summary of Recent Data on Penetration 
in Concrete at Various Scales, Richard A. Beth, 
CPPAB Interim Report No. 18, June 1942. 

A summary review of penetration data at .45-cali¬ 
ber, 37-, 75-, 155-mm, 12-, and 16-in. scales. The data 
are analyzed and correlated in terms of empirical 
formulas of the form suggested above. 4 Scale-elfect 
graphs are given. Some data on sticking, scabbing, and 
perforation of concrete by inert projectiles are given. 

7. Penetration and Explosion Tests on Concrete 
Slabs—Report I: Data, Richard A. Beth and J. 
Gordon Stipe, Jr., CPPAB Interim Report No. 20, 
January 1943. 

This report contains complete data and some pre¬ 
liminary analyses in the form of graphs of extensive 
tests on 39 reinforced concrete slabs at .45- and .50- 
caliber, 37- and 75-mm, 3-in., and 155-mm scales. 
Penetrations, perforations, obliquities, and explosions 
are included. 

8. Penetration and Explosion Tests on Concrete 
Slabs—Report II: Crater Profiles, J. Gordon 
Stipe, Jr., CPPAB Interim Report No. 21, Janu¬ 
ary 1943. 

Eleven large prints of measured crater profile draw¬ 
ings which are reproduced at smaller size in refer¬ 
ence 7. 

9. Resistance of Laminated Concrete Slabs to Perfora¬ 
tion, Robert J. Hansen, CPPAB Interim Memo¬ 
randum M-9, May 1943. 

Report on tests made at 37-mm scale to find the 
reduction in perforation limit velocity produced by 
pouring concrete slabs in successive layers rather than 
monolithically. A lowering of limit velocity by not 
more than 5 per cent per construction joint was found. 

10. Terminal Ballistics and Explosive Effects (Ap¬ 
pendix to the CPPAB Final Report for the year 
ending June 30, 19f3), CFD Report, Oct. 1943. 

This report contains a description of terminal- 
ballistic phenomena with concrete, steel, armor, and 
other target materials, together with a compilation 
of considerable quantitative information on these sub¬ 
jects in the form of tables, graphs, and nomograms. 
It was originally written to assist the Corps of Engi¬ 
neers in the preparation of a new fortifications 
manual. 

11. Concrete Properties Survey, Richard A. Beth, 
J. Gordon Stipe, Jr., M. E. DeReus, and J. T. 
Pittenger, CFD Interim Report 27, July 1944. 


This report consists of three separately bound 
parts: Effect of Concrete Properties on Penetration 
Resistance, Appendix A—Preparation and Physical 
Tests of Concrete, and Appendix B—Penetration Data. 

In order to explore the effect of various concrete 
properties on penetration resistance, 154 1-ft cube 
targets representing about 75 different concretes were 
made and tested for penetration resistance, using non¬ 
deforming hardened steel .50-caliber model-scale pro¬ 
jectiles. Tests were made at normal incidence with 
striking velocities from 600 to 2,000 fps. The earlier 
Concrete Properties Survey data 3 were neither so 
extensive nor so accurate as these newer data and 
should therefore be regarded as preliminary or aux¬ 
iliary to the data of this report. Summary tables of 
the data and a discussion and analysis of the results 
are contained in the first part of the report; the two 
appendices contain complete descriptions and original 
data on the parts of the work indicated by their titles. 

12. Ballistic Tests on Concrete Slabs, J. Gordon 
Stipe, Jr., M. E. DeReus, J. T. Pittenger, R. J. 
Hansen, CFD Interim Report 28, June 1944. 
(The separately bound Appendix A—Tables of 
Data contains full tabulations of all original bal¬ 
listic and concrete data.) 

Perforation, scabbing, and penetration tests were 
made on 133 concrete slabs in this companion pro¬ 
gram. 11 The same .50-caliber projectiles were used 
and slabs from 3 to 18 calibers thick were tested. 
These small-scale tests were planned to supplement 
the information at larger scales, 7 particularly with 
respect to the effect of slab thickness, concrete 
strength, aggregate gradation and size, various 
schemes of reinforcement, scab plates, and obliquity 
of incidence. The following relations were found: 
e/d = 1.23 -f- 1.072 and s/d = 2.28 -j- 1-132, 
where e/d and s/d represent the thickness that can 
be perforated and scabbed respectively, in calibers, 
and 2 is the penetration depth in calibers into massive 
concrete of the same characteristics at the perforation 
or scabbing-limit velocity. These relations show good 
agreement with the data except at obliquities above 
40 degrees. 

13. Repeated Fire and Edge Fire Effects on Small 
Concrete Slabs, J. Gordon Stipe, Jr., CFD 
Interim Memorandum M-12, July 1944. 

The number of rounds required for perforation of 
reinforced concrete slabs by repeated fire attack with 
.50-caliber model-scale projectiles was tested for two 


I ' >S ill' K VI I \t 






TERMINAL BALLISTICS OF CONCRETE 


194 


thicknesses of concrete, two reinforcing schemes, and 
for different distances from the slab edge. 13 Tables of 
ballistic data and many observed crater profile drawings 
are included. 

14. Composite Slabs, J. Gordon Stipe, Jr., CFD 
Interim Memorandum M-13, June 1944. 

A method of estimating the perforation-proof thick¬ 
ness of slabs composed of concrete and steel, soil and 
concrete, and of the three materials is proposed. 

15. Penetration Theory: Estimates of Velocity and 
Time during Penetration, R. A. Beth, OSRD-4720, 
NDRC Report OTB-7, February 1945. 

This paper summarizes the theory of the variation 
of the resisting force R during projectile penetration 
for three cases: (1) R is a constant (the Robins-Euler 
theory), (2) R is a function of the remaining veloc¬ 
ity v only (sectional pressure theories), and (3) R 
is a function of the penetration depth x only (sec¬ 
tional energy theories). The functional form of R 
is not known, but there are reasons for believing that 
the actual curve for R will fall between those pre¬ 
dicted for cases (2) and (3). A knowledge of R would 
be a step toward solving problems of fuze and pro¬ 
jectile design and the design of composite targets. 

16. Concrete Penetration, Richard A. Beth, OSRD- 
4856, NDRC Report A-319, March 20, 1945. 

An attempt is made to revive the Poncelet hypoth¬ 
esis by postulating a force law of the form R — 
a(x) -|- bv 2 for concrete penetration, and a(x) and 
b are evaluated from the .50-caliber penetration data 11 
and some additional data on the effect of projectile 
mass and nose shape given in an appendix. Calcula¬ 
tions of resisting force, time, and remaining velocity 
during penetration are made. The theoretical conse¬ 
quences of a further generalization of the Poncelet 
force law, R = a(x)v 2X -f- b(x) r 2 , in which the 
first term is able to take account of the concrete scale 
effect, are worked out in an appendix. 

17. An Electromagnetic Method for Measuring Pro¬ 
jectile Velocity during Penetration, R. A. Beth 
and E. J. Schaefer, OSRD-5175, NDRC Report 
A-329, June 1945. 

The method consists in magnetizing the projectile 
and recording the electromotive force induced in 
suitably disposed coils during deceleration in a non¬ 
magnetic and nonconducting target material, like 
concrete, by means of a cathode-ray oscillograph 
equipped with a linear time sweep. The report out¬ 


lines the theory and design of the coils, the equipment 
used, and describes preliminary experimental work 
including the methods of stablizing the magnetic 
moment of the projectiles against the effects of im¬ 
pact. 

18. Penetration Theory: Separable Force Laws and 
the Time of Penetration, Richard A. Beth, 
OSRD-5258, NDRC Report A-333, June 28, 1945. 

This report considers the consequences of assuming 
a separable force law of the form R = cg(x)f(v ) as 
an alternative to the generalized Poncelet force law. 16 
General formulas are given for penetration as a func¬ 
tion of striking velocity, remaining velocity as a func¬ 
tion of depth during penetration, and for time of 
penetration. A number of special cases are tabulated, 
including all of the classical theories of penetration. 
A separable force law for perforation leads to a rela¬ 
tion between limit, striking, and residual velocities 
of the form F(v t ) = F(v 0 ) — F(v r ), which is inde¬ 
pendent of the projectile mass and the target strength 
under certain plausible assumptions. 

19. Ballistic Tests on Concrete Slabs, II, Effect of 
Nose Shape, J. Gordon Stipe, Jr., OSRD-6638, 
NDRC Report A-112M. 

This report gives additional supplementary .50- 
caliber data of reference 12, particularly with respect 
to the effect of nose shape on scabbing and perforation. 

20. Final Report on Concrete Penetration, Richard 
A. Beth, OSRD-6459, NDRC Report A-388. 

This report summarizes the work on concrete pene¬ 
tration and perforation which has been done at Prince¬ 
ton during "World "War II. It then proposes an ap¬ 
proximate theory of concrete penetration which cor¬ 
responds to the present state of knowledge on the 
subject. 

7.2 PHYSICAL DESCRIPTION OF 

PHENOMENA 

Some of the principal phenomena resulting from 
the impact of inert nondeforming projectiles on re¬ 
inforced concrete slabs are illustrated in Figures 1 
and 2. Each drawing represents a section through the 
slab in the plane of incidence of the projectile (see 
Figure 3, Chapter 5) and is drawn to scale from mea¬ 
surements of an actual shot. They are arranged to 
show the effects of slab thickness, striking velocity, 
and obliquity. The data were obtained in the penetra- 


C '' \ I i ! 'KNT i A1 











PHYSICAL DESCRIPTION OF PHENOMENA 


195 


tion and explosion tests on concrete slabs 7 and are 
displayed in somewhat different form in Data Sheet 
2A3, Chapter 19. 

Figures 1 and 2 are based on observations made 
with 37-mm AP projectiles, with cap and windshield 
removed. The projectile weight was about 1.70 lb, 
which gives a caliber density D of 0.554 lb per cu in. 

7 - 2 * 1 Scale Effect 

Qualitatively similar results have been observed 
with projectiles of various calibers from 0.30 to 16 in. 
and with AP and semi-armor piercing [SAP] bombs. 
Quantitatively, however, because of the scale effect 


in concrete, the effects illustrated are produced at pro¬ 
gressively somewhat lower striking velocities as the 
caliber or scale is increased for projectiles of the same 
form and caliber density and for targets of the same 
concrete composition, strength, age, and thickness in 
calibers. These scale effect results invalidate the rule 
of thumb resulting from earlier theories that under 
similar circumstances penetration is proportional to> 
caliber. For large changes in caliber this effect can 
be a serious one. In round figures the massive penetra¬ 
tion measured in calibers for large projectiles is 100 
per cent greater than that for small projectiles in 
going from .50 caliber to 16 in., and 50 per cent 




0 0.5 I 2 FEET RIC = RICOCHET 


Figure 1. Thin slab. Profiles of actual craters. Slab: thickness, 8.9 in.; compressive strength, 5,700 psi. Projectile: 37-mm 
M80; weight, 1.70 lb; cap and windshield removed. Striking velocity (fps) shown for each impact. 





























































































































196 


TERMINAL BALLISTICS OF CONCRETE 


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Figure 2. Thick slab. Profiles of actual craters. Slab: thickness, 22 in.; compressive strength, 5,700 psi. Projectile: 37-mm 
M80; weight, 1.70 lb; cap and windshield removed. Striking velocity (fps) shown for each impact. Stuck projectiles 
actually shown. 


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PHYSICAL DESCRIPTION OF PHENOMENA 


197 


greater in going from 1- to 6-in. calibers, for other¬ 
wise similar circumstances. 

Being made from observations on actual shots, 
Figures 1 and 2 show not only the general trends 
found by varying striking velocity and obliquity for 
two typical thicknesses of slab, but also exhibit the 
kinds of random variations from an idealized norm 
which are found even under well-controlled condi¬ 
tions. It is convenient to make an arbitrary division 
into front- and back-face phenomena for the purposes 
of discussion. 



CAL. .50 2“ X 2” GRID 


7,2,2 Front-Face Phenomena 

Front Crater; Spalling 

Pieces of concrete, called spalls, are ejected from 
the region surrounding the point of impact thus leav¬ 
ing the front crater seen in the drawings. The size of 
the crater formed increases rapidly with increasing 
striking velocity up to 1,200 or 1,500 fps for ordinary 
AP projectiles and less rapidly at still higher strik¬ 
ing velocities. Its shape is roughly conical but very 
irregular. The presence of a reinforcing layer or mat 



37 MM 6" X6 m GRID- 



75 MM 


6“X6" GRID 155 MM 


6" X6“ GRID 


Figure 3. Spall craters in concrete due to AP projectiles striking normally at approximately 1,050 fps. All photographs 
to same scale in calibers. Cord grids placed in front of craters show original size. 













































198 


TERMINAL BALLISTICS OF CONCRETE 


near the front face tends to have a constricting effect 
on both the size and shape of the crater. The photo¬ 
graphs of Figure 3 show the appearance of typical 
front-face craters at different scales. Those illustrated 
were produced by the impact of .50-caliber, 37-, 75-, 
and 155-mm projectiles, respectively. The photo¬ 
graphs have been reproduced at different scales so 
that the projectile diameters have the same absolute 
size for all of the photographs. 

Penetration 

For a given missile and target the average normal 
penetration may be expected to increase with striking 
velocity according to a smooth curve. Actually the 
random variations of individual shots from the ideal 
mean curve may be as great as 10 or more per cent in 
penetration. In Section 7.3.3 the mathematical repre¬ 
sentation of the penetration curve will be discussed for 
"massive” targets, that is, targets so thick that the 
concrete does not begin to yield (scab) on the back 
face. When scabbing (see next section) sets in, pene¬ 
trations begin to increase more rapidly with striking 
velocity than indicated by the curve for massive pene- 
t rati on. 

At striking velocities up to about 1,000 fps a nor¬ 
mally incident projectile does not penetrate beyond 
the crater which it forms, and the deepest point of 
the nose impression appears roughly as the apex of 
the sloping crater sides. At higher velocities a non¬ 
deforming projectile begins to form a cylindrical 
penetration hole beyond the crater, provided the tar¬ 
get is thick enough. This is illustrated particularly in 
the crater profiles on the left side of Figure 2. 

Obliquity tends to reduce the penetration depth as 
measured perpendicular to the target face although 
the slanting or curved path length of the projectile 
in the target may be almost the same as in the case 
of normal incidence. With ricochet (see below) this 
path length may be even greater than for the normal 
case. For practical purposes, however, the depth 
reached below the face of the target seems more sig¬ 
nificant than the slant depth. The drawings show that 
this perpendicular depth decreases in a regular way 
with increasing obliquity, although the random varia¬ 
tions of individual shots from an idealized average 
curve have been found to be even larger than in the 
previously discussed case of normal penetration. This, 
together with the fact that relatively much fewer ex¬ 
perimental data are available and the fact that it is 
expected that the perpendicular penetrations at vari¬ 
ous obliquities depend on both nose shape and pro¬ 


jectile length in a complicated way, has made it much 
more difficult to establish general rules or formulas 
for penetrations at obliquities. 

Sticking 

In a thick slab, if the penetration hole goes deep 
enough beyond the front crater, the projectile is likely 
to stick, that is, be held tightly at or near its maxi¬ 
mum penetration without falling out of the penetra¬ 
tion hole or rebounding from the target. Experience 
indicates that a projectile must penetrate at least 3.5 
to 4.5 calibers before it will stick, the larger factors 
apparently being required for thicker slabs. Such 
penetrations will ordinarily be attained at normal in¬ 
cidence with striking velocities in the region between 
1,000 and 2,000 fps, the value depending on the actual 
weight and caliber of the nondeforming part of the 
projectile, the strength and penetration resistance of 
the concrete, and the thickness of the slab. The veloc¬ 
ity at which sticking sets in with a given projectile- 
target combination is called the sticking limit. The 
sticking limit increases with increasing obliquity. A 
number of cases of sticking are shown in the upper 
two rows of Figure 2. 

The phenomenon of sticking is of special impor¬ 
tance with explosive jirojectiles or bombs. It is felt 
that the maximum effect of detonation is secured when 
explosion takes place at the deepest penetration that 
can be attained by the inert missile before detonation. 
It is practically impossible to fuze accurately enough 
for this if the projectile rebounds. In general the fuze 
time should be made long enough to allow perfora¬ 
tion or the maximum penetration to be reached be¬ 
fore the missile detonates. If the fuze setting is greater 
than the time required for either perforation or maxi¬ 
mum penetration, the maximum damage will be se¬ 
cured except in the case of rebound, while if the fuze 
setting is shorter the projectile will be definitely han¬ 
dicapped with respect to the target in almost all cases. 
The mass and striking velocity of bombs are usually 
too low for sticking penetration; if the target is too 
thick to be perforated, a bomb will rebound instead 
of sticking. 

Ricochet 

Examples of ricochet may be seen in the lower 
right half of each of the Figures 1 and 2. Ricochet 
will occur for a given striking velocity when the ob¬ 
liquity becomes great enough. Conversely, for a fixed 
obliquity or angle of incidence different from normal 
there is a limiting velocity, the ricochet limit, below 





PHYSICAL DESCRIPTION OF PHENOMENA 


199 


which ricochet occurs and above which the projectile 
digs into the slab without ricochet. It will be noted 
that the ricochet limit increases sharply with obliquity. 

Ricochet greatly handicaps the missile with respect 
to the target and thereby enhances the protection 
afforded by the slab while decreasing the relative ef¬ 
fectiveness of the projectile. This applies particularly 
to explosive projectiles or bombs when the fuze set¬ 
ting is such that the detonation takes place when the 
missile is no longer in contact with the target. The 
lateral and turning forces exerted on the projectile or 
bomb during ricochet also pose difficult problems for 
the fuze designer. 

Although perforation and ricochet cannot, by defi¬ 
nition, occur simultaneously, it is possible to have a 
scab thrown off from the back of the slab when the 
projectile ricochets. With sufficiently thin slabs the 
front and back craters so formed have been observed 
to overlap in such a way as to leave a clear hole 
through the slab, even though the projectile remains 
on the attacking side of the slab and therefore does 
not perforate in the true sense. 

7 2 3 Back-Face Phenomena 

Back Crater ; Scabbing 

For a given target slab a progressive increase of 
striking velocity produces, first, cracking on the back 
surface, followed by scabbing of increasing extent. 
Scabbing consists of the ejection of pieces of concrete 
from the back of the slab opposite to the impact point 
thus leaving a back crater after the shot. The lowest 
velocity for which scabbing will occur is called the 
scab limit for any particular missile-target combina¬ 
tion. The scab limit increases slowly with obliquity 
for angles up to 10 or 15 degrees and more rapidly 
for larger angles. 

Figure 4 shows the appearance of typical back-face 
craters at various scales, namely .50-caliber, 37-, 75-, 
and 155-mrn. As with the front-face craters shown in 
Figure 3, the photographs have been reproduced to 
the same scale in calibers. The back-scab crater is 
usually wider and shallower than the front-spall 
crater, although both tend to be very irregular and 
to show large departures from symmetry, smoothness, 
and reproducibility. In reinforced concrete often only 
the cover (the concrete layer outside or beyond the 
back-face reinforcing mat) is actually projected away 
from the slab, while a considerable amount of badly 
broken and cracked target material may be retained 
within the reinforcing mat. On the other hand, as 
may be seen in Figure 4, the back mat tends to widen 


the area of cover which is loosened and thrown off, 
especially when insufficient shear steel is provided for 
tying each lateral bar to the body of the slab at closely 
spaced intervals. 

Below the scab limit a concrete slab or wall will 
offer adequate protection to personnel or equipment 
not in direct contact with the slab and therefore not 
directly subjected to whatever mechanical shock may 
be transmitted through it. However, as soon as scab¬ 
bing sets in, pieces of considerable size and velocity 
may be thrown off. Thus scabbing is the first serious 
source of danger to the objects which the slab is in¬ 
tended to protect. In this light the scab limit rather 
than the perforation limit is often used as the prin¬ 
cipal criterion in the design of protective concrete. 

Perforation 

The perforation limit is the lowest velocity at 
which the projectile or bomb just passes completely 
through the slab. Like the scab limit it is lowest for 
normal incidence and it increases with obliquity in a 
roughly similar way. Beginning at the scab limit, 
penetrations increase more rapidly with striking ve¬ 
locity than in massive concrete, the excess being 
largest just before perforation is attained. Hence the 
perforation limit is found to be markedly lower than 
the velocity required to penetrate a distance equal 
to the slab thickness in massive concrete of the same 
characteristics. 

Perforation is especially dangerous in the case of 
explosive projectiles and bombs that are fuzed to de¬ 
tonate after perforation. The missile may be expected 
to produce the maximum damage to personnel and 
equipment when this explosion, fragmentation, and 
blast take place within a space entirely enclosed, and 
supposedly protected, by concrete walls and roof. The 
residual velocity of a projectile, after perforating such 
an enclosure, is usually insufficient to carry the pro¬ 
jectile through the far wall and out again even if the 
direction of the trajectory is favorable; therefore the 
fuze time need only be made sufficiently long to 
secure maximum damage. 

Limit Velocities 

It should be emphasized that the limit velocities 
for scabbing and perforation as they have been de¬ 
fined here are idealized mean values at which the 
missile will just begin to scab or to perforate the 
concrete slab in question. Actually the values are not 
sharp; repeated tests under well-controlled conditions 
show the same kind of random fluctuations as have 









200 


TERMINAL BALLISTICS OF CONCRETE 




CAL .50 


2“ X 2" GRID 37 MM 


6*' X 6" GRID 



75 MM 6" X6“ GRID 155 MM 6" XG" GRID 


Figure 4. Scab craters in concrete due to AP projectiles striking normally at velocities slightly above perforation limit. 
All photographs to same scale in calibers. Cord grids placed in front of craters show original size. 


been mentioned in connection with the other concrete 
phenomena. (Compare with Chapter 8.) In practice 
it is necessary to allow for these uncertainties by using 
an appropriate “safety factor” or “ignorance factor” 
to ensure that scabbing or perforation either will or 
will not take place accordingly as the purpose is 
attack or defense. 

Limit Thicknesses 

It is often convenient, in dealing with these phe¬ 
nomena for design purposes, to consider the striking 
velocity fixed and to ask for the slab thickness that 
will just be scabbed or just be perforated. Here again 


the terms scab-limit thickness and perforation-limit 
thickness are used for the idealized mean thicknesses 
without allowance for uncertainties. 

7 - 2,4 Important Characteristics of 

Concrete Targets 

The terminal-ballistic behavior of a concrete tar¬ 
get depends on the nature and quality of the concrete 
and on certain construction features such as size, re¬ 
inforcement, etc. This is well illustrated by some of 
the phenomena already described and shown in Fig¬ 
ures 1, 2, 3, and 4. A deeper understanding of these 
as well as some of the other phenomena to be dis- 





































PHYSICAL DESCRIPTION OF PHENOMENA 


201 


cussed may be gained by reviewing some of the more 
important and typical characteristics of concrete 
targets. 

Thickness and Quality of Concrete 

Some idea of the order of size of the concrete tar¬ 
gets under discussion may be gained from the fact that 
practically all of the experimental work has been 
done on slabs whose thickness falls somewhere in the 
range from 3 to IS calibers. The perforation thickness 
of good reinforced concrete (say, 5,000-psi cylinder 
strength) for normally incident AT projectiles at 
2,000 fps may, because of the scale effect (see Sec¬ 
tion 7.2.1), be as low as 9 to 12 calibers for .50-cal¬ 
iber 12 and run as high as 16 to 18 calibers for 
16-in. 21 projectiles. These statements are merely in¬ 
tended as a guide to the order of magnitude of the 
thicknesses under discussion; whenever possible the 
actual design of protective structures, estimates of 
weapon performance, or other theoretical work should 
be based on a more detailed consideration of the fac¬ 
tors involved. 

One of these factors is the quality of the concrete. 
In general, the selection of materials, mix design, 
methods of placing, etc., which govern the quality 
of concrete for civil construction have a similar effect 
on the ability of concrete to resist the effects of pro¬ 
jectile impact. Extensive experimental tests at .50- 
caliber 11 and smaller scales 3 were made during World 
War II to study the effect of concrete properties on 
penetration resistance. Many suggestive correlations 
appear in the data but, as may be expected, it is 
difficult to find a general quantitative formulation 
for them. 

A case in point is the effect on penetration of 
changes in compressive strength. This is important 
because compressive strength is perhaps the most com¬ 
mon engineering designation of the quality of con¬ 
crete. The small-caliber tests, confirmed by some evi¬ 
dence at larger scales, suggest the following approxi¬ 
mate rule of thumb : 23 for a given projectile and 
striking velocity the normal depth of penetration is 
inversely proportional to the square root of the com¬ 
pressive strength of the concrete. For example, an in¬ 
crease of 10 per cent in compressive strength will 
reduce penetrations by about 5 per cent under other¬ 
wise similar circumstances. This rough rule seems to 
hold whenever the kind, amount, and size distribution 
of the aggregate component remains essentially un¬ 
changed, and the increase in compressive strength is 
secured by an increase in the cement content of the 


mix or by an increase in the age of the target tested. 
But an exception has been found with differences in 
strength occasioned by different curing conditions. 11 
Compared to otherwise similar moist-cured concrete, 
dry-cured targets showed up to 20 per cent increase 
of penetration resistance while the nominal compres¬ 
sive strength, measured on companion cylinders cured 
with each target, decreased by 40 to 50 per cent. 

The experimental tests also show that penetration 
is affected by changes in the aggregate component of 
the concrete in the sense that an increase in the size 
and amount of aggregate put into the concrete tends 
to decrease penetrations. But it is not clear what ag¬ 
gregate parameter would be most appropriate for a 
quantitative formulation of this effect, especially when 
differences in scale or caliber have to be considered. 

The .50-caliber tests on several dozen targets 11 in¬ 
dicate the order of magnitude of the effect to be as 
follows: with concretes up to 4,000-psi compressive 
strength, penetrations decreased by about 20 per cent 
when the aggregate was changed from fineness modu¬ 
lus 3.0, %-in. maximum size, and 65 per cent by 
volume, to fineness modulus 5.0, 1-in. maximum size, 
and 75 per cent by volume. For 7,000-psi concrete 
the effect seems to be smaller. 

Even among the three specific aggregate parameters 
named it is hard to decide, on the basis of experi¬ 
mental data, which is the most appropriate for de¬ 
scribing the effect. Concrete technologists insist that 
a reasonably smooth gradation of aggregate sizes, from 
coarse stones and gravel down to fine sand, must be 
used in making good concrete. The water-cement ratio 
determines the compressive strength of the resulting 
concrete, independent of the amount and sizes of 
aggregate used. For a given water-cement ratio, an 
amount of water-cement paste somewhat in excess of 
that needed just to fill the voids in the dry aggregate 
is usually provided. Less paste will obviously result in 
porous concrete and too great an excess may result in 
nonuniformity, a tendency toward segregation, and an 
unwarranted increase in cost. An increase in the ag¬ 
gregate size, which tends to decrease the proportion¬ 
ate volume of the interstitial spaces (since a smooth 
gradation down to the finest sand is still required), 
also tends to decrease the water-cement paste required, 
and thereby tends to increase the percentage by vol¬ 
ume of solid aggregate in the resulting concrete. A 
consequent difficulty is the impossibility of making 
accurately scaled-down concrete for model tests in 
which the relative volumes of aggregate and paste are 







202 


TERMINAL BALLISTICS OF CONCRETE 


maintained. 11,22,48 Furthermore, a proper adjust¬ 
ment of the gradation and the amount of water- 
cement paste requires a certain degree of correlation 
without, however, compelling a unique relationship 
to exist among the three aggregate parameters named 
above. Obviously the same would be true for any other 
aggregate parameter which might be devised. This 
is the reason for the difficulty in obtaining a clear 
experimental indication of the appropriate aggregate 
parameter affecting penetration, namely, it is not pos¬ 
sible to vary any one over a very wide range and still 
maintain the others constant. Some progress might 
be made by using statistical methods, but sufficient 
data for this are not now available. 

Theoretical considerations have not given a clear 
solution of the aggregate problem either. Energy con¬ 
siderations suggest that the proportionate volume of 
aggregate in the concrete should play a role, since the 
energy required per unit volume to crush a stone ag¬ 
gregate of good quality is undoubtedly greater than 
that required to crush a unit volume of the interstitial 
mortar. Since compressive strength is mainly a mea¬ 
sure of the quality of the interstitial cement, the 
above-mentioned experimental observation that the 
effect of aggregate changes seems to be less with 
concretes of high compressive strength tends to sup¬ 
port the crushing energy considerations just described. 
Some English interpretations of concrete penetration 
data 22,48 suggest that the aggregate effect and the 
scale effect (see Section 7.2.1) arise from the same 
cause and that penetration is, in fact, a function of 
the dimensionless ratio of caliber to (maximum) ag¬ 
gregate size. It may be possible to reconcile this inter¬ 
pretation with the energy consideration discussed 
above by assuming that the degree of crushing of 
aggregate, and hence the energy required, is in some 
way a joint function of aggregate and projectile size. 
On this basis the scale effect also should be less pro¬ 
nounced with concretes of high compressive strength 
and greater with weak concretes. This has not yet 
been observed, but it is doubtful whether the available 
data are adequate to show the effect if it does exist. 

The material of which the aggregate is composed 
can have some influence on penetration resistance, as 
shown by small-caliber tests, 11 but no quantitative 
laws connecting this effect with physical properties 
of the aggregate material have as yet been found. 

On the other hand, tests of special cements or ad¬ 
mixtures have so far shown no significant improve¬ 
ment in the penetration resistance of the resulting 
concrete in relation to the compressive strength. Usu¬ 


ally, if the same trouble and expense were applied in 
making a richer mix or in making the slab thicker, a 
much greater increase in protection would be secured. 

As far as protective construction (fortifications, 
bomb shelters, etc.) is concerned, the net result of the 
small-caliber tests is as follows: Taking for granted 
that modern methods of mix design and field pro¬ 
cedures in handling and placing are used and that 
a clean, hard aggregate (e.g., quartz or traprock, etc.) 
can be selected, it is advantageous to use as large a 
fineness modulus and as large a proportionate volume 
of aggregate as possible in the concrete. The maxi¬ 
mum aggregate size chosen will, of course, be limited 
in the usual way by the availability of a reasonably 
good gradation below the maximum, the spacing of 
the reinforcing bars, and the thickness of the section 
to be poured. The change of compressive strength, and 
hence of penetration resistance, with water-cement 
ratio was found, approximately, to be such that for 
a given amount of cement about the same protection 
against perforation can be secured whether a thick 
slab with high water-cement ratio and weak concrete 
or a thinner slab with low water-cement ratio and 
strong concrete is made. 11 

Reinforcement 

As a material, concrete is much stronger in com¬ 
pression than it is in tension. When overstressed by 
static loading it fails in a brittle rather than in a 
ductile manner. Under the impact of bombs and pro¬ 
jectiles it exhibits the same general characteristics, 
which are quite different, by and large, from the 
toughness and ductility shown by most metals. 

When a massive concrete slab suffers a direct hit 
the penetrating missile crushes the concrete ahead of 
it and tends to drive the detritus forward and side- 
wise. During deep penetrations most of this crushed 
material is ultimately driven aside because of the re¬ 
action of the compressed and confined material ahead 
of the missile and because of the pointed nose shape 
of bombs and projectiles. This sets up strong radial 
pressures and circumferential tensions around the 
penetration hole which result in pronounced radial 
cracking because of the weakness of the concrete in 
tension. The forces are easily able to crack up quite 
large masses of concrete unless sufficient reinforcing 
steel is present to inhibit the spreading of the cracks 
and to offer tensile strength bridging the cracks that 
are formed. With inadequate reinforcing, the struc¬ 
tural collapse following the cracking due to a single 
shot may breach a wall or roof completely. 







PHYSICAL DESCRIPTION OF PHENOMENA 


203 


Thus the principal function of steel reinforcement 
in concrete protective structures is to inhibit mass 
cracking, as well as splintering, scabbing, and spalling 
(see below), which result from a direct hit or explo¬ 
sion, and to supply structural, tensile, or flexural 
strength. The effect of reinforcing steel in resisting 
penetration along the path of the projectile in con¬ 
crete is too small to warrant any large increase in 
percentage of steel or in complication of the reinforce¬ 
ment pattern for this purpose. 5 See also Section 15.2.5 
of Chapter 15, where impact tests on reinforced con¬ 
crete beams are discussed. 

For protective construction it is felt that reinforc¬ 
ing steel need not exceed about one percent of the 


of weakness along which the concrete tends to crack 
and separate as a result of impact or shock. The latter 
tendency was found to be particularly severe when 
sheets of expanded metal were tried as reinforcing in 
burster slab tests. 

Some typical reinforcement patterns are shown in 
Figure 5. The concrete cover over the face mats should 
be as thin as practicable in order to reduce spalling 
and scabbing as much as possible. Figure 6 shows the 
effect of front-cover thickness on spall formation in 
the case of some 75-mm tests. The striking velocity for 
the upper two photographs was about 1,900 fps, and 
about 1,400 fps for the lower two. Spalling of the front 
cover is also shown in Figure 3. Similarly Figure 4 


TOP OR FRONT FACE 



TOP OR FRONT FACE 


TOP OR FRONT FACE 


. 


o 

_ i > 
<0 


-h —H—ri—rf—H~ 

u i H i \i 


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"ir 

_ 5/8"0 i6"oc eawoy 

I ^V2"0 stirrups 8"o c s 
staggered ; every 3rd & 
stirrup in each row -_L 
continued through 


I ! 


I ! 


-if ~h—! i —ij—jh 

i 


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CD 


. 4 - 

V) 




I I 
I I 


I I 


li 


H- 


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+- 


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l/2"0 6"o c eawoy 
l/2"0 9"oc eawoy 


A 


1/2" 0 16" oc eawoy 


1/2" 0 16" oc eawoy = 


X, 




O 

B I 

CVJ 


5/8"0 8" oc ea woy 


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i 

H* 

i i 
i i 


. l/2'.'0 !2"oc eawoy L 


I 


5/8“0 8" oc eawoy 


CD 

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HfiUbi-w 

5/8"0 8"oceaway s 4 a 


l/2"0 stirrups 6"oc 
staggered ;every 3rd 
st|rrup in each row 
continued through 


l/2"0 9"oc eawoy 


l/2"0 6" oc eawoy 
l/2"0 6"oc eawoy 


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5 layers 
l"° l5"oc 
ea way 


I 


BOTTOM OR REAR FACE 

APPROVED METHOD 


BOTTOM OR REAR FACE 

APPROVED METHOD 


- 

BOTTOM OR REAR FACE 

NOT APPROVED 


Figure 5. Methods of reinforcing 6-ft protective wall or roof slab. (From Fortifications, Mines and Demolitions Branch, 
Office of the Chief of Engineers.) 


total volume of the concrete and that deformed bars 
should be used if available. Small bars with close 
spacing are somewhat preferable to large bars with 
wide spacing, but the choice should also take into 
account practical considerations such as the relative 
difficulty of bending and placing the steel. The ad¬ 
vantage to be secured by the use of large maximum¬ 
sized aggregate has been mentioned, and the spacing 
of reinforcing bars should not be so small as to make 
the proper placing and consolidation of the concrete 
difficult. While closer spacing tends to reduce the 
width and extent of cracks which intersect the plane 
of the reinforcing, it must also be remembered that 
very close spacing has been observed to create planes 


shows the way in which the scab formed from the back 
cover is thrown away from the slab while a great deal 
of the broken-up scab material formed within the re¬ 
inforcing is retained by the back-face mat. Figure 4 
also illustrates how the back-face reinforcing acts to 
extend the area of scabbing along the plane of weak¬ 
ness formed by the mat. It is therefore particularly 
important to reduce the thickness of the back cover 
in protective construction. (See discussion of scab 
plates and meshes below.) 

Besides restricting the size of front and back craters 
and increasing the resistance to repeated hits by hold¬ 
ing broken-up concrete in place, the face mats also 
serve their usual structural purpose in providing flex- 


















































204 


TERMINAL BALLISTICS OF CONCRETE 




COVER 2.2" 


COVER 6.0" 




Figure 6. Effect of cover on front-face crater formation. The upper photographs are at higher velocity. 


ural strength for the slab. A slab tends to recoil and 
vibrate after impact, so that tensile reinforcing is 
needed in the front face as well as in the back face. 

In protective construction more internal reinforc¬ 
ing is used than in civil construction. Shear steel is 
required to tie the face mats to the body of the slab at 
frequent intervals in order to promote their anticra¬ 
tering functions as described above; an effective sys¬ 
tem is to tie the face mats together by shear steel run¬ 
ning through the whole thickness of the slab. Addi¬ 
tional reinforcing mats similar to the face mats and 
parallel to them are provided in the interior of the 


slab as shown in Figure 5. These supply tensile 
strength to resist the cracking occasioned by the pene¬ 
tration forces previously described, and are particu¬ 
larly valuable in holding cracked or broken concrete 
in place to resist repeated fire (however, see Section 
7.2.7). In American practice these interior mats are 
usually somewhat more closely spaced near the sur¬ 
faces of the slab (see Figure 5), while an equal spac¬ 
ing is sometimes advocated in England. 

Scab Plates and Meshes 

Steel plates are often attached to the back face of 
concrete slabs, particularly roofs, to inhibit scab ejec- 























PHYSICAL DESCRIPTION OF PHENOMENA 


tion and to retain scab material in the case of direct 
hit. In order to function properly such scabbing plates 
must be attached by strongly welded lugs or heavy 
bolts at frequent intervals as shown in Figure 7. Spot 
welding to the shear steel has been found to be inade¬ 
quate. 7 Tests have shown the shock of a deep pene¬ 
tration to be sufficient to break such welds over a wide 
area; the result can be worse than having no scab plate 
at all if the plate itself is thus added to the ejected 

PROPERLY TIED SCAB PLATES 


205 

of a burster slab is increased by this backing over what 
it would be as an unbacked roof slab. 

In small-scale tests a scab mesh embedded in the 
back surface of the slab has given excellent results in 
retaining scab material from contact explosions on the 
front side of the slab. 54 The mesh was placed in con¬ 
tact with the form for the back-slab face and was tied 
to the internal reinforcing structure. In permanent 
construction it would be necessary to use bituminous 

IMPROPERLY TIED SCAB PLATES 


CONSTRUCTION 



FIRM EMBEDMENT OF ANCHORS & PL’ATEj 
STRONG JOINTS 



INSUFFICIENT EMBEDMENT OF ANCHOR 
a PLATE 




scab plate 
WEAK JOINT 


reinforcing 
pot weld 

BETWEEN PLATE 
AND ANCHOR 


BEHAVIOR 



concrete scab. Besides being firmly attached, the scab 
plate should be made in one continuous sheet if pos¬ 
sible (or securely welded together at the seams of ad¬ 
joining sheets), with the edges embedded in the sup¬ 
ports as suggested in Figure 7. 

It is believed that a well-designed scab plate will 
add from 5 to 10 per cent to the scabbing and perfora¬ 
tion resistance of a concrete slab. In the case of a 

* 

burster slab the earth on which it rests forms a back¬ 
ing. There is evidence that the perforation resistance 


paint or other means to prevent the exposed portions 
of this mesh from being weakened by rust. In effect, 
the idea behind the scab mesh is to prevent the dam¬ 
age that may be caused by flying scab pieces by reduc¬ 
ing the thickness of the back cover to zero (see the 
discussion of Figure 4 above). It should be emphas- 
sized that more extensive and larger scale tests of the 
scab mesh idea are needed before it can be either re¬ 
commended or discarded as far as full-scale protective 
construction is concerned. 


COmiLiraTIALj 

































































206 


TERMINAL BALLISTICS OF CONCRETE 


Layers and Laminations 

If a thick slab is constructed in several layers or 
laminae its resistance to perforation tends to be less 
than for a monolithically poured slab of the same di¬ 
mensions and quality. On the basis of 37-mm tests 
with a total slab thickness of 1 foot, it is estimated 
that the perforation limit velocity will be lowered by 
not more than 5 per cent per construction joint. 9 The 
outer layers should be at least 2 to 3 calibers thick and 
reasonable care should be taken to secure good me¬ 
chanical contact between the layers by cleaning and 
washing off the surface with water before each new 
layer is poured. 

In new construction, pouring in layers or lifts may 
be justified for several reasons in spite of the indi¬ 
cated decrease of efficiency in the concrete used. Limi¬ 
tations of equipment and length of working shift may 
make monolithic pouring impractical. With very thick 
slabs it may even be a net advantage to pour the mass 
in sections with sufficient time between pours for set¬ 
ting and cooling, because the heat generated during 
setting may cause mass temperature strains and crack¬ 
ing with a resulting impairment of penetration resis¬ 
tance. 21 With old construction it is sometimes desired 
to increase the thickness and protective value of exist¬ 
ing walls, roofs, or burster slabs by adding a layer of 
new concrete. 

For design purposes with either old or new con¬ 
struction, it is suggested that, assuming clean contact 
between layers, the above-mentioned allowance of 5 
per cent in limit velocity per construction joint will 
be found to be on the safe side. 

Spaced Slabs 

Model-scale tests have shown that a double slab 
construction with an air space between the slabs may 
actually be more resistant to scabbing, perforation, 
and contact explosions than the same amount of con¬ 
crete poured as a single slab. 54 In .50-caliber tests a 
double slab system, consisting of a 6-in. front slab 
separated by a %-in. air space from a 1-in. back slab, 
was slightly more resistant than a single slab 7 in. 
thick. The combination of a 3- and a 1-in. slab with 
a %- in. air gap had approximately the same resis¬ 
tance to perforation or scabbing as a single slab 4 in. 
thick. The combination of a 3- and a 1-in. slab with 
no air gap was less resistant than a single slab 4 in. 
thick, in agreement with the 37-mm laminated slab 
results mentioned above. 

It was originally expected that the scabbing of the 
first slab into the air space between the two slabs 


would result in a net decrease in the scabbing and per¬ 
foration resistance of the combination. The anomalous 
fact that this decrease in resistance usually does not 
take place appears to be due to the fact that the pro¬ 
jectile perforating the first slab with a low residual 
velocity tends to tumble in the air space between slabs 
and strike the second slab with large yaw. 

The spaced slab construction appears to be very 
promising on the basis of the model-scale tests, but, 
as in the case of the scab meshes discussed above, more 
extensive and larger-scale tests are needed to decide 
the real merits of the idea. 

Composite Slabs 

Some preliminary work has been done on the prob¬ 
lem of designing composite slabs of concrete and steel, 
or of soil and concrete, to resist perforation by inert 
projectiles. 

The simplest method consists of the following em¬ 
pirical procedure. 14 It is assumed that the limit thick¬ 
ness or proof thickness for each of two materials at 
the required limit velocity is known. The composite 
slab of this limit velocity will consist of a fraction a 
of the proof thickness of the first material in contact 
with a fraction b of the proof thickness of the second 
material. A graph is made by plotting a against b. 
The required values of a and b should lie on a smooth 
curve whose end points on the axes are fixed because, 
by definition, a = 1.00 when b — 0, and a — 0 when b 
= 1.00, and the curve should be such that a decreases 
monotonically as b increases and vice versa. In gen¬ 
eral, the curve may be expected to lie in the vicinity 
of the straight line a -f- b = 1.00. 

A plot of some .50-caliber data for combinations of 
concrete and steel suggests that these curves may be 
practically the same no matter for what particular 
limit velocity they are made, and an approximate mean 
curve has been given. For similar .50-caliber data on 
soil and concrete, it was felt to be more appropriate to 
express the a for soil as a fraction of the mean penetra¬ 
tion distance in soil for the limit velocity. Then the a 
versus b curves showed a falling trend with increase in 
limit velocity such that the curve falls above or below 
the straight line a -f- b = 1.00 by varying amounts, 
according as the limit velocity is below or above about 
1,400 fps. A more complete investigation, including 
data for larger calibers, should be made. 

A second method of designing composite slabs has 
been suggested, based on making estimates of the re¬ 
maining velocity of the projectile as it reaches each 

laver of different material after the first. 15 This re- 

«/ 


■HentiaiA 







PHYSICAL DESCRIPTION OF PHENOMENA 


207 


quires having an adequate knowledge of the variation 
of velocity as a function of depth during penetration 
and perforation (see Section 7.4) and making suitable 
simplifying assumptions concerning the possible in¬ 
teraction of the two adjacent materials as the projec¬ 
tile crosses an interface. 

7 2 5 Edge Effects 

If a projectile or bomb strikes near an edge of a 
concrete slab it tends to be deflected toward the edge, to 
achieve deeper penetration, and to break out concrete 
toward the edge. The effect depends not only on the 
striking obliquity and the nearness to the edge, but 
also on the design of the reinforcing used near the 
edge. 

It was concluded from .50-caliber tests at normal 
incidence that the edge effect is quite small at dis¬ 
tances greater than 6 calibers from the edge but may 
be appreciable at 4 calibers. 13 The highest striking 
velocity in these tests was about 2,000 fps and there 
was evidence that the edge effect increased, that is, 
occurred farther from the edge, with increase in strik¬ 
ing velocity. This agrees with the mechanically plaus¬ 
ible expectation that the edge effect should actually 
depend directly on the normal depth of penetration 
in calibers in relation to the distance from the edge 
in calibers. Weaker concrete permits deeper penetra¬ 
tions and, presumably, greater edge effects. Because 
of the scale effect (see Section 7.2.1), the normal cali¬ 
ber penetration for a given striking velocity increases 
with caliber; hence, for a given striking velocity the 
edge effect may be expected to increase with caliber. 
Fragmentary data from full-scale tests 30 indicate the 
possibility of the edge effect occurring as far as 15 
projectile diameters from an edge and increasing in 
normal penetration by as much as 40 per cent, com¬ 
pared to penetration in massive concrete at 8 calibers 
from an edge. These interpretations of the small 
amount of full-scale data available were purposely 
made on the safe side for the design of protective con¬ 
struction and thus probably overestimate the edge 
effect at larger scales. 

Due to the edge effect, embrasures, firing ports, 
and doors are the weakest parts of a structure. 30,31 
They are the natural points of attack and therefore 
merit particular attention in the design of fortifica¬ 
tions and other defensive structures. Further full- 
scale tests on the edge effect and means of reducing 
it are needed. 


7,2,6 Effect of Explosions 

The previous sections have dealt principally with 
the effects of inert impact on a reinforced concrete 
target. With explosive bombs and projectiles the effect 
of the explosion is superimposed on the inert effects 
preceding the instant of detonation. The effect of the 
explosion on the target is conditioned by the position 
which the missile has reached at the time of detona¬ 
tion and the deformation, if any, which the missile 
may have suffered in the process. 

The influence of sticking penetration, ricochet, per¬ 
foration, and residual velocity on the results of deto¬ 
nation have already been discussed in Sections 7.2.2 
and 7.2.3. If a missile remains intact during perfora¬ 
tion and detonates within a protective structure it will 
cause the maximum damage of which it is capable. 
This is the primary intention of the attack. Short of 
complete perforation, scabbing offers the next most 
serious possibility of damage within a heavy concrete 
structure. Figure 8 shows, at the top, front and rear 
views of a reinforced concrete slab 19 in. thick after 
the inert impact of a 75-mm projectile at 1,250 fps. 7 
The lower pictures show the same slab after the static 
detonation of a simulated high-explosive [HE] pro¬ 
jectile containing a little over 2 x /2 lb of TNT in the 
penetration hole. The incipient scab of the upper pho¬ 
tograph has been thrown off, leaving a wide rear crater 
down to the back reinforcing mat, and there is a clear 
hole through the slab. The front crater has been 
widened and the reinforcing thrown out from the 
crater. 

A useful quantity in dealing with explosive projec¬ 
tiles and bombs is the caliber charge density D c de¬ 
fined by: 

Do ~¥’ ^ 

where c is the weight of the charge in pounds and d 
is the maximum diameter or caliber in inches. From 
the definition of caliber density D (D = w/d 3 ), it 
is evident that 

De, = D ■ (2) 

w 

where c/iu is the charge-weight ratio of the missile. 
Since higher charge-weight missiles in general have 
smaller caliber densities, D c tends to be more nearly 
the same than either D or c/w for HE missiles. Its 
value seldom goes above Y± 0 lb per cu in., and many 
HE shells, SAP, and general-purpose [GP] bombs 
have caliber charge densities D c approaching this 
value. 


CONFIDENTIAL 







208 


TERMINAL BALLISTICS OF CONCRETE 




Figure 8. Front and rear view of typical crater before and after static detonation of HE projectile. 


The simulated projectile whose effects are shown in 
the lower two photographs of Figure 8 had a value of 
D c of about V 10 lb per cu in., and it was statically 
detonated at. the maximum penetration previously 
produced by an inert projectile. It is generally felt 
that these conditions will produce as severe an effect 
on a concrete target as may be gotten in combat from 
any of the usual explosive missiles for the caliber and 
striking velocity used. In this sense, Figure 8 illus¬ 
trates the maximum effect that may be expected from 
an ex|}jj#ve missile when the inert penetration before 
detonation is near the scabbing limit for the slab. 

The effect of an explosion following inert penetra¬ 


tion into a massive concrete target is illustrated in 
Figures 9 and 10. 7 The crater profiles of Figure 9 are 
based on measurements of three actual shots 7 with 
caliber charge densities of about 0.007, 0.07, and 0.11 
lb per cu in. respectively, reading from top to bottom. 
The black area in each case represents the additional 
concrete removed by the explosion following the inert 
penetration outlined by the white area. 

It is evident that the increase in penetration depth 
produced by the explosion is fairly small. According 
to a rough rule of thumb this increase in depth of hole 
is only about caliber or less for common types of 
HE missiles. 




















PHYSICAL DESCRIPTION OF PHENOMENA 


209 


It might be expected that this additional penetra¬ 
tion depth would increase with the depth of the pre¬ 
ceding inert penetration because of the increasing 
confinement of the explosive charge. In spite of at¬ 
tempts to do so, this expected tendency has not been 
found in the available observations, but it must be ad¬ 
mitted that the data show considerable fluctuations 



SLAB EFFECT OF 


EXPLOSION 



D c = 0.007 LB/IN. 3 
CHARGE/WEIGHT = 1.2 PERCENT 
FOR w/d 3 = 0.55 LB/IN. 3 



D c = 0.07 LB/IN. 3 
CHARGE/WEIGHT = 12.5 PERCENT 
FOR w/d 3 = 0.55 LB/IN 3 



D c = 0.11 LB/IN. 3 
CHARGE/WEIGHT = 20 PERCENT 
FOR w/d 3 = 0.55 LB/IN. 3 


Figure 9. Effect of penetration of inert projectiles plus 
detonation of explosive projectiles in reinforced concrete. 


from the mean. The nature of these fluctuations is 
suggested by the irregular outlines of the actual crater 
profiles in Figure 9. At least until more data on this 
point become available it may be assumed as a first 
approximation that the increase in depth, Az calibers, 
due to an explosion, is independent of the depth of 
inert massive penetration attained before the detona¬ 
tion. This even seems to give fairly good estimates 
when the missile detonates on the surface of the con¬ 
crete without penetrating appreciably before detona¬ 
tion. 

A small amount of data, such as that shown in 
Figure 8, for different caliber charge densities, has 
led to the suggestion that the increase in depth Az 
may be estimated from 

Az — 0.6(10Z) C ) 4 calibers. (3) 

Additional data are needed to test this relationship. 
This formula has been expressed in terms of the quan¬ 
tity 10 D c to facilitate making mental estimates of Az, 
since, for the most effective HE projectiles and bombs, 
10 D c will be nearly unity, as discussed above. 

The crater profiles of Figure 9 show that the lat¬ 
eral effect of the explosion is relatively larger than the 
increase in depth of the penetration hole. The increase 
of front crater was also shown on the left side of Fig¬ 
ure 8. The effect of different types of reinforcing on 
the widening of the front crater is illustrated in Fig¬ 
ure 10, where the bottom photographs, showing the 
crater after detonation, are reproduced to the same 
scale as the corresponding views before detonation at 
the top. The removal of concrete and the widening 
of the front crater are particularly important with 
repeated fire (see Section 7.2.7) or in case the weak¬ 
ened Avail or slab is subjected to subsequent attack of 
any kind. 

The effect on concrete due to the explosion of a 
bomb or other charge in contact with the slab and at 
various distances from it in air is discussed in Section 
15.2. Similarly the effect of underground explosions 
on reinforced concrete slabs and Avails is discussed in 
Section 3.7. 

In connection Avitli the design of fortifications and 
other protective structures, attention is drawn to some 
model-scale tests of contact explosions on concrete. 54 
These indicated that an advantage would be gained 
for the defender by utilizing the scab-mesh and 
spaced-slab constructions discussed in Section 7.2.4 
against contact explosions. Larger scale tests of these 
construction methods are needed. 

During World War II, a considerable amount of 

























210 


TERMINAL BALLISTICS OF CONCRETE 





Iigure 10. Front craters before and after static detonation of HE projectiles, showing effect of different types of 
reinforcing. 


development work was done on both sides toward in¬ 
creasing the effectiveness of explosive missiles against 
concrete. The Germans developed special anticoncrete 
projectiles 51,57 for artillery fire (150-mm, 210-mm, 
etc.) as well as a number of hollow charge projectiles 
and bombs which could be used against concrete as 
well as armor. 55 In England, and to a lesser extent, 
in the United States, there was interest in increasing 
the size, caliber density, and striking velocity of bombs 
for attacking concrete, especially heavy protective con¬ 
struction like the German submarine pens. A large 
amount of work was done on methods of breaching 1 
concrete antitank walls and reducing other concrete 
defenses. (See Section 7.2.7.) 


While no specially designed anticoncrete HE pro¬ 
jectiles were developed in the United States during 
World War II, a very interesting compromise solution 
was worked out to make use of standard HE projectiles 
with a special nose fuze for attacking concrete. 32 To 
obtain the maximum explosive effects that have been 
described above, two things are necessary: (1) the 
missile must remain essentially intact during the in¬ 
ert penetration stage preceding detonation, both to 
promote maximum inert penetration and to keep the 
charge and fuze in condition for high-order detona¬ 
tion, and (2) the fuze must provide sufficient delay 
to permit maximum penetration (or, in the best case 
perforation) before detonation. The latter is obviously 

















PHYSICAL DESCRIPTION OF PHENOMENA 


211 


a fuze design problem. It turns out that the former, 
also, is dependent to a great extent on the mechanical 
design of the fuze element, in the sense that the fuze 
contours, strength of parts, and method of attachment 
to standard HE projectiles (e.g., 90-mm or 105-mm) 
can be made to increase the missiles’ resistance to de¬ 
formation against concrete, and indeed, to reduce the 
probability of deformation to a practicable minimum 
under field conditions. 

For maximum effect the fuze delay should be at 
least as great as the time of penetration. On the other 
hand, it should not exceed this total time of penetra¬ 
tion by too much in case the projectile rebounds from 
the target without sticking or in case of ricochet (see 
Section 7.2.2). 

Very little work has been done on direct measure¬ 
ment of the time of penetration and not enough is 
known about the theory of penetration for computing 
this time very accurately (however, see Section 7.4). 
Until a better experimental or theoretical basis be¬ 
comes available, it is suggested that the total time of 
penetration t 1 be estimated from 15 - 16 > 18 


where a\ is the depth of maximum penetration and 
v 0 is the striking velocity. A consistent set of units is 
implied; for example, if a\ is in ft and v 0 in fps, t x 
will be in sec. This relation would be exact if the force 
resisting penetration were a constant. However, there 
are reasons for expecting that the estimate of t 1 so ob¬ 
tained will not be too far wrong in the actual case in 
which the force during penetration is not strictly con¬ 
stant. The relation given is at least simpler and even 
probably more accurate than some relations based on 
an assumed law of resisting force that have been sug¬ 
gested. 16,18,37 Equation (4) has some physical basis 
and makes allowance in the right direction for both 
x x and t' 0 . It is certainly better than assuming t x to 
be a constant regardless of caliber. 

7 - 2,7 Effect of Repeated Fire 

The effect of repeated hits on reinforced concrete 
depends on the dispersion of the points of impact and 
the degree to which the slab reinforcement tends to 
hold the debris in place to offer resistance to later 
shots. Small dispersion, for example, such that succes¬ 
sive hits fall within the spall crater of the first shot, 
is advantageous for the attack, if the object is to per¬ 
forate the slab as soon as possible with at least one 
projectile, as is often the case when a strong point is 


to be neutralized and particularly when explosive 
projectiles are available. If the object is to make a 
breach of given size as, for example, in an antitank 
wall, a relatively greater fire power is needed and the 
distribution of hits will be determined by the width 
of gap desired. 

Model-scale repeated fire tests have been made with 
.50-caliber nonexplosive projectiles. 13 Successive im¬ 
pacts were placed within a 5-in. diameter circle, that 
is, within a 5-caliber radius circle measured from the 
first impact point. Thus the later shots fell well with¬ 
in the spall-crater radius of the first shot. The strik¬ 
ing velocity was kept approximately constant, about 
1,400 fps for successive rounds. Crater profiles were 
measured at frequent intervals during the firing and 
the number of inert shots required to perforate slabs 
of various thicknesses were found. The data show that 
the additional depth of penetration due to each im¬ 
pact was in every case less than the penetration of 
the first round and that the number of rounds re¬ 
quired for perforation increased roughly as the cube 
of the thickness. This is perhaps physically plausible 
on the assumption that equal increments of energy 
delivered by successive shots remove roughly equal 
increments of concrete from the hole. However, it is 
then striking that the relation was found for perfora¬ 
tion rather than penetration and also that it holds 
(roughly) down to the single-shot perforation thick¬ 
ness. It was also concluded that multiple-layer in¬ 
ternal reinforcing increased the resistance of the slab 
to repeated fire attack, relative to that offered by 
similar slabs without internal reinforcing mats, in 
line with the previous discussion (Section 7.2.4) of 
the tendency of reinforcing to hold cracked and 
broken concrete in place. 

Some data at larger scale have been obtained on 
the effect of repeated inert fire under field condi¬ 
tions. 30 The less strictly controlled conditions make the 
analysis of these tests more difficult. It had been con¬ 
cluded, 10 however, that the depth of penetration with 
repeated fire increased at a rate somewhere between 
the second and fourth roots of the number of shots, 
and that perforation could finally result when the 
target thickness was only 2 or 3 calibers greater than 
the total depth of penetration so attained. Within the 
accuracy involved, these results tend to confirm the 
previously stated model-scale findings for larger cal¬ 
ibers. 

It should be emphasized that these results were 
found for normal, or nearly normal, incidence. The 
depth of penetration for repeated fire measured per- 




212 


TERMINAL BALLISTICS OF CONCRETE 


pendicularly to the slab face will undoubtedly de¬ 
crease with increasing obliquity, probably in about 
the ratio that the single-shot depth decreases. How¬ 
ever, for higher obliquities approaching the ricochet 
angle, or angles at which the first projectile tends to 
turn and follow a curved path in the concrete, the 
repeated fire depth may be expected to show less de¬ 
crease due to obliquity than the single-shot depth, 
because, within the craters produced by the first shots, 
the actual striking angle tends to be altered to favor 
succeeding rounds. Similar effects may be expected 
for the increased number of rounds required for per¬ 
foration as the obliquity is increased. 

Edge effects for repeated fire have been studied ex¬ 
perimentally and crater profiles determined with .50- 
caliber inert projectiles; some observations are avail¬ 
able at larger calibers in the reports already cited. In 
a general way the results follow the description given 
above and in Section 7.2.5. 

Extensive tests 50 were made in England during 
World War II on the breaching of reinforced concrete 
antitank walls by repeated fire using various specific 
combinations of inert AP shot and HE shell. The idea 
behind this pick-and-shovel tactic is that the solid 
projectiles will achieve maximum penetration, crack¬ 
ing, and breaking up of the concrete, while the less 
penetrative explosive projectiles will be more effective 
in removing rubble and cutting reinforcing from the 
section of the wall to be breached. This in turn per¬ 
mits the solid shot to reach deeper layers of the solid 
wall and the process is repeated until the required 
breach is made. 

Some of the conclusions drawn from the British 
test, listed and summarized in the reference given, 56 
are as follows. Short ranges (1,000 yd or less) are 
desirable, since random hitting is considerably reduced 
and the effect of the increased striking velocity is very 
marked. HE shells must be used in addition to the 
AP shot in the proportion of 1 HE shell to 4 or 5 
AP shot. They are necessary to cut the reinforcing 
and clear the rubble. HE shells must not be fired too 
early or too late. One or two rounds after each ten 
rounds of AP give the best results. If the firing of 
HE shells is postponed too long, all the concrete will 
have fallen away and only the reinforcement will be 
left, in which case it is difficult to hit and destroy. 
The number of HE shells should be kept to the mini¬ 
mum necessary to cut the reinforcement and clear the 
rubble. An excess of HE will reduce the rubble to fine 
dust, which does not give a good grip to tank tracks. 
Craters will also be formed, making passage of the 


gap difficult. The less the reinforcement, the more re¬ 
sistant the wall is to battering and the more shot and 
shell are required to break it up. For this situation, 
test observations run counter to the usual conclusions 
(Section 7.2.4) that reinforcement tends to hold the 
cracked and broken concrete in place. If, however, the 
reinforcement is very heavy, additional shells are 
usually required to cut it. 

This is probably the best method for breaching a 
wall with gun fire. The results obtained suggest that 
similar combination shot and shell methods would 
also be advantageous for neutralizing a concrete-pro¬ 
tected strong point whenever repeated fire must be 
used. In this case the primary object would not neces¬ 
sarily be to create a breach, but to get one or more 
explosive projectiles to detonate within the bunker 
or fortification being attacked. 

7.3 ANALYSIS OF EXPERIMENTAL WORK 

In Section 7.2 the more important terminal- 
ballistic phenomena for concrete have been described. 
A number of more or less quantitative conclusions 
have already been drawn from the experimental ob¬ 
servations discussed. 

It is the purpose of this section to show how some 
of the more important phenomena may be summarized 
and correlated by graphs, diagrams, and empirical 
formulas. The empirical formulas will, in turn, form 
the basis for the theory of concrete penetration to be 
discussed in Section 7.4. 

Throughout this section considerable emphasis is 
put on recommendations for further work, both ex¬ 
perimental and analytical. The method of Section 

7.3.3 for analyzing the normal penetration curve was 
devised toward the end of World War II. Normal 
penetrations form the point of departure for the an¬ 
alysis of scabbing, perforation, the effects of obliquity, 
etc. It is felt that the methods of Section 7.3.3 will 
form a much more accurate basis for estimating nor¬ 
mal penetrations than the various methods hereto¬ 
fore used and that the analyses of Sections 7.3.4, 7.3.5, 
7.3.6, and 7.3.7 can be much improved by using the 
new method for normal penetrations. It seems logical 
to make a number of recommendations for further 
experimental work in conjunction with the description 
of the analysis of past experiments. 

7 31 Ballistic Limits 

A graphical summary of the way in which the va¬ 
rious ballistic limits (perforation, scabbing, sticking, 


t'o\ !•'! I'KXTTAli 







ANALYSIS OF EXPERIMENTAL WORK 


213 


and ricochet) vary with striking obliquity and veloc¬ 
ity may be given in the form shown in Figures 11 
and 12. Each such diagram refers to a particular tar¬ 
get and projectile combination; the examples given 
are based on the same concrete slab and projectile as 

STRIKING OBLIQUITY 6 IN DEGREES 


10 __?- 10 



Figure 11. Thin-slab ballistic limits. Based on data of 
Figure 1. Target, 8.9 in. thick; projectile, 37-mm M80, 
weight 1.70 lb. 


the crater profiles shown in Figures 1 and 2, and in 
Data Sheet 2A3 of Chapter 19. The general form of 
the curves shown may be expected to be similar for 
any perforable concrete target and nondeforming in¬ 
ert projectile or bomb of conventional type. 

The graphs are symmetrical about the zero obliq¬ 
uity radius and only one half of the diagram would 
ordinarily be needed to present the information. The 
complete diagrams are given here to emphasize the 
fact that the perforation, scabbing, and sticking limit 
curves all cross the zero obliquity axis normally. This 
fact must be remembered when diagrams are made 
showing obliquities on only one side of 6 = 0 degree. 

These diagrams also show that the perforation, 
scabbing, and sticking limit velocities increase faster 
than secant 6 with obliquity 0. This has led to at¬ 
tempts to express the ratio of the oblique to the nor¬ 
mal limit in each case as a constant power of sec 6, 
the exponent being greater than unity. However, this 
yields only very rough agreement because the best 
exponent to fit the data for each limit appears to 
vary with both obliquity and slab thickness. 

A comparison of Figures 11 and 12 shows that the 
sticking, scabbing, and perforation limits do not al¬ 
ways occur in the same order for various slab thick¬ 
nesses. Perforation, of course, always occurs at a 
higher velocity than scabbing, since both are essen¬ 


tially back-face phenomena (see Section 7.2.3). But 
for a sufficiently thick target, sticking depends on the 
depth of penetration beyond the front face and is, 
therefore,classed as a front-face phenomenon (see Sec¬ 
tion 7.2.2). As the slab thickness is decreased, the 
scabbing-limit velocity decreases until the scabbing- 
limit curve begins to pass the sticking-limit curve, 
which is believed to change only slowly, if at all, 
down to this particular slab thickness. With a further 
decrease in slab thickness the sticking-limit velocities 
as well as the scab-limit velocities decrease, although 
the scab-limit velocities decrease more rapidly. Thus 
with the thin slab, Figure 11, sticking occurs at higher 
velocities than scabbing, but at lower velocities than 
with the thick slabs, Figure 12. If the slab is suffi¬ 
ciently thin, sticking will presumably not occur at any 
velocity, since the slab will be perforated before stick¬ 
ing can take place. 

Kicochet is also a front-face phenomenon (see Sec¬ 
tion 7.2.2), and by definition, cannot occur simul¬ 
taneously with either sticking or perforation. However, 
as shown in Figure 11, ricochet of the projectile and 
scabbing of the target can occur simultaneously. 

It is interesting to speculate on the course these 
curves should take with increasing velocity and obliq¬ 
uity: for example, on how the sticking- and ricochet- 


STRIKING OBLIQUITY 8 IN DEGREES 



Figure 12. Thick-slab ballistic limits. Based on data 
of Figure 2. Target, 22 in. thick; projectile, 37-mm 
M80, weight 1.70 lb. 


limit curves approach one another, or on the expected 
curvature of the sticking-limit curve. However, this 
is not important until significantly higher striking 
velocities are used on concrete. For the situations 
which are at present of practical interest the various 
limit curves may be expected to exhibit the general 


t' ON i iDi-;XTIAi| 























214 


TERMINAL BALLISTICS OL CONCRETE 


characteristics shown in Figures 11 and 12 and dis¬ 
cussed above. 

7 3 2 Vulnerable Areas 

The polar diagrams just described show the various 
ballistic limits as functions of striking velocity and 

STRIKING OBLIQUITY0IN DEGREES 



Figure 13. Thin-slab vulnerable areas. Based on data 
of Figure 1. Target, 8.9 in. thick; projectile, 37-mm 
M80, weight 1.70 lb, muzzle velocity 2,900 fps. 


obliquity for a specific target and a specific projectile. 
If, in addition, the muzzle velocity of the gun and the 
range-velocity relation of the projectile are known or 
assumed, it is possible to construct the vulnerable- 
area diagrams shown in Figures 13 and 14. 

A vulnerable-area diagram is, in effect, a map laid 
out with range and obliquity relative to the target 
face as polar coordinates. This map shows the outlines 
of the areas within which the gun must be placed to 
obtain sticking, scabbing, or perforation, or to avoid 
ricochet, assuming the target to be a vertical wall and 
the trajectory to be horizontal at striking. As is obvi¬ 
ous from Figure 12, the thick slab cannot be perfo¬ 
rated at all by the gun of the present example for 
which the muzzle velocity, that is, the maximum veloc¬ 
ity available, is only 2,900 fps. The vulnerable area for 
scabbing is much smaller than that for sticking. 

As the slab thickness is decreased, the scabbing area 
increases while a perforation area appears and like¬ 
wise grows. It is thought that the sticking region 
changes very slowly until the boundary of the scab¬ 
bing region overtakes it and that then, with further 
decrease in slab thickness, the sticking region ex¬ 
pands also, although not so rapidly as the scabbing 
area. For sufficiently thin slabs the phenomenon of 
sticking probably disappears entirely and the projec¬ 


tile either falls on the front or gun side of the slab 
or else perforates the slab. As shown in Figure 13, 
scabbing occurs at greater ranges than sticking for 
the thin slab while the converse is true for the thick 
slab (2V2 times as thick) of Figure 14. Comparison 
of the two figures also shows that sticking occurs at 
greater ranges (i.e. lower striking velocities) for the 
thin slab than for the thick slab. 

A vulnerable-area plot of the type shown in Figures 
13 and 14 contains practically all of the essential in¬ 
formation needed in either an operational analysis of 
the estimated effect of a single inert shot attack on a 
concrete target or in designing a concrete slab to resist 
this specific attack. Analogous diagrams for steel and 
armor plate have been used for the design of armored 
vehicles and tanks. Their use is suggested in a similar 
way in the design of fortifications. The difficulty lies 
in making quantitative predictions of the various 
vulnerable and ricochet areas for arbitrarily selected 
gun, projectile, and slab. Nevertheless, even semiquan- 
titative maps of this type will help to clarify the for¬ 
tification designer’s problem. 

If, for example, a seacoast fortification is being de¬ 
signed against 16-in. naval gunfire, only the deep¬ 
water areas from which an enemy might conceivably 
fire such weapons need be outside the area defined by 



STRIKING OBLIQUITY 6 IN DEGREES 


TARGET 


Figure 14. Thick-slab vulnerable areas. Based on 
data of Figure 2. Target, 22 in. thick; projectile, 37-mm 
M80, weight 1.70 lb, muzzle velocity 2,900 fps. 


the scabbing and ricochet limits. The designer’s prob¬ 
lem is to choose the site, orientation, and slab thick¬ 
nesses so that this will be true for each wall of the 
fortification. Since this end is to be achieved at the 
lowest cost for materials and construction, it would, 
for example, be concluded in this case that the land- 



















ANALYSIS OF EXPERIMENTAL WORK 


215 


ward walls need not be as thick as the seaward walls, 
or that even the seaward walls can be reduced in thick¬ 
ness by orienting them so that the deep-water areas 
fall within the ricochet regions for these walls. 

According to this method of analysis, vulnerable- 
area diagrams, of the type shown in Figures 13 and 
14, are made for each wall of the proposed fortifica¬ 
tion or bunker. The vulnerable-area diagram for the 
whole structure is composed of the separate diagrams 
for the walls placed in the proper relative positions to 
one another. The composite diagram is then placed 
on a map of the terrain or region chosen for the site, 
so that the vulnerable areas will actually appear as 
regions on the map. Vulnerability to other forms of 
attack can be similarly analyzed. 24 

How can a vulnerable-area diagram be made for an 
arbitrary gun, projectile, and concrete target/ One 
may assume that the range-velocity relation for the 
gun and projectile are known or can be found. The 
question then reduces to the problem of making a 
ballistic-limit diagram (of which Figures 11 and 12 
are examples) for the particular projectile and target, 
because from this a vulnerable-area diagram can be 
constructed, using in addition only the range-velocity 
relation. 

The problem of predicting ballistic limits for any 
projectile (even assuming it to be inert and nonde¬ 
forming) at any obliquity and against a given con¬ 
crete target is by no means completely solved. Present 
procedures are based on the following ideas. In the 
first place, predictions are based on experimental test 
data rather than on theory. Empirical rules found 
from penetration observations permit fairly good pre¬ 
dictions of massive penetration as a function of strik¬ 
ing velocity (at least for normal incidence) in terms 
of concrete properties, and projectile mass, caliber, 
and nose shape. Experimental data on sticking, ob¬ 
lique penetration, and ricochet are also available, but 
further work on empirical formulas describing these 
phenomena is needed. Finally, it turns out that fairly 
good linear empirical relations can be set up between 
massive penetration at a given striking velocity and 
the thickness of a slab of the same concrete that can 
be (1) scabbed and (2) perforated. Over a wide range, 
these relations seem to be independent of concrete 
properties and even hold fairly well at obliquities up 
to 40 degrees. 

If this work on concrete is compared with the corre¬ 
sponding work on steels and armor for nondeforming 
projectiles, the most striking contrast is the emphasis 


on penetration in both the experimental and theoreti¬ 
cal work on concrete, whereas the work on steel dealt 
almost exclusively with perforation. This stems from 
the fact that massive penetration is much easier to 
observe and interpret with concrete than with steel. 
Penetrations beyond the bourrelet of the projectile 
and up to 10 calibers are easily produced at ordinary 
velocities in concrete (i.e. below 3,000 fps), whereas 
with plain and armor steels it is difficult to make 
systematic massive penetration measurements even up 
to 2 calibers without projectile shatter or deformation. 
For such depths the special phenomena near the face 
of the target and those caused by the entry of the 
projectile nose into the target probably still play a 
major role, making the observations more difficult to 
interpret. 

It is felt that the theory of massive penetration 
should be less complicated than the theory of perfo¬ 
ration, because in the former only the front-face ef¬ 
fects are present, while in the latter the back-face 
effects must also be considered. Furthermore, if pene¬ 
tration is being studied, almost every shot gives a 
point on the graph; with perforation a number of 
bracketing shots are needed to determine one perfora¬ 
tion limit. It is very difficult to produce identical con¬ 
crete targets at different times and places, much more 
difficult than in the case of steels, and hence it is very 
advantageous to base the terminal-ballistic studies on 
experimental penetration curves, each of which is ob¬ 
tained from a single target, rather than to depend 
solely on the relation between perforation limits as 
determined for different targets. It is felt that the 
best method of comparing the terminal-ballistic prop¬ 
erties of concrete targets lies in comparing the respec¬ 
tive penetration curves obtained with the same pro¬ 
jectile rather than in comparing the usual engineering 
specifications and strength tests. It is felt that the 
perforation limit for a given concrete target is, for 
practical purposes, uniquely determined by its thick¬ 
ness and its massive penetration curve as obtained 
with the same projectile. 

Besides this connection with ballistic limits, the 
penetration curve is of direct practical importance in 
analyzing the effect of explosive missiles and the effect 
of repeated fire. 

7 3 3 The Dependence of Penetration on 

Striking Velocity 

A great deal of attention has been devoted to the 
problem of finding a suitable empirical formula to 
represent the observed massive penetration in con- 







216 


TERMINAL BALLISTICS OF CONCRETE 


c-rete of an inert nondeforming bomb or projectile as 
a function of striking velocity at normal incidence. 0 
This is needed not only for smoothing (since individ¬ 
ual penetrations exhibit experimental scattering from 
the mean) and for interpolation (since it is practi¬ 
cally impossible to obtain any specific striking velocity 
by adjusting the powder load) but also for extra¬ 
polation, for example, to estimate accurately the mas¬ 
sive penetration that would be obtained in the con¬ 
crete of a given slab for the striking velocity at which 
scabbing and perforation are actually observed. (See 
Section 7.3.5.) 

Lacking an adequate theory of penetration, it is 
believed that, of the empirical relations that have been 
proposed, the following is the most satisfactory both 
for simplicity and for accuracy of representation. 20 

G{z) = cV 1 - 80 , (5) 

where G(z) — z 2 /4 for 0 ^ ^ 2.00 calibers , 

= 2 —1.00 for z ^ 2.00 calibers, 

and z = nose depth at the end of penetration, in 
calibers, 

V = striking velocity in fps divided by 1,000, 
c — constant for a given target and projectile. 
This formula relates z and T r for normal nondeform¬ 
ing penetration into a massive concrete target. For 
numerical purposes it is convenient to express V in 
thousands of fps and to define the units of c accord¬ 
ingly so that G(z) will be a dimensionless quantity. 

Table 1 gives values of T 71 * 80 for T up to 3.0. The 
values given correspond to striking velocities at in¬ 
tervals of 100 up to 3,000 fps. This table will greatly 
facilitate the application of equation (5) to penetra¬ 
tion data. 


Refinements of the empirical approximation repre¬ 
sented by equation (5), particularly for values of 2 be¬ 
low 2.00 calibers, could undoubtedly be made, but the 
formula suggested has the advantages that it is simple 
in form, that it takes account of face and nose effects 
in a reasonable way, and that it involves a single 
parameter c. The latter is very important because it 
permits direct comparison of any two sets of penetra¬ 
tion data, regardless of the particular striking veloc¬ 
ities used in obtaining each. 

For the analysis of concrete penetration data (nor¬ 
mal incidence, inert and nondeforming projectile, 
massive concrete target), graph paper, as shown in 
Figure 15, based on equations (5) and (6), may be 



Figure 15. Graph on which G{z) = cF 1 - 80 represents 
straight line with slope c through origin for plotting 
normal penetration in concrete of nondeforming pro¬ 
jectile as function of striking velocity. Typical set of 
field data is plotted (37-mm 1.65-lb AP projectile, data 
on page A-35 in reference 7). Center of gravity of 
plotted points is marked -J-. For dashed line see 
Section 7.4.6. 


Table 1 . Values of F 1 * 80 for concrete penetration 
formula, equation (5).* 


V (fps) 

pi.so 

v (fps) 

P'1.80 

v (fps) 

pi. 80 

100 

0.016 

1,100 

1.187 

2,100 

3.802 

200 

0.055 

1,200 

1.388 

2,200 

4.134 

300 

0.115 

1,300 

1.604 

2,300 

4.478 

400 

0.192 

1,400 

1.832 

2,400 

4.835 

500 

0.287 

1,500 

2.075 

2,500 

5.203 

600 

0.399 

1,600 

2.330 

2,600 

5.584 

700 

0.526 

1,700 

2.599 

2,700 

5.977 

800 

0.669 

1,800 

2.881 

2,800 

6.381 

900 

0.827 

1,900 

3.175 

2,900 

6.797 

1,000 

1.000 

2,000 

3.482 

3,000 

7.225 


*v = striking velocity in fps. U= i >/1000 = striking velocity in thousands 
of fps. 


c See references 2, 3, 4, 6, 11, 15, 16, 18, 20, 22, 23, 33, 34, 
36, 40, 44, 47, 50, 52. 


used. The ordinates are laid off at distances given by 
the function G(z) and labeled with values of z, the 
abscissas are similarly laid off at distances propor¬ 
tional to F 1S0 and labeled with the corresponding 
values of v. According to equation (5), the observed 
points of any particular set of penetration data will 
be on or near a straight line through the origin; the 
slope of this straight line will be proportional to the 
parameter c. Graphical determination of this mean 
straight line offers a simple procedure for smoothing, 
interpolating, and extrapolating for any given set of 
observed penetration data. The plot not only displays 
the magnitude of the random experimental errors in¬ 
volved, but also shows just how well the empirical 
equation (5) is able to represent the mean of the ob¬ 
servations. When a sufficiently large number of such 




























































ANALYSIS OF EXPERIMENTAL WORK 


217 


plots have been made they should be reviewed to 
search for systematic deviations from the formula, 
equation (5). If found, these may in turn lead to im¬ 
provements in the formula. 

For numerical evaluations of the parameter c re¬ 
ferring to a specific projectile-target combination, it 
is suggested that the following formula is suitable 
both for simplicity and for the relative weighting of 
data : 20 


2G(*) 

y 1 yi^o 



This gives the slope of a straight line passing through 
the origin and through the center of gravity of the 
plotted data points (marked -f- in Figure 15). It also 
takes some account of the fact that absolute experi¬ 
mental errors tend to increase with distance from the 
origin, but not so fast as the coordinates themselves. 


734 The Dependence of Penetration on 
Projectile Mass, Caliber, and Nose Shape, 
and on Target Properties 

The method just outlined gives a satisfactory repre¬ 
sentation of the relation between striking velocity and 
penetration for a wide range of data regardless of tar¬ 
get properties and projectile mass, caliber, and nose 
shape, such that changes in these only affect the para¬ 
meter c in equation (5). 

Analysis of the experimental data bearing on these 
effects 20 leads to the following empirical penetration 
formula, based on equation (5) : 

G(z) = KNd^DV 1 - 80 , (8) 

where K = penetrability of the concrete, 

N = nose-shape factor for the projectile, 
d = caliber or maximum diameter of the pro¬ 
jectile (in.), 

D — w/d 3 = caliber density of the projectile 
(lb per cu in.). 

The caliber-density factor D approximates very 
well the effect of projectile mass on penetration as far 
as present data go. Additional data on the effect of 
projectile mass are greatly needed; these should be 
obtained under carefully controlled conditions, keep¬ 
ing the other factors as constant as possible while only 
the projectile mass is varied over a wide range. 

The scale-effect factor d 0 - 20 represents quantita¬ 
tively the important effect described in Section 7.2.1 
within the accuracy of present data, in which D and 


N usually have different values for the calibers to be 
compared. Additional data on the scale effect, with 
careful controls to keep K, D, and N constant for the 
different calibers, and with the larger calibers going 
well above 155 mm, will probably be required in order 
to improve this scale-effect formulation. Beyond this, 
a better understanding of the physical causes underly¬ 
ing the scale effect is needed. 

The .50-caliber data on the effect of nose shape on 
penetration are analyzed in the report cited above. 20 
This analysis results in the recommendation that the 
nose-shape factor N be estimated from 


N= 0.72 + 0.25 V»- 0.25, (9) 


when n is the radius in calibers of a tangent-ogive 
projectile nose. The dimensionless quantity n is often 
called caliber radius head [crh] in British work; it 
is denoted by r 0 in Figure 1 of Chapter 6. The radical 
in this formula is the nose height in calibers for the 
case of a tangent ogive. If the actual projectile does 
not have a tangent-ogive nose, this formula for N will 
probably still give satisfactory results provided n is 
estimated from an ideal tangent ogive which would 
most closely approximate to the actual nose shape. 

A considerable amount of small-caliber data is 
available for evaluating the effect of concrete proper¬ 
ties on the penetrability K. These data have not as 
yet been analyzed by the method of Section 7.3.3, 
and this should be done. The method of analysis used 
in reporting the .50-caliber data of the last Princeton 
Concrete Properties Survey evaluated a “penetration 
parameter” for each concrete. Examination of the 
ideas behind this earlier and less accurate method of 
analysis shows that the penetration parameter there 
used is, in general, proportional to the penetrability 
K as defined here. Hence the curves given in the re¬ 
port cited may be interpreted as showing how K varies 
with various concrete properties, although the numer¬ 
ical value of K will be different from that given for 
the old penetration parameter. More accurate values 
of K for each of the concretes should be calculated 
by the center of gravity method of equation (7), which 
with equation (8) leads to: 


K = 


Nd°- 20 V i DV 1 - S0 ’ 


( 10 ) 


The caliber density D in lb per cu in. has been put 
inside the summation in the denominator to take 
account of variations in projectile mass. Values of 
K in the interval from 2.0 to 5.0 have been found 
from typical sets of data. 20 








218 


TERMINAL BALLISTICS OF CONCRETE 


7 3 5 Analysis of Perforation and 

Scabbing Data 

As mentioned near the end of Section 7.3.2, the 
analysis of experimental observations on perforation 
has been based on the massive penetration curve ob¬ 
tained with the same concrete and projectile at lower 
striking velocities. Using the penetration observations, 
one can estimate, by extrapolation, the hypothetical 
nose penetration z t in calibers that would be obtained 
in a massive target of the same properties at the ob¬ 
served perforation limit velocity v r The actual thick¬ 
ness of the target perforated at this limit velocity is 
denoted by e and its thickness in calibers by e/d. 

Perforation tests were made with .50-caliber model- 
scale projectiles on 133 concrete slabs 12 ranging in 
thickness from 3 to 18 calibers in compressive strength 
from 1,500 to 7,000 psi, and in maximum aggregate 
size from 14 to 2 calibers. A large variety of reinforc¬ 
ing schemes was also investigated. It was found that 
within practical limits e/d is a linear function of Zi 
and that this function is the same within about 10 
per cent regardless of the target variations tested. The 
mean relationship, 

~ = 1.23 + 1.07*,, (11) 

was found for perforation. 

The scab limit velocity v s was also determined for 
each slab and the massive penetration corresponding 
to this striking velocity was estimated. As for perfora¬ 
tion, linear relations were found between the scab- 
limit thickness s/d in calibers and z 8 , the mean rela¬ 
tionship being 

4-= 2.28 + 1.132,. (12) 

d 

The values of z t and z s used in obtaining these 
linear relationships were estimated by a method which 
is probably less accurate than that described in Sec¬ 
tion 7.3.3. Using still older and probably even less 
accurate methods of estimating z t and z s , the rela¬ 
tions 10 

4 - = 1 . 32 + 1.24 2 , 

. , ( 13 > 

had previously been obtained for 37-mm, 75-mm, 
3-in., and 1.55-mm data. 7 It is not known whether the 
apparent differences between these relations and those 
determined at the .50-caliber scale are real or whether 
they are due to differences in the methods used in 


estimating z x and z 8 . The question should be resolved 
by basing the required extrapolations of the massive 
penetration data on the method described in Section 
7.3.3 and recomputing both the small- and large-scale 
data. 

At the beginning of World War II the concept of 
a proof factor was used for perforation and scabbing 
questions. It was felt that the ratio of the limit thick¬ 
ness for perforation to the massive penetration depth 
at any striking velocity would be practically constant, 
that is, about 3/2 or 4/3. The results described tend 
to eliminate the concept of proof factors and to replace 
them by the idea that the difference (instead of the 
ratio) between perforation-limit thickness and massive 
penetration at the same velocity is more nearly a 
constant in the case of concrete targets. Analogous 
statements can be made for scabbing. The constant 
difference hypothesis would hold exactly if the co¬ 
efficients of Zj and z s in the last terms of equations 
(11) and (12) were unity, in which case the perfora¬ 
tion difference or defect would be about IV 2 calibers 
and the scabbing defect about 2^2 calibers. It is pos¬ 
sible that the suggested re-evaluation of the data us¬ 
ing the methods of Section 7.3.3 would lead to some 
such formulation, but until then the perforation and 
scabbing defects mentioned can only be thought of 
as rough approximations for thin slabs. 

It should also be pointed out that the linear ap¬ 
proximations, equations (11) and (12), cannot hold 
for very thin slabs less than about 2 or 3 calibers in 
thickness. The actual relations must be curved so as 
to pass through the origin, that is, so that e/d goes 
to zero with z t and so that s/d goes to zero with z s . 
It is likely that a composite function Gj(e/d) of the 
type given in equation (6) for G(z) will be found 
to be proportional to z { and another similar composite 
function G s (s/d) will be proportional to To the 
extent that the thickness defect hypotheses discussed 
in the previous paragraph holds, the word propor¬ 
tional should be replaced by equal. 

According to this reasoning, it will be seen that 
the combination of the penetration equation (5) with 
the relations at present represented by equations (11) 
and (12) leads to equations of the form 



connecting the limit thicknesses e and s with corre¬ 
sponding limit velocities Iq and U s . The evaluation 



ANALYSIS OF EXPERIMENTAL WORK 


219 


of the functions G and the constants c and a and 
their relation to the corresponding quantities in equa¬ 
tion (5) depends on further data and analysis along 
the lines indicated above. 

1.3.6 The Dependence of Penetration, 
Ricochet, Scabbing, and Perforation 
on Obliquity 

The data analyses discussed in the last three sec¬ 
tions deal exclusively with the phenomena at normal 
incidence. Much less is known about the effect of ob¬ 
liquity on penetration, scabbing, perforation, and the 
occurrence of ricochet. In combat, however, some de¬ 
gree of obliquity is almost always present and it is 
very important not to ignore its effects. The general 
character of some of these effects was described in 
Sections 7.3.1 and 7.3.2, and illustrated, particularly, 
in Figures 11, 12, 13, and 14. 

With oblique penetration the principal quantity of 
practical interest is the component of penetration per¬ 
pendicular to the target face z p measured in calibers. 
For theoretical analyses other facts, such as slant 
depth and the curvature of the projectile path in the 
target, are also of interest and have often been re¬ 
corded in data tabulations. 

For a given projectile and target the perpendicular 
component of penetration z p is a function of two vari¬ 
ables, namely, the striking velocity and the obliquity. 
This alone makes the analysis of oblique penetration 
much more difficult than in the case of normal pene¬ 
tration which depends on only one variable, the strik¬ 
ing velocity. In addition, much less experimental work 
has been done, and the experimental scattering is 
greater for oblique fire than for normal fire, probably 
due to the fact that the turning forces, causing the 
projectile path to curve away from the direction of 
incidence, are more erratic in their effect on z p than 
the force variations which produce experimental er¬ 
rors in normal penetration. For these reasons no gen¬ 
erally applicable empirical formula has yet been found 
to express z p as a function of striking velocity and 
obliquity. 

The studies that have been made so far indicate 
that the ratio z fz, where z is the penetration at nor¬ 
mal incidence at the same velocity, is less than cos 0 
but approaches cos 0 as the striking velocity is in¬ 
creased. This is plausible on the assumptions that the 
resisting forces are roughly independent of depth and 
that the asymmetric forces deflecting the projectile 
from the direction of incidence act mainly near the 


surface of the target. As the striking velocity is in¬ 
creased, the time that these turning forces act on the 
projectile is decreased and thus its deviation from its 
original direction is decreased. 

A rough idea of the decrease in penetration of or¬ 
dinary AP projectiles caused by obliquity for striking 
velocities from 1,000 to 2,000 fps can be gained from 
the following tabulation based on a partial analysis 23 
of the data: 


0 0° 5° 10° 15° 20° 25° 30° 35° 

% 1.00 0.95 0.89 0.82 0.75 0.67 0.58 0.47 

z 

The values of zjz for any particular obliquity 0 tend 
to decrease for smaller striking velocities and to in¬ 
crease toward cos 0 as an upper bound for higher 
striking velocities. 

Even though they are probably the best available, 
there is some hesitation in giving these values because 
they seem to imply a greater accuracy than is at pres¬ 
ent justified. One reason for the large scatter of the 
experimental points probably lies in the less accurate 
methods of estimating z, the penetration at normal 
incidence for the striking velocity at which z p was ob¬ 
served. Now that the method of Section 7.3.3 is avail¬ 
able, a thorough review of all good obliquity data 
should be undertaken. 

The following points are suggested for such a re¬ 
view. At first only data obtained with AP projectiles 
of conventional shape and mass, for which penetra¬ 
tions at normal incidence on the same face of the same 
target were also recorded, should be analyzed. The 
data should be grouped by calibers. From the normal 
incidence penetrations, the 2 corresponding to the 
striking velocity for each z p should be estimated, us¬ 
ing the method of Section 7.3.3. For some calibers, 
data on concretes of widely different strengths are 
available; it is probable that the effects of obliquity 
can be better represented as functions of 2 rather than 
striking velocity. Hence, it is suggested that the analy¬ 
sis be made in terms of the function 




z cos 6 


(15) 


This function can be evaluated for each data point. 
The attempt to find an empirical formulation should 
be guided by the fact that f(z,6) = 1.000, by definition, 
and by the expectations that f(z,0) < 1.000 for 6 
> 0° and f(z,0) -> 1.000 for 2 ->- co. It may be hoped 
that f(z,6 ) will be found to be sufficiently independ¬ 
ent of the strength or penetrability of the concrete to 
permit an empirical formulation (or graphs or tables) 




220 


TERMINAL BALLISTICS OF CONCRETE 


in terms of f{z,6) for all concretes, whereas a unified 
formulation in terms of a function of striking velocity 
and 0 does not seem, a priori, so promising. 

In conducting obliquity tests it is possible to choose 

6 quite accurately while the striking velocity for each 
shot cannot be controlled so accurately. For the analy¬ 
sis of results it is a great advantage to conduct all 
obliquity tests at one or more fixed angles. Obliquities 
of 11°, 20°, 28°, and 35° have been so used in 37-mm, 
75-mm, 3-in., and 155-mm scale tests 7 to get a good 
distribution of cos 0 values; at the .50-caliber scale 
multiples of 10° were used. 12 

The effect of nose shape and projectile length will 
undoubtedly be noticeable, particularly at low veloci¬ 
ties and high angles. The analysis for such effects 
should be based on the results of the obliquity analysis 
for projectiles of conventional form and mass as out¬ 
lined above. 

Some quantitative idea of the angles and velocities 
at which ricochet begins may be gained from Figures 
11 and 12 (which refer to a 37-mm projectile of con¬ 
ventional type) and from Data Sheet 2A5 of Chapter 
19. Ricochet limits will undoubtedly be found to be 
sensitive to projectile nose shape and length, as well 
as to concrete strength. 

The relations (11) and (12) for perforation- and 
scabbing-limit thicknesses hold also for oblique im¬ 
pact up to 40° according to extensive .50-caliber 
tests, 12 provided the estimated z t and values are 
replaced by the corresponding values of z p for the ob¬ 
liquity and limit velocities in question. The graphs in 
the report cited suggest certain systematic deviations 
from the relations (11) and (12) with obliquity, but 
these are within the accuracy claimed for the relations 
up to about 40°. 

Thus the prediction of oblique scabbing and per¬ 
foration is based on the estimation of oblique penetra¬ 
tion in quite the same way as in the case of normal 
incidence. Improvements in the analysis may be 
sought by first improving the accuracy of prediction 
for oblique penetration along the lines suggested 
above, based on better evaluations of the function 
f(z,6). This in turn, should lead to a better analysis 
of oblique perforation and scabbing data. 

7 3 ' Nomograms for Estimating Penetration, 

Scabbing, and Perforation of 
Concrete Targets 

Data Sheets 2A1, 2B1, and 2C1 of Chapter 19 deal 
with penetration, scabbing, and perforation, respec¬ 
tively, of reinforced concrete by AP projectiles and 


AP and SAP bombs. These nomograms were devised 
in 1943 10 according to the best methods of data analy¬ 
sis then available. The left halves of the three dia¬ 
grams, including the striking velocity scale, are iden¬ 
tical, and are based on an empirical formula accord¬ 
ing to which the nose-corrected penetration in calibers 
is (approximately) proportional to the caliber density, 
to the three-halves power of the striking velocity, to 
a graphical scale effect function (given in Figure 18 
of the report cited), and inversely proportional to the 
square root of the compressive strength of the con¬ 
crete. The “ladder” transfer from B to C scales in 
Data Sheet 2A1 takes account of the Mi-caliber nose 
correction used in the diagram up to this point. In 
Data Sheets 2B1 and 2C1 the corresponding ladder 
scale embodies the relations (13) which were used for 
scabbing and perforation. 

No final revision of these data sheets was ever made, 
but it is felt that a considerable improvement would 
result from the material discussed in previous sections. 

7 4 THEORY OF CONCRETE PENETRATION 

The motion of a projectile is at all times governed 
by the laws of dynamics. This fact is known with 
greater precision than any of the specific observations 
and measurements which have so far been discussed 
in this chapter. The experimental conclusions and em¬ 
pirical formulas given in previous sections have, how¬ 
ever, not made use of Newton’s laws of motion. 

The aim of a theory of penetration is to go beyond 
empirical formulas and to establish a quantitative con¬ 
nection between the forces acting on the projectile 
during penetration and the observed behavior. The 
nature of these forces is not well understood for any 
target material. In many respects the theory is at least 
as well developed for concrete as it is for steel or other 
materials. 

The phenomena of projectile penetration involve 
not only very high stresses, producing strains far be¬ 
yond the elastic limit, but these occur under impact 
conditions at very high velocities. During the penetra¬ 
tion cycle the velocity decreases very rapidly to zero. 
Relatively little progress has been made toward direct 
experimental observation of the dynamic phenomena 
during the penetration cycle. 

While the ensuing discussion explicitly refers to 
concrete as the target material, the general point of 
view as well as many of the details may, with appro¬ 
priate modification, be applied to the theory for steel 
and other materials. 



THEORY OF CONCRETE PENETRATION 


221 


7A1 The Need for a Theory of Penetration 

The importance of an analytical study of such phe¬ 
nomena, as an extreme case of the strength and fail¬ 
ure of engineering materials, should not be under¬ 
rated. Some of the ways in which an adequate theory 
of penetration is of practical importance for the prob¬ 
lems of terminal ballistics are the following. 

A theory of penetration is needed to establish sound 
correlations, that is to deepen and extend the analysis 
of experimental data beyond the methods described in 
Section 7.3. In a fundamental sense, a proper attention 
to the theory of penetration is needed in planning and 
conducting all experimental work, lest the work de¬ 
volve into a series of isolated ad hoc tests aimed at 
answering specialized questions and thus obtaining 
results which can never be correlated. Sufficient data 
on actual projectile masses, diameters, and shapes, on 
striking velocities, on actual penetrations and target 
properties, etc., should always be recorded to furnish 
the basis for examining the interrelations among dif¬ 
ferent tests and for theoretical analysis. 7,11,12 

A theory of penetration is needed to give informa¬ 
tion about the resisting forces which cause projectile 
and bomb deformation; on this a more rational design 
against deformation could be based. At present there 
exists only very meager knowledge of the conditions 
of striking velocity, obliquity, and target thick¬ 
ness under which present bombs and HE projectiles 
will fail, nor is it known how to apply information 
gained by actual test with one missile to other service 
missiles. The “practical” expedient of testing all missiles 
against targets of all thicknesses is impractical. This 
is perhaps a typical example of how the lack of theory 
costs time and money in multiplying the tests needed 
and, even then, fails to provide generally applicable 
information. 

A theory of penetration is needed to provide infor¬ 
mation concerning the setback forces available for 
fuze initiation (especially with thin slabs) and the 
time thereafter to maximum penetration or to perfora¬ 
tion, in order to secure the maximum effect from the 
detonation of a given missile (see Section 7.2.6). The 
lateral and turning forces encountered in oblique im¬ 
pact need also to be better understood, both as causes 
of fuze failures and as causes of missile deformation. 

A theory of penetration is needed for predicting the 
remaining velocity of a projectile after penetrating a 
given thickness of a target material for designing com¬ 
posite targets, as discussed in the last paragraph of 
Section 7.2.4. Similarly a theory of perforation is 


needed to give information on the residual velocity 
after perforation, for example, in order to estimate the 
distance covered before detonation of a time-fuzed 
missile. 

A better understanding of the way in which the re¬ 
sisting forces vary with depth in the target, with pro¬ 
jectile shape, and with velocity is needed for the analy¬ 
sis of oblique penetration and perforation data. (See 
Section 7.3.6.) 

' 4 2 The Equation of Motion 

The fundamental problem of terminal ballistics is 
to account for the observed penetration at normal in¬ 
cidence and zero yaw of a nondeformable projectile 
into a uniform massive target. Under these idealized 
conditions the projectile penetrates in a straight line 
coincident with the direction of incidence and the rec¬ 
tilinear motion is governed by a single differential 
equation expressing Newton’s second law of motion, 
namely, 

w d 2 x _ iv vdv 

~g dt 2 = g dx = force actin S 011 projectile. (16) 

The first expression on the left is the usual product of 
mass times acceleration; the second form, which is the 
rate of increase of the kinetic energy with distance, 
is often more useful for penetration problems. The 
force acting on the projectile during penetration is, 
of course, negative when x is measured in the direc¬ 
tion of motion. 

With yaw or oblique incidence lateral forces tend to 
deflect and turn the projectile. While equation (16) 
still governs the forward component of motion of the 
center of gravity, additional equations based on the 
second law of motion must be written for the lateral 
motion and for the rotation of the projectile about a 
transverse axis. In addition, the force functions to be 
used with the several equations are, in general, de¬ 
pendent on the components of position and velocity 
involved in all of the equations. This problem is vastly 
more complicated than the fundamental simple case 
for which equation (16) was written. Attention will 
be restricted for the present to the simple problem 
specified at the outset. 

743 Scale Relations 

In order to compare the relations at various scales 
or calibers in a simple way, it is advantageous to 
eliminate w and x by introducing the caliber density 
D and the caliber penetration z, as has been done in 






222 


TERMINAL BALLISTICS OF CONCRETE 


many of the discussions of Section 7.2 and 7.3. Equa¬ 
tion (16) can then be written in the form: 


^ dv 
Du — = 
dz 


7TQ 

- ff = - 48 P ’ 


(17) 


where P is the resisting pressure in psi and g is the 
acceleration due to gravity or 32.174 ft/sec 2 . 

In the absence of a scale effect, the force function 
R will be independent of caliber. When a scale effect 
exists, as in the case of concrete (and probably to a 
lesser extent with steel), R will depend on the caliber 
d. This, however, will not affect the integrability of 
the equation of motion (16) because, for a nonde¬ 
forming projectile, d is constant during the motion 
represented by the equation. 


7 4 4 The Law of Force 

A mean value of the force resisting a projectile dur¬ 
ing penetration can easily be found by dividing the 
striking kinetic energy by the observed depth of pene¬ 
tration. For concrete targets this mean force divided 
by the cross-sectional area of the projectile may be 
from 30,000 to 100,000 psi. This calculation corre¬ 
sponds to the assumption that R is constant in equation 
(16), but if it is made for different depths of penetra¬ 
tion (same projectile and target) the mean pressure 
values are found to increase with depth, that is, pene¬ 
tration increases less rapidly than the striking kinetic 
energy. If the resisting force were constant during 
each penetration, then R would have to assume differ¬ 
ent but constant values for different striking velocities. 
This does not seem likely from a physical point of view 
and, hence, it is concluded that R is not constant, but 
varies during the penetration cycle. The crux of the 
penetration problem lies in finding out how the force 
varies during penetration, and in elucidating the phy¬ 
sical phenomena involved. 

It is common to assume that R depends on the in¬ 
stantaneous velocity, or on the depth in the target, or 
on both, that is 

R = R(z,v). (18) 

The scale effect dependence on d need not be expressly 
shown here because d does not vary during penetra¬ 
tion. 

A possible dependence of R on other variables dur¬ 
ing the motion cannot be excluded on a priori theoreti¬ 
cal grounds. The resistance arises from an interaction 
between the moving projectile and the material of the 
target which must be displaced. A pattern of motion 
or flow must be set up in the plastically disturbed or 


crushed region of the target, while elastic effects are 
propagated with finite velocity beyond the disturbed 
region. In general, the instantaneous motion of in¬ 
dividual target particles in the flow region will neither 
be exactly parallel or perpendicular (radial) to the 
motion of the projectile, although both assumptions 
have been made in simplified armor-perforation theo¬ 
ries. As the projectile advances into the disturbed re¬ 
gion the direction and rate of motion of each particle 
changes continuously and others are set into motion 
at depths beyond that reached by the nose of the pro¬ 
jectile. In this process some of the energy and mo¬ 
mentum transferred from the projectile to target ma¬ 
terial at earlier stages in the penetration cycle will 
serve to reduce both the crushing and inertial resis¬ 
tance of the target at later stages. At each stage the 
disturbed region extends laterally and well ahead of 
the actual penetration hole. 

Thus, the resistance R may well depend on the de¬ 
celeration dv/dt and on the “previous history” of the 
motion, as well as on 2 and v directly. The penetration 
cycle may involve a transient stage at the beginning, 
during which the disturbance or flow pattern in the 
target material is set up, and a subsequent quasi¬ 
steady-state stage, during which the projectile-target 
interaction depends in some continuous way on the 
relative motions of the projectile and the target mate¬ 
rial in its neighborhood. It is even possible that some 
motion of the target material continues for a brief 
time after the forward motion of the projectile has 
ceased. It is not clear how these considerations may 
be put into mathematical form and no definite sug¬ 
gestion involving other variables than those in equa¬ 
tion (18) has as yet been formulated, let alone inte¬ 
grated and compared with experiment. 

The nature of the physical phenomena causing the 
scale effect are also not understood. Among the sug¬ 
gestions that have been made are the following. (1) 
If the target is not homogeneous, but actually varies 
in penetration resistance with depth, R will depend on 
the absolute depth x rather than on the caliber depth 
2 as assumed in equation (18). (2) R may depend on 
the ratio of caliber to some characteristic length as¬ 
sociated with the granular structure of the target, for 
example, the mean aggregate size in concrete or the 
grain size in steel. (3) The flow pattern of displaced 
target material and, hence, the resisting force, may be 
a function of the projectile velocity measured in cali¬ 
bers per sec, that is, v/d. Thus a functional relation 
may exist between the resisting pressure and the rate, 
in calibers per sec, at which the plastically deformed 




THEORY OF CONCRETE PENETRATION 


223 


or crushed region advances into the previously undis¬ 
turbed target material. 

7 4 5 The Relation between Theory 

and Experiment 

The interrelation of theory and experiment in the 
concrete penetration problem is schematically shown 
in Figure 16. 16 The first three of the four boxes in 
the Experiment column have been covered in previous 


set up in Section 7.3.4. Thus, within the approxima¬ 
tions involved, the connection A in Figure 16 is estab¬ 
lished. 

7 4 6 A Theory of Penetration 

for Concrete 

The following theory of concrete penetration 20 is 
offered as a good approximation for the experimental 
data now available. It is the best that can be recom- 


THEORY 


EXPERIMENT 



Figure 16. Interrelation of theory and experiment in penetration problem. Separation between columns is almost 
complete in our present knowledge. Lines A, B, and C emphasize connections which should be examined in order to 
make progress toward more unified structure. 


sections, particularly Section 7.4. The Theory column 
begins with postulating a law of resisting force which, 
when inserted in the relation F = ma and integrated, 
leads to a rational penetration formula. This theoreti¬ 
cal formula is to be compared with experiment as in¬ 
dicated by the line marked A. The last box in each 
column indicates the direction in which fundamental 
progress should be sought, and the lines B and C show 
the cross connections which should then be examined. 

In the next section a law of resisting force, based on 
five assumptions is suggested for concrete. The equa¬ 
tion of motion can be integrated analytically and the 
resulting penetration formula agrees satisfactorily 
with the empirical formula, equation (8), which was 


mended in the present state of knowledge on the sub¬ 
ject. 

The theory of penetration for a nondeforming pro¬ 
jectile of conventional form penetrating a massive 
concrete target without yaw in a direction normal to 
the target face (zero obliquity) can be based on the 
following assumptions: 

1. The force per unit area resisting the forward 
motion of the projectile in the target can be repre¬ 
sented to a very good approximation by a separable 
force law 18 

B = cg(z)f(v), (19) 

where 2 is the depth of nose penetration measured in 









































224 


TERMINAL BALLISTICS OF CONCRETE 


calibers and v is the remaining velocity at each 
instant. 

2. The depth dependence of R can be approxi¬ 
mated by 

g(z) — - for 0 ^ z ^ 2.00 calibers, 

2 ( 20 ) 

= 1.00 for 2 ^ 2.00 calibers. 

This assumption is an attempt to take account of the 
entry of the pointed nose of the projectile into the 
target and the effect that the escape of target mate¬ 
rial during crater formation may have on R. 

3. The velocity dependence of R can be approxi¬ 
mated by 

f(v) = , (21) 

where a is a constant. Both the fractional exponent 
needed for fitting the data and the fact that f(v) 
then goes to zero with v are unsatisfactory from a 
physical point of view. These defects are associated 
with the basic lack of knowledge concerning the physi¬ 
cal causes of the velocity dependence of R, discussed 
in Section 7.4.4. 

4. The constant c is inversely proportional to 

KNd*, (22) 

where K is the penetrability of the concrete, N is the 
nose-shape factor for the projectile, d is the caliber 
and (3 a numerical exponent. The form of the assumed 
scale-effect dependence on d is again unsatisfactory, 
but until a better understanding of the underlying 
physical phenomena is attained (see end of Section 
7.4.4) it will be difficult to improve this formulation. 

5. An excellent representation of concrete penetra¬ 
tion data at all scales is obtained by assigning the 
values 

a = 1.80 and /3 = 0.20. (23) 

According to these five assumptions the law of 
force, equation (18), becomes: 

* = 2W«y*°X constant. (24) 

The numerical values of a and f3 given in equation 
(23) were found from concrete penetration data with¬ 
out assuming 2 — a = (3. The fact that they give a 
force law in which the velocity dependence and the 
scale dependence can be combined in the single factor 
(v/d) p may be significant in connection with the 
problem of the cause of the scale effect as discussed 
at the end of Section 7.4.4. 

The equation of motion (17), with the above rela¬ 
tion for R, can be integrated by separation of the 
variables 2,18 from the initial conditions at impact 


(2 = 0 and v — v 0 ) to the final conditions at the 
end of penetration (z = z x and v = 0). 

With a hybrid system of units 16 that is convenient 
for practical numerical computations, and making the 
arbitrary constant on the right side of equation (24) 
equal to (1,000) 180 /1.80, the resulting penetration 
formula is: 

G(z x ) = KNd^DV, 1 - 80 , (25) 


I 

where G(z x ) = g(z)dz, 



z, = 


K = 


N = 


z 2 /4 for 0 <; z x <; 2.00 calibers, 
z x — 1.00 for z x }> 2.00 calibers, 
final maximum nose penetration of 
the projectile in calibers (dimen¬ 
sionless), 

penetrability of the concrete (units 
are such as to make G(z x ) dimen¬ 
sionless), 

nose factor for the projectile (di¬ 
mensionless), 

caliber or maximum diameter of 
the projectile (in.), 
weight of projectile/^ 3 , 

“caliber density” of the projectile 
in lb per cu in., 

t? o /1.000 = striking velocity of the 
projectile in thousands of fps. 

By dropping the subscripts on 2 and V, equation (25) 
becomes identical with the empirical formula, equa¬ 
tion (8), obtained from analyzing normal penetration 
data (without using the equation of motion) in Sec¬ 
tion 7.3.4. Thus the connection marked A in Figure 
16 is established. 

In the units given above, the resisting force per 
unit maximum cross-sectional area of the projectile 
is, from equations (17), (24), and (25) 

263,820 /V 
KN l d 


d 


D = 


V n = 


0.20 


P = 


g{0 P si ; 


(26) 


where V is the instantaneous remaining velocity of 
the projectile in thousands of fps, and d is in in. 

Integrating the equation of motion to find the re¬ 
lation between v and 2 during penetration gives 


G(z) /v\ 1,80 . 
G(z x ) \v 0 ) 


(27) 


It can be shown 18 that the values of v and 2 which 
satisfy this equation for given values of v 0 and z x 
will lie on a straight line having intercepts ( 0 , 2 ) and 
(^ 0 , 0 ) in Figure 15 of Section 7.3.3. For the sample 
set of data plotted in Figure 15 the maximum nose 






ADDENDA 


225 


penetration z x is 11.1 calibers when the striking veloc¬ 
ity v 0 is 3,000 fps. The dashed line shows the relation 
between z and v during this penetration according to 
equation (27). Thus the remaining velocity when the 
nose of the projectile has reached a depth of z = 8.0 
calibers is, approximately, v = 1,560 fps. This method 
of estimating the remaining velocity may be used in 
the analysis of composite slabs discussed at the end of 
Section 7.2.4. 

The time a in msec from the instant of impact to 
any depth z during penetration may be computed 
from 18 



= dimensionless function of 2 and z x , (28) 


where x is the nose penetration in feet ( x — zd/ 12). 
The total time of penetration, a x msec, can be deter¬ 
mined from 18 


K = 


2 1 



dz 


[ 


1 


G(z) “l 171 - 80 

G( z i) J 


= dimensionless function of z x only, 



where x x is the maximum nose penetration in ft 
(x x = z x d/ 12). The right sides of these equations are 
universal functions for concrete, independent of the 
target and projectile parameters K, N, d, and D. 
Thus, by numerical evaluation of the integrals, a 
graph can be made for finding values of V 0 (t/x, and 
V 0 * x /x x . Then the determination of a or a x is re¬ 
duced to a simple slide-rule operation. This method 
of estimating penetration times may be used to solve 
problems regarding fuze settings for attacking con¬ 
crete. 


7.5 ADDENDA 

751 The Solenoid Method for Measuring 
Phenomena during Penetration 

As indicated in the last box on the right side of 
Figure 16, the most promising way of improving the 
present understanding of penetration would be to 
obtain direct experimental observations of phenomena 
during penetration. Until these are obtained, theo¬ 
retical considerations, such as those given in Section 
7.4.4, will continue to be tentative and speculative. 
Even measurements of the total time of penetration 
alone would be most helpful. 


The experimental work 17 deals with an experimen¬ 
tal method of measuring velocity as a function of 
time during penetration in nonmagnetic and noncon¬ 
ducting media like concrete. The basic ideas involved 
in this method are as follows: 

The electromotive force induced by a longitudinally 
magnetized projectile (considered as a point dipole 
with a magnetic moment of M electromagnetic units) 
moving with a velocity v cm per sec along the axis 
of an idealized circular coil of N turns and r cm 
radius, is 

e = lcvf(x) volts, (30) 


where h = 
and f(x) = 


6ttMN 

iov 


volt-sec/cm, 


x _ 

( 1 —j— .T 2 ) 5/2 

dimensionless position function, 


(31) 


(32) 


where x is the instantaneous position of the dipole on 
the coil axis measured in coil radii from the center 
of the coil. The position function f(x ) is plotted in 
Figure 17. In the absence of a resistant target, v is 
sensibly constant and x is proportional to the time i 
measured from the instant t — 0 when the dipole is 
at the center of the coil. For this case Figure 17 is a 



Figure 17. Position function fix) for single coil. 


picture of the form of the emf pulse as a function of 
time as commonly obtained from each coil in the sole¬ 
noid method of measuring projectile velocities. If 
the projectile strikes a resistant target (nonmagnetic 
and nonconducting) placed near the coil, the emf 
pulse will be changed because v changes and because 
x is no longer proportional to t. On the assumption 
that the magnetic moment M does not materially 
change after impact it is possible to deduce the pro¬ 
jectile velocity as a function of time from an accu- 
































226 


TERMINAL BALLISTICS OF CONCRETE 


rately recorded oscillographic trace of the emf pulse 
as a function of time. 

A more direct determination of velocity as a func¬ 
tion of time can be obtained by using two identical 
coaxial coils connected in opposition and spaced a 
distance of 0.90 diameter apart. Measuring x (in coil 
radii) from the point on the common axis midway 
between the coils, the induced electromotive force 
becomes 

e = kvF(x) volts (33) 

where F(x) = f(x + 0.90) —f(x — 0.90). (34) 

This two-coil position function is shown in Figure 18, 
together with the two single-coil components of which 



Figure 18. Position function F(x) for two opposing 
coils, 0.90 diameter apart. 


it is composed. The flat-top region of the graph illus¬ 
trates the fact that F(x) — 0.4085 and is constant 
within ± y 3 per cent, while the dipole is in the interval, 

— 0.3 < a; < 0.3, (35) 

between the coils. Hence, in this interval, equation 
(33) becomes 

e = OAOSokv volt, (36) 

that is, the induced electromotive force is proportional 
to the projectile velocity at each instant and is inde¬ 
pendent of x to a very good approximation. The oscil¬ 
lograph trace will give directly the velocity as a func¬ 
tion of time while the magnetic center of the projec¬ 
tile is in the interval (35) ; the target should there¬ 
fore be placed so that the decelerations to be observed 
occur in this interval. 

It is of some scientific interest to point out that this 
two-coil arrangement is very closely related to a two- 
coil arrangement specified by J. C. Maxwell 58 for 


obtaining a nearly uniform magnetic field gradient 
near the axjs midpoint. Maxwell’s spacing between 
coils is \/3/2 = 0.866 diameter; the 0.90-diameter 
spacing is a compromise which serves to extend the 
useful interval (36) somewhat without materially 
affecting the constancy of F{x) for practical purposes. 
I he underlying connection between the present ar¬ 
rangement and Maxwell’s becomes clear if the dipole 
is considered as moving in the magnetic field of a 
current flowing in the coils and the rate of work done 
on the dipole is equated with the additional power 
required by the current to overcome the induced 
electromotive force. 

The two-coil arrangement not only has the advan¬ 
tage over the single-coil system of greatly simplifying 
the routine analysis of the recorded oscillograph 
traces, but it makes it easier to assess the accuracy of 
the resulting v(t) curves and to recognize imperfec¬ 
tions in the recording system which might otherwise 
lead to erroneous v(t) curves. 

Experimental work using the two-coil system is 
reported in reference 17, particularly the aspects of the 
initiating and recording system and the problem of 
stabilizing the bullets to reduce the change in magnetic 
moment during impact to a minimum. Satisfactory 
performance was obtained with .50-caliber Service AP 
bullets, and the problem of stabilizing model-scale 
artillery type bullets had just been begun when the 
work was interrupted in order to transfer the available 
personnel to a more important problem. 

‘ 5 2 Summary of x4nalytical Theories of 
Penetration and Perforation 

The theory of concrete penetration presented in 
Section 7.4 is one among many that have been con¬ 
sidered analytically. The following summary of the 
various mathematical possibilities is presented to aid 
those who will carry forward the theory of penetration 
and perforation, either for concrete or for other 
materials. 

Summary of Integrable Force Laws 

The various integrable forms of R(z,v) that have 
been proposed may be summarized under two general 
classes of analytical force laws 18 

Separable: Ii = a ■ g(z) ■ f(v ), (37) 

Generalized Poncelet: E = a- g(z)i'P -j - b-y(z)v 2 . 

(38) 

Since a nondeforming projectile is considered, d will 
remain constant during the motion. Hence any scale 


























ADDENDA 


227 


effect dependence of R on d need not appear explicitly 
in these hypothetical force laws in order to permit the 
formal integration of the equation of motion, equa¬ 
tion (17). Delations for penetration and perforation 
obtained by integrating this equation are collected 
in Table 2. Figure 19 shows some of the theories 
which fall under these two general classes of force 
laws, as special cases. Thus, the classical theories 2 of 
Robins-Euler, Poncelet, and Retry maybe considered as 
special cases of either equation (37) or equation (38). 

The constants a and b have been written as factors 
separate from the functions of z and v in these equa¬ 
tions. In this way g(z), y(z), and f( v) can be thought 
of as dimensionless functions which may remain the 
same for a given type of target (such as steel or con¬ 
crete) while the constant parameters a and b absorb 
the necessary physical dimensions and have different 
values for different targets of the same type. Both 
the relations between v and 2 during penetration and 
the relations for residual velocity after perforation 
have been put in a form not involving a , b } and D in 
Table 2 in the expectation that this form would be 
invariant for all targets of one type. 



Figure 19. Classification of penetration theories. There 
are shown some of the theories obtained by successive 
specialization (indicated by arrows) of the two general 
analytical force laws of Table 2. 


Table 2. Summary of analytical theories of penetration and perforation. 



Separable force laws 

Generalized Poncelet force laws 


Dv ~ = — a-g(z)-f{v) 
dz 

Dv^- = —|^a-< 7 (z)v 0 + &-y(z)-v 2 J 

Penetration 

Penetration formula 

(Relation between Vo and zi) 

D-F(y o) = a-G(zi) 

D-v o 2-0 = (2-/3) a-G(zi) 

Relation between v and s 
during penetration 

F(v) G{z) 

F(v o) *" G(z ,) 


Perforation 

Limit velocity 

D-F{vi) = aG e 

Dv?-e= (2 —0)aG e 

Residual velocity 

F (tv) = F(v o) — F(vi) 

V r 2 ~P‘M e ( Z e ) = Vo 2 ~& — Vi 2 ~& 

Where 


r % 


. f v vdv 

») = / 7T-: 

J o /W 

M{z) = € 


f Z 

[ z 

G{z) = / M(z)-g(z)dz • 


G(z) = J g(z)dz 

J o 


f Z e 

Ge - / g e {z)dz = constant 

J 0 

{2-P) b [ Z 

D ~ / yeG)dz 

Me(z) = e 0 



Ge = j 6 Me(z)-g e (z)dz = constant 



€ = base of natural logarithms 
















































































228 


TERMINAL BALLISTICS OF CONCRETE 


If the function g(z) has some form such as is sug¬ 
gested in Figure 20, it can take account of target 
face and projectile nose effects, at least qualitatively. 
(Compare item 2 in Section 7.4.6.) For small values 
of 2 , the resistance R must be smaller than after the 



Figure 20. Hypothetical form of depth dependence 
function g(z) in equation (37) or (38). 


full projectile nose has entered the target and after 
target material can no longer escape from the original 
target volume as petals or spall. In the deeper layers 
of the target the displaced material is more confined 
and g(z) may level off to a fairly constant maximum 
value (which may be made unity by defining the para¬ 
meter a properly). As soon as the material at the 
back face of the target begins to yield or rupture, R 
must begin to decrease, perhaps very rapidly or even 
abruptly as is suggested by the dashed curve for g e (z) 
in Figure 20. In the region of massive penetration, 
g e (z) and g(z) should conincide, the position of the 
dashed portion of g e {z) being determined by the dis¬ 
tance from the back face of the target. The depth z e 
at which g e (z) becomes zero will be near e/d, but it 
may be greater than e/d with a ductile material like 
steel or it may be less than e/d with a brittle material 
like concrete. 


The first term on the right in equation (38) repre¬ 
sents the crushing resistance of the target, while the 
second term represents the inertial resistance of the 
displaced target material in the sense of the classical 
Poncelet theory. 23 The problem of the form that y( 2 ) 
should have is more elusive than that for g(z). It 
may be plausible to give y (z) and y e (z) forms similar 
to those suggested for g(z) and g e (z) in Figure 20, 
and for similar reasons; certainly y e (z) should also 
become zero for some value of z near e/d. 


Time of Penetration 


In addition to the relations shown in Table 2, the 
time-depth relation during penetration can be cal¬ 
culated from one or both of the two expressions 



(39) 

(40) 


provided either that v can be expressed as a function 
of 2 in equation (39) or that R from equation (17) 
can be expressed as a function of v in equation (40). 
The latter is especially useful for sectional pressure 
theories, for which R = af(v), as shown in Figure 19. 
Particular interest attaches to the total time to max¬ 
imum penetration z x which is important in estimating 
fuzing times. It has been suggested 15,16,18 that the 
dimensionless combination 


v 0 t x v 0 t x 

K = — = 13-^4 

x x z x d 


1 d(z/z x ) 
v/v 0 


(41) 


is a useful parameter for such problems since its 
value will be near 2.0, as may be seen by regarding 
K as the ratio of the striking velocity v 0 to the aver¬ 
age velocity during penetration x x /t x . The dimension¬ 
less quantity K used in equation (29) of Section 
7.4.6 is the same as K in equation (41), although 
different units w r ere used for velocity and time. 












Chapter 8 


TERMINAL BALLISTICS OF PLASTIC PROTECTION 


si INTRODUCTION 

lastic protection is the American name for a 
material originally developed by the British and 
called by them plastic armor. a ^> c This material has 
been further developed both abroad and in this coun¬ 
try, and has proved useful as a protective material 
requiring relatively small amounts of strategically im¬ 
portant materials. Its chief use is for protection 
against small-caliber bullets or fragments. 

811 Description of the Material 

Plastic protection consists of a layer of stones em¬ 
bedded in a mastic of asphalt and filler, backed by a 
thin plate of mild steel and having a layer of expanded 
metal embedded in the mixture near the front face. 
The approximate proportions by weight for the main 
component are: 60 per cent stone, 30 per cent lime¬ 
stone dust filler, 10 per cent asphalt or other bitu¬ 
minous binder. These materials are thoroughly mixed 
at a temperature high enough for the asphalt to be¬ 
come molten and to wet the filler and stone, and the 
mixture is then poured into molds or onto backing 
plates. The stone-bitumen mixture can be poured from 
the mixing oven directly against the wall of a struc¬ 
ture; this is sometimes done to protect certain parts 
of a ship from strafing attack by planes. In its most 
common form plastic protection is furnished in slabs 
that can be bolted to the walls of structures or fitted 
together to form walls around objects to be protected. 

8 2 BALLISTIC BEHAVIOR OF 

PLASTIC PROTECTION 

Plastic protection is a mixture of hard stones and 
soft bituminous filler. Because of this heterogeneous 
nature, it must be expected that projectiles of a par¬ 
ticular variety striking various points on the surface 
of the material will penetrate in different ways and 
that the depth of penetration will vary over a wide 
range. Projectiles will be deflected by the stones, will 

a Pertinent to War Department Projects CE-5 and CE-6 
and to Navy Department Projects NO-11, NO-12, and 
NS-145. 

b For definition of ballistic terms, see Chapter 5. 

c See Weapon Data Sheet 2C2 of Chapter 19. 


yaw, and may be broken if they suffer glancing impact 
against a stone at a high velocity. Thus the process of 
penetrating into a slab of given thickness at a given 
striking velocity can occur in a large number of ways, 
some of which may result in perforation of the slab 
by the projectile or parts of a broken projectile, 
others not. Consequently, there is no sharply defined 
limiting velocity for perforation. One can only specify 
that, for a given thickness of plastic protection, bul¬ 
lets striking with low velocity will generally be 
stopped, only a small fraction perforating. As the 
striking velocity is increased, the fraction perforating 
the slab will increase, and at very high striking veloc¬ 
ities a large fraction of the bullets striking the target 
will perforate. If, on a graph, a plot is made of the 
proportion of the striking bullets that perforate, as a 
function of striking velocity, the result will be similar 
to each of the curves of Figure 1. 

821 Statistical Interpretation of 

Perforation Data 

The large variety of ways in which a bullet can 
penetrate plastic protection, some of them leading to 
perforation and others not, can be treated statistical¬ 
ly. 1 If all details of the mechanism were known, all 
methods of penetrating could be determined and the 
fraction of these leading to perforation could be 
found for each striking velocity and for each slab. 
This information is not known, and the results must 
be found experimentally by firing a large number of 
bullets and counting the perforations to determine the 
percentage through. This must be done for a number 
of striking velocities to determine one of the curves 
shown in Figure 1, and must be repeated at several 
striking velocities for slabs of different thickness, or 
weight per unit area, to determine a full set of curves. 
Each point on one of these curves is an average value 
of the percentage through, and to be reliable each 
point must be based on a large number of rounds fired. 
Standard statistical methods may be used to determine 
the reliability of each point and thus to determine 
the reliability of each curve or series of curves. 

The determination of the ballistic properties of 
plastic protection by the statistical treatment referred 
to above requires firing a large number of rounds if 





229 



230 


TERMINAL BALLISTICS OF PLASTIC PROTECTION 



STRIKING VELOCITY IN FPS 


Figure 1 . Per cent through as function of striking velocity for various weights of plastic protection, attacked by .30- 
caliber AP M2 bullets at normal incidence. Curves for /4-in. mild steel and h£-in. armor plate are included for comparison. 
(Shape of mild steel curve is estimated.) 


the result is to be reasonably reliable. This has been 
done for only one type of plastic protection and using 
only one bullet, the .30-caliber armor-piercing [AP] 
M2. The results are shown in Figure 1. Curves for 
mild steel and for armor plate are included in the 
figure for comparison. The steepness of the curves 
for mild steel and for armor show why perforation- 
limit velocities for these materials can be determined 
simply by bracketing; the difference between the ve¬ 
locity for complete protection and the velocity for 
certain perforation is small. The phenomenon is en¬ 
tirely different from that of perforation of plastic 
protection and statistical methods are not usually 
necessary. 

The curves show that at low striking velocities 
plastic protection is not so good as an equal weight 
of mild steel or armor plate, since the steel and armor 
stop all bullets, while a few get through the plastic 
protection. At higher velocities the plastic protection 
is better than either the mild steel or armor, since it 
stops some of the bullets while the other materials are 
perforated by all bullets that strike with high enough 
velocity. As a specific example, the curves show that 
plastic protection having a weight of 30 lb per sq ft 
is inferior to mild steel of the same unit weight for 
.30-caliber AP M2 bullets striking normally with 


velocities below 2,120 fps, but is superior to the mild 
steel at higher velocities. At a striking velocity of 
2,250 fps all the bullets will perforate the mild steel 
while only 40 per cent of them (on the average) will 
perforate the plastic protection. 

Statistical Methods 

Different statistical treatments of the data have 
been suggested. 1 The most promising method is based 
on the hypothesis that the percentage through may be 
represented as a normal probability integral function 
of the thickness, or weight per unit area, for a given 
striking velocity, but present data offer no proof that 
this method is better than others. Mathematical details 
of the statistical methods of analysis and interpreta¬ 
tion of the perforation data for plastic protection are 
also given. 

8 2 2 Behavior at Obliquities 

The comparison between plastic protection and mild 
steel or armor, shown in Figure 1, is for bullets strik¬ 
ing at normal incidence. At obliquities other than 
normal, the comparison is even more favorable to 
plastic protection at high velocities and just as good 
or slightly better at low velocities. 

Ricochet 

Fewer ricochets are observed from plastic protec- 


























































SPECIFICATIONS OF COMPONENTS 


231 


tion than from mild steel or armor when both are 
subjected to oblique attack under the same conditions. 
For .30-caliber AP M2 bullets striking with a velocity 
of about 2,800 fps, ricochets have not been observed 
for obliquities of 45° from the normal and it is neces¬ 
sary to increase the obliquity to 60° from the normal 
before a majority of the bullets begin to ricochet. The 
other bullets are embedded in the slab. This behavior 
is much better than that of mild steel or armor plate 
for uses in which prevention of ricochet is desirable. 

8 2 3 Protection against Explosions 

No extensive tests of the protective value of plastic 
protection subjected to explosions have been made. 
Slabs of British Mark II plastic armor, 1% in. thick, 
with a 20-gauge mild steel face plate and %6-iu- 
mild steel backing plate have been tested by contact 
explosion of hand grenades and mortar bombs. 2 A 
British-type 36M hand grenade was detonated in 
contact with such plastic protection; no perforations 
were observed, and the backing plate was only slightly 
bent. Similar results were obtained by detonating 
grenades 15 in. from the panels, and by detonating a 
grenade in contact with panels and over a joint be¬ 
tween panels. A British 2-in. Mark I mortar bomb 
was fired to strike panels of plastic protection with a 
velocity of 210 fps. The bomb detonated instantane¬ 
ously, and although the front of the panel was dam¬ 
aged, only slight bending of the backing plate was 
observed. There were no perforations. 

8 .2.4 Protection against Shaped Charges 

The use of plastic protection for protection against 
shaped charges is discussed in Chapter 14. 

83 SPECIFICATIONS OF COMPONENTS 

Extensive tests of plastic protection have been made 
only with the .30-caliber AP M2 bullet. Such tests 
have been made of plastic protection of several dif¬ 
ferent compositions, and limited tests have been made 
using large missiles. 

The best specification of components, based on these 
tests, is as follows. 

1. The stone size should be at least three times 
the diameter of the missile to be stopped. Flints and 
quartzites are the most effective of the easily available 
stones. 

2. The stone content should be approximately 60 
per cent by weight, the mastic approximately 40 
per cent. 


3. The mild steel backing plate should be between 
10 and 30 per cent of the weight of the panel. 

4. The thickness of panel should be 9 to 10 times 
the diameter of the missile to be stopped. 

831 Effect of Variation of Components 

The effect of varying the thickness, or weight per 
unit area, of plastic protection is shown in Figure 1. 
The effects of varying some of the other specifications 
have been studied by testing panels with small-caliber 
bullets, and the results of these tests are outlined be¬ 
low. These results are tentative, since the large num¬ 
ber of tests needed to establish statistically significant 
differences have not been made. 

Type of Stone 

Test panels have been made using a wide variety of 
types of stone. The results of testing these panels show 
rather conclusively that flint and quartzite are better 
than other easily available materials, and that softer 
or weaker stones are not satisfactory. 

Similar tests have been made of panels containing 
steel balls in a plastic binder. 3 No direct comparisons 
between this and the normal variety of plastic protec¬ 
tion have been made. 

Size of Stone 

Panels made of stone of several sizes have been 
tested, and panels using stone of uniform size and 
stone of graded sizes have been tested. The results of 
these tests show that the average dimensions of the 
stone should be at least three times the diameter of 
the attacking bullet, and that the use of stone of a 
more or less uniform size results in slightly better 
protection than is provided by an equal quantity of 
stone graded in size up to a maximum of about three 
times the bullet diameter. 

Type of Mastic Bindepc 

Several mastic binders have been used, and a choice 
between asphalt and coal-tar pitch cannot be made on 
the basis of present knowledge. A few panels were 
made for experimental purposes using gelatin binder 
and these were definitely inferior to those made with 
asphalt or coal-tar pitch binders. Tests of slabs made 
with different types of asphalt indicate that the binder 
should have a high tensile strength, but this conclu¬ 
sion is based on a small amount of data and the tests 
do not include materials of a very high tensile 
strength. It is quite possible that after a certain ten¬ 
sile strength is reached, a further increase in tensile 





232 


TERMINAL BALLISTICS OF PLASTIC PROTECTION 


strength of the binder will add very little to the pro¬ 
tective value. 

Proportions of Materials 

Slabs have been made using various proportions of 
stone and mastic binder. It has been found that the 
best protection for a given weight of material per 
square foot is given by a mixture containing between 
55 and 65 per cent of stone by weight. If the stone 
component is more than 70 per cent by weight there 
may be difficulty in pouring the mixture into vertical 
molds. Most plastic protection used at present con¬ 
tains about 60 per cent of stone by weight. 

Backing Plate 

Slabs made with and without backing plates have 
shown by test that a backing plate adds materially to 
the protection. Without a backing plate, material may 
be ejected from the back face, while a backing plate 
tends to keep the material in place and thus aids the 
material in stopping the bullet. 

A number of tests have been made in attempts to 
find a substitute for steel to be used for the backing 
plate. The only satisfactory materials are other 
metals; these are usually more expensive but may be 
used if a nonmagnetic material is needed. They have 
no advantage over steel in terms of protection. Armor 
plate is slightly better than mild steel for use as a 
backing plate, but the extra protection can be attained 
more economically by using mild steel and a thicker 
slab of plastic protection. Plywood, fiber board, and 
similar materials are definitely inferior to steel. 

In the present designs of plastic armor, the backing 
plate is usually from 10 to 30 per cent of the weight 
of the slab. The optimum thickness has not been de¬ 
termined. 


Front Plate or Expanded Metal Reinforcing 

Slabs have been made with and without a front 
plate of mild steel or armor. If the slabs are of equal 
weight per square foot (those without the front plate 
being thicker) the protective value is not significantly 
different for bullets striking normally. For bullets 
striking with obliquity, more ricochets occur from 
slabs having a front plate. 

Expanded metal or some similar material is usually 
placed in the slab of plastic protection as an aid in 
holding the material together under heavy attack and 
to act as reinforcing for additional structural strength. 
It has been found that the addition of a layer of ex¬ 
panded metal is advantageous and that it is somewhat 
better to place the material near the front of the slab 
than to place it in the center. 

84 RECOMMENDATIONS FOR 

FUTURE WORK 

Plastic protection is a new material and has not 
been investigated thoroughly. It is a promising mate¬ 
rial for protection against small-arms fire and against 
fragments, and does not use large quantities of stra¬ 
tegically important materials. For these reasons fur¬ 
ther investigations of plastic protection are highly 
desirable. 

The usual means of determining the ballistic merit 
of a material in terms of thickness required to stop 
missiles having given characteristics and striking 
velocity cannot be used in studying the behavior of 
plastic protection. Statistical methods of analysis and 
interpretation must be used, and these methods re¬ 
quire a large number of tests if the results are to be 
significant. 



Chapter 9 


TERMINAL BALLISTICS OF SOIL 


9i INTRODUCTION 

S oil has been used more in military protective con¬ 
struction than any other material, from the para¬ 
pet and parados of a foxhole to the large embankments 
used in major fortifications and the earth cover above 
deep underground storage of materiel. The use of very 
large bombs capable of deep penetration into soil re¬ 
quires a knowledge of the factors controlling the pene¬ 
tration of a missile into soil. The advent of the atomic 
bomb gives increased importance to a knowledge of 
these factors, since one obvious countermeasure to it 
is construction deep under ground. New weapons must 
be designed that are capable of penetrating to great 
depths so that buried enemy targets may be neutral¬ 
ized by deep explosion. Furthermore, it is essential to 
know what depth of burial will make our own vital 
points relatively safe against the weapons expected 

from the enemy. a Uc 

9 L1 Studies of Soil Penetration 

Most of the work on penetration into soils prior to 
World War II consisted of the determination of param¬ 
eters in empirical equations that had been developed 
for other materials, with no systematic attempt to find 
whether the assumptions implied in the form of these 
equations were valid in the case of soils. 

The early work on penetration into soils done in 
World War II consisted chiefly of ad hoc tests of spe¬ 
cific projectiles or bombs, usually over a very limited 
range of velocities, and compilations of the depths of 
penetration of bombs dropped onto various soils. In 
many instances the dimensions and weight of the mis¬ 
sile, the striking velocity, or the characteristics of the 
soil were not included in the reported data so that the 
results of these special tests cannot be correlated with 
each other or reduced to general relations. In 1943 the 
Committee on Passive Protection Against Bombing 
[CPPAB], National Research Council, in preparing 
a report on terminal ballistics and explosive effects, 10 
found that the information available on penetration 

a Pertinent to War Department Projects CE-5 and CE-6 
and to U. S. Navy Project NO-12. 

b See Chapter 5 for general discussion of terminal ballistics. 
c See Weapon Data Sheets 2A2*, 2A2a, and 2Cla in 
Chapter 19. 


of bombs and projectiles into soil was entirely inade¬ 
quate. Consequently, at the request of the Office of 
the Chief of Engineers, U. S. Army, the commit¬ 
tee (later called the Committee on Fortification De¬ 
sign [CFD]) initiated a study of the terminal ballistics 
of soils. This was carried out by the committee in co¬ 
operation with Division 2, NDRC, and employed the 
Ballistics Laboratory of the Princeton University Sta¬ 
tion of Division 2. The results were reported to the 
Chief of Engineers, U. S. Army. 1 This test consisted 
of a systematic, though limited, study of the effects of 
striking velocity, projectile shape and weight, and soil 
type and condition on the penetration of projectiles 
and bombs into soils and into composite targets of 
earth and other materials. The Road Research Labo¬ 
ratory [RRL] of the Department of Scientific and 
Industrial Research (British) has also recognized the 
inadequacy of earlier information on penetration into 
soils and has made a systematic study of the effects of 
several variables on projectile penetration into soils, 
chalk, and gravel. 2,3 

9 2 PHYSICAL PHENOMENA THAT 
ACCOMPANY PROJECTILE 
PENETRATION 

The penetration of projectiles and bombs into soils 
is characterized by wide variations in penetration ob¬ 
served under apparently identical conditions. These 
variations are attributed to instability and tumbling 
of the projectile and to the curved trajectory usually 
observed near the end of the penetration path. The 
penetration is dependent on many of the physical 
properties of the soil, such as the grain size and dis¬ 
tribution, the density and degree of compaction, the 
moisture content, and the presence of large stones or 
voids. For example, a projectile will penetrate from 
two to three times as far into rich clay as into coarse 
sand; thus stratification of the soil or other variations 
in composition along the trajectory will have an ap¬ 
preciable effect on the depth of penetration. 

Projectiles penetrating a cohesive soil generally 
form conical craters, wide at the entrance and taper¬ 
ing for nearly the full length of the penetration path. 
A large mass of soil is displaced by the projectile, the 


233 



TERMINAL BALLISTICS OF SOIL 


234 


soil in front of the projectile being compacted and 
sometimes pulverized. Near the surface, projectiles 
meet a comparatively small resistance to motion, since 
the surface breaks away and relieves the compaction. 
Farther below the surface the soil has been compacted 
by the overburden so that the resistance to deforma¬ 
tion and to penetration increases with depth. If a pro¬ 
jectile strikes soil at high obliquity it will tend to 
curve-toward the surface, attempting to stay in a re¬ 
gion of small resistance to motion. If the obliquity is 
great enough, the projectile will ricochet (see Weapon 
Data Sheet 2A5 of Chapter 19). 

Ordinary projectiles are unstable in end-on motion 
through earth and tend to assume a side-on attitude. 
Once a projectile starts turning sideways, the forces 
resisting forward motion are asymmetrical with respect 
to the projectile and the trajectory will be curved. The 
projectile may even come to rest with the nose point¬ 
ing back toward the point of entry. Blunt-nosed pro¬ 
jectiles are more stable in motion in soils, with the 
possible exception of sands and gravel, than sharp¬ 
nosed projectiles; since they topple less quickly they 
present a smaller area to the soil and therefore have 
less resistance to motion. 

Projectiles striking coarse sand at high velocity 
crush the sand into a fine powder. Jacketed Service 
bullets striking coarse sand at velocities above about 
1,800 fps have the jacket stripped from the core and 
at higher velocities the jacket is torn into small pieces. 
At lower velocities the jacket is not stripped but is 
deeply scored. 


9-3 EXPERIMENTAL INVESTIGATIONS 
OF PENETRATION INTO SOIL 

Experimental investigations of penetration into soils 
require a knowledge of the shape and weight of the 
projectile used, its striking velocity and obliquity, the 
characteristics of the soil, and the effects achieved. 
The striking velocity of the projectile may be meas¬ 
ured with any of the standard chronographs that have 
been developed for this purpose. Physical characteris¬ 
tics of the soil should be determined, including the 
classification of the soil, the grain size and distribu¬ 
tion, the moisture content, the bulk density, and the 
dry density. Physical properties of the soils, such as 
the shearing strength, the compressibility, the bearing 
strength, and the Proctor needle penetration pressure, 
have not yet been related to penetration resistance, but 


if an analysis of the results is to be attempted in terms 
of the physical properties of the target, measurement 
of these and other properties should be made by the 
standard methods used in soil mechanics. 

The effects on the target normally include the depth 
of penetration, the diameter of the conical crater at 
several depths, information on toppling of the projec¬ 
tile and curvature of the path, and any other data that 
may be desirable for special purposes. The objective 
of experimental work on penetration of projectiles 
and bombs into soils is to relate the measured effects 
on the target to the characteristics of the projectile, 
the striking angle and velocity, and the properties of 
the target. 

931 Experimental Work at Princeton 

In the fall of 1943 CFD of the National Research 
Council initiated a series of tests on terminal ballistics 
of soils using the range facilities of the Princeton 
University Station, Division 2, NDRC. The results of 
these tests were reported in July 1944 to the Chief of 
Engineers, TJ. S. Army. 1 

O y J 

Penetration Tests 

Penetration tests were made by firing .50-caliber 
special projectiles into a box filled with soil or into a 
mound of soil with a smooth face; all firings were 
horizontal and normal to the target surface. Velocities 
from 500 to 3,000 fps were obtained by using different 
powder charges, and the velocity of each round was 
measured by an Aberdeen-type chronograph using 
metal foil screens. Solid steel projectiles having vari¬ 
ous nose shape/ 1 .50-caliber jacketed Service ammuni¬ 
tion, and U 2 -in. steel spheres were used. Ogival-nosed 
projectiles of 1.5-caliber radius and having three dif¬ 
ferent masses were fired to determine the effect of 
mass on penetration. 

Sand, loam, and a rich clay were used as target ma¬ 
terials. The characteristics of these soils as used are 
given in Table 1. The sand and the loam were placed 
in a large wooden box, 4 ft square and 2 ft deep, hav¬ 
ing a cloth face supported by wide-mesli wire screen¬ 
ing on the aiming side. The rich plastic clay was stiff 
enough to hold its shape and was built into a mound 
about 5 ft wide, 8 ft long, and 2 ft high with a smooth 
vertical face on one side. 

Two or three projectiles were fired into each target, 
using well-separated aiming points. Each projectile 

d Flat, hemispherical, ogival of 1.5-caliber radius, and 
ogival of 3.1-caliber radius. 







EXPERIMENTAL INVESTIGATIONS OF PENETRATION INTO SOIL 


235 


Table 1. Physical characteristics of soils used in 
ballistic tests at Princeton. 


Type of measurement 

Target material 
Sand Loam Clay 

Mechanical analysis (% by weight) 




Coarse sand, larger than 0.25 mm 

90 

36 

14 

Fine sand, 0.05 to 0.25 mm 

10 

26 

9 

Silt, 0.005 to 0.05 mm 

0 

99 

19 

Clay, smaller than 0.005 mm 

0 

16 

58 

Plastic limit, moisture (% by weight) 


21 

32 

Liquid limit, moisture (% by weight) 

• • . 

27 

60 

Plastic index 


6 

28 

Properties of the soils as used for 
penetration tests 




Moisture (% of dry weight) 

3 

18 

35 

Dry weight (lb per cu ft) 

100 

108 

84 

Proctor needle pressure (psi) 

150 

290 

40 


was then recovered by digging along the trajectory by 
hand, and the position of the projectile and the length 
of trajectory measured. A projectile can be recovered 
easily in clay because the crater remains open after 
penetration. The craters in sand collapsed and careful 
digging was necessary to find the projectiles without 
changing their positions. 

The target was rebuilt and recompacted for each 
group of shots. Measurements of the density, compac¬ 
tion, and moisture content were made at frequent in¬ 
tervals. 

Penetration Tests in Sancl. All six types of projec¬ 
tiles were fired into sand at velocities of 500 to 3,000 
fps. All of the projectiles were unstable and toppled 
at striking velocities above 800 fps. The trajectories 
were curved and the projectiles were frequently found 
to have undergone lateral motion from the point of 
impact as great as one-half the penetration. In some 
cases the path of the projectile through the sand could 
be determined by traces of discoloration, crushed or 
dried sand, or warm places in the sand, but in most 
instances the only measurements that could be made 
were the final position of the projectile with respect to 
the entrance point and its orientation. 

There was a wide scatter in the data for penetration 
of each of the projectiles into sand. Penetration 
depths and lateral offsets differing by more than 30 
per cent were common for rounds fired under sup¬ 
posedly identical conditions. 

No appreciable difference in the penetration of pro¬ 
jectiles having the same mass but different nose shape 
was found. Projectiles having the same size and shape 
but different masses penetrated to different depths in 
sand, the lighter projectiles, of course, penetrating 


less. Projectiles having ogival noses of 1.5-caliber ra¬ 
dius, equal lengths, and masses differing by 30 per 
cent had penetrations differing by 11 per cent at same 
velocity. The 1 / 2 -in. spheres had a mass 27 per cent of 
the mass of the projectiles with hemispherical noses 
and at the same velocity penetrated about 65 per cent 
as deep as those projectiles. 

The .50-caliber ball M2 Service projectiles showed 
severe scoring of the copper jacket when fired into 
sand at low velocities. At velocities above about 1,600 
to 1,800 fps the jackets were stripped from the cores, 
and at higher velocities the jackets were torn to small 
pieces. 

Tests were made by firing into sand targets having 
different compactions and different water contents. 
These are related by the fact that the dry unit weight 
(weight per unit volume of dry component) due to a 
given compaction depends upon the moisture content 
of the soil. Changing the dry unit weight either by 
compaction or by changing the moisture content had 
approximately the same effect on penetration. Targets 
of low dry unit weight allowed greater penetration of 
the projectiles than highly compacted targets; increas¬ 
ing the dry unit weight from 91 to 103 lb per cu ft 
resulted in a decrease of about 20 per cent in penetra¬ 
tion depth. 

Penetration Tests in Loam. The penetration tests 
in loam soil were similar to those in sand. The same 
projectiles were fired over the same range of velocities, 
and penetration depths and lateral offsets were meas¬ 
ured for each round. No tests were made of loam 
targets having different compactions or moisture 
contents. 

The results were similar to those found in the tests 
of sand targets. The projectiles were unstable and 
toppled in the soil, the long-nosed projectiles becom¬ 
ing unstable at slightly lower velocities than the flat- 
and hemispherical-nosed projectiles. The scatter in the 
data for rounds fired under apparently similar condi¬ 
tions was not so great as in sand. 

The blunt-nosed projectiles penetrated farther in 
the loam soil than did the sharp-nosed projectiles of 
the same mass. Compared to the projectile having an 
ogival nose of 1.5-caliber radius, the flat-nosed projec¬ 
tiles showed an increase in penetration of 15 to 20 per 
cent, the hemispherical-nosed projectiles showed an 
increase of about 7 per cent, and the projectiles having 
ogival noses of 3.1-caliber radius showed a decrease in 
penetration of less than 5 per cent. The blunt-nosed 
projectiles were stable in motion at higher striking ve¬ 
locities than were the sharp-nosed projectiles, and the 























236 


TERMINAL BALLISTICS OF SOIL 


lateral offsets of the blunt-nosed projectiles were 

/ 

smaller. 

Very few of the projectiles of different mass were 
fired into the loam target. The results were similar to 
those found in sand, but the small quantity of data do 
not allow definite conclusions. 

The .50-caliber ball M2 Service bullets were fired 
into loam soil at velocities varying from 1,000 to 
2,700 fps. Only a few rounds were fired, but the re¬ 
sults were similar to the results in sand, with the 
jackets stripping from the cores at velocities above 
about 2,200 fps. 

Penetration Tests in Clay. Penetration tests in rich 
plastic clay were made by firing the various types of 
projectiles into a mound of clay having a smooth ver¬ 
tical face on the aiming side. The craters remained 
open after the penetration and it was possible to trace 
the complete trajectory of each round. The blunt- 
nosed projectiles were usually stable in motion in clay, 
traveling for almost the entire length of the trajectory 
before toppling. The sharp-nosed projectiles toppled 
and moved sidewise through the clay. 

The difference in penetration depth for the projec¬ 
tiles having different nose shapes was very pronounced 
in clay. Compared with the projectile having an ogival 
nose of 1.5-caliber radius, the flat-nosed projectiles of 
the same mass penetrated 60 per cent farther, the 
hemispherical-nosed projectiles penetrated about 15 
per cent farther, and the ogival projectiles having an 
ogive radius of 3.1 calibers showed a decrease of about 
5 per cent in penetration. 

Projectiles having different mass but the same nose 
shape showed different penetrations, the light projec¬ 
tiles penetrating to smaller depths when fired at the 
same velocity. Only a few very heavy projectiles were 
fired, and the light projectiles having ogival nose 
shape of 1.5-caliber radius were unstable and showed 
wide variations in penetration, so that no exact con¬ 
clusions can be drawn from the data for projectiles of 
this shape and of different masses. The ^-in. spheres 
had a mass 27 per cent of the mass of the projectiles 
with hemispherical noses and penetrated about 68 per 
cent as far as these projectiles. 

A number of .50-caliber ball M2 Service bullets were 
fired into the plastic clay. None of the jackets was 
stripped. 

No tests were made using clay targets of different 
compaction. An attempt was made to test the penetra¬ 
tion resistance of dried powdered clay but this was not 
successful. 


Perforation Tests 

Tests were made using parapets built of soil, with 
sloping front and back faces. These parapets were 
tested by repeated fire, using .50-caliber ball M2 Serv¬ 
ice bullets, and the number of rounds required to per¬ 
forate parapets of various sizes was determined. No 
chronograph was used, the velocities being determined 
from a calibration of the gun in terms of the powder 
charge. It was found that parapets with sides sloping 
one vertically on one and one-half horizontally were 
not good protection except for impact more than 12 
in. (24 calibers) below the top of the soil; projectiles 
striking nearer the top curved upward and came out 
of the top of the parapet. 

A cover of tarpaulin or similar material, stretched 
tightly over the top of the parapet and anchored to the 
base, increases the resistance to perforation by re¬ 
peated-fire attack. The increase in protection varies 
with different soils and is greater for dry soils than 
for wet soils. 

Perforation of Sand in Bags. Sand bags were simu¬ 
lated by building a box with two cloth sides and filling 
it with sand. The box was tapered, being thicker at 
one end than at the other, so that different thicknesses 
of sand could be tested. It was found that the cloth 
held the sand in place and thus caused an increase in 
resistance to motion of the projectile and of the mass 
of sand around the projectile. Rounds fired at veloci¬ 
ties just below the perforation limit velocity caused a 
very tight packing of the sand against the rear cloth 
face. Rounds fired at slightly greater velocities per¬ 
forated the target and ripped a hole several inches in 
diameter in the back cloth face; sand was ejected from 
the back of the target with sufficient velocity to cause 
a sandblasting effect on lumber 4 or 5 ft away. 

The thickness of sand between two cloth faces 
needed for protection is the same or slightly less than 
the depth of penetration of the projectile into the 
same sand with no confinement. Tightly packed sand 
gives much more protection than the same thickness 
of loose sand, and moist sand is slightly better than 
dry material. 

Composite Targets. A number of tests were made 
by firing vertically downward onto concrete slabs cov¬ 
ered with loam soil. Concrete slabs IV 2 , 3, and 4Vfc in. 
thick were used and various thicknesses of soil were 
placed on top of the different slabs. The .50-caliber 
solid steel projectiles were used in all tests, and the 
striking velocity of each round was measured. The re¬ 
sults have been reported to the Chief of Engineers, 
U. S. Army. 4 

%j 




RESULTS OF TESTS 


237 


93 2 Penetration by Bombs 

Many measurements of depths of penetration of 
bombs into soils have been made. These data have usu¬ 
ally been obtained by probing into the crater and 
there is no way of knowing whether the probe was 
stopped by the nose, tail, or tail fins of the bomb, or 
by a large rock. Bombs usually take a J-shaped tra¬ 
jectory under ground, curving forward in the direction 
of the line of flight of the aircraft. If the curvature is 
great a probe will not follow the path to the base of 
the bomb and the trajectory- and penetration-path 
length cannot be measured without excavation. British 
measurements of bomb trajectories in chalk have been 
reported and show typical underground paths. 5 

Published compilations of bomb penetration data 
should be consulted for additional information. 6,7 In 
using these compilations, care must be used in com¬ 
paring the results of measurements made by different 
methods and in comparing penetrations into soils that 
are not completely described. 

933 Penetration by Large-Caliber 

Projectiles 

There is very little reliable data on the penetration 
of large-caliber projectiles into soils. The experimental 
methods are difficult because the underground trajec¬ 
tories of large artillery projectiles are so long that 
considerable excavation is necessary. If small projec¬ 
tiles are used to minimize the difficulties of excavation 
the projectiles may be moved or lost with consequent 
loss of data. Furthermore, it is not known whether or 
not there exists a scale effect that may impair the re¬ 
liability of predictions based on small-scale tests. 

Some data on penetration of large projectiles have 
been recorded. 6,8 Most of the information on penetra¬ 
tion by large-caliber projectiles into soils is based on 
the extrapolation of small-scale experiments conduct¬ 
ed as described in Section 9.3.1. The available data 
on penetration by large projectiles and bombs must be 
used to confirm the methods of extrapolation. 

9,3 4 Penetration by Rocket Projectiles 

Rocket projectiles perform in the same way as other 
projectiles in penetration, with the possible exception 
of different stability due to the long body. Many pres¬ 
ent rockets are simply modifications of ordinary pro¬ 
jectiles with rocket motors attached. 

Experimental work on penetration of rocket projec¬ 
tiles into soil is described in Volume 1 of the Sum¬ 
mary Technical Report of Division 3, NDRC. These 


experiments show that control of underground motion 
can be achieved by properly shaping the nose of the 
rocket. 

94 RESULTS OF TESTS 

No complete theoretical treatment of penetration 
into soils has been developed. The experimental work 
using projectiles having the same nose shape and dif¬ 
ferent masses, described in Section 9.3.1, shows that 
the penetration of these projectiles at a given velocity 
is not proportional to the mass of the projectile. Thus 
soil penetration does not follow a relation based on a 
sectional-pressure theory (see Chapter 7). If penetra¬ 
tion is not directly proportional to the mass of the 
projectile, the obvious conclusion is that the resistance 
to motion is not dependent on the velocity alone but 
must also depend on depth. This might be expected 
for soils, since the compaction increases along the 
path. 

Empirical relations between the striking velocity, 
projectile mass, projectile nose shape, type of soil, and 
length of penetration path have been devised and are 
presented graphically in Data Sheets 2A2* and 2A2a 
of Chapter 19. 

941 Dependence of Penetration on 

Striking Velocity 

The dependence of the length of the penetration 
path in soil on the striking velocity of the missile is 
given graphically in Data Sheet 2A2*. No analytical 
expression for these empirical curves has been found. 
The dependence of the penetration path length on the 
velocity is different for each soil and for each projec¬ 
tile shape in the same soil, and the differences cannot 
be treated by simple multiplicative factors. 

94 2 Dependence of Penetration on 

Projectile Mass 

The small-caliber penetration data described in Sec¬ 
tion 9.3.1 show that the penetration-path length is not 
directly proportional to the projectile mass. An analy¬ 
sis of the penetration data for projectiles having the 
same shape and different masses shows that the pene¬ 
tration is proportional to a power of the mass between 
0.25 and 0.40. The value Vs gives a good fit to the 
data and one then obtains: 

£ = W-f(v), 
x (w\* , 

or (1) 
where x is the penetration-path length in in., d is the- 




238 


TERMINAL BALLISTICS OF SOIL 


projectile diameter (or caliber) in in., W is the pro¬ 
jectile weight in lb, and f(v) is the function express¬ 
ing the dependence of penetration on velocity. 

The small amount of data for penetration of large- 
caliber projectiles into soils and the available data for 
penetration of bombs into soils have also been studied 
and have been found to be in agreement with equation 
(1). The value of the exponent of the weight has not 
been determined with great accuracy, largely due to 
the scatter in the available data. The value Vs fits the 
data well enough to allow penetration predictions hav¬ 
ing an accuracy of ±20 per cent. 

Equation (1) is considered reliable for projectiles 
having caliber densities W/d 3 between 0.15 and 0.65 
lb per cu in. This equation must be used with the 
curves given on Data Sheet 2A2* of Chapter 19 which 
give f(v) as a function of the striking velocity v. For 
soils having compositions differing from those listed 
on the data sheet, and for projectiles of other nose 
shapes, one must interpolate between the curves. 

9 4 3 Dependence of Penetration on 
Projectile Nose Shape 

The curves given in Data Sheet 2A2* of Chapter 
19 show the different dependence of penetration on 
striking velocity for projectiles of three nose shapes. 
The penetration is always greater for blunt-nosed pro¬ 
jectiles since these show less tendency to topple and 
therefore usually have straighter underground trajec¬ 
tories than do sharp-nosed projectiles. 

9 44 Shape of Underground Trajectory 

Most projectiles and bombs have curved under¬ 
ground trajectories, so that the final depth of pene¬ 
tration is less than the length of the penetration path. 
For striking obliquities of 30 degrees or less, measured 
from the normal to the surface, the underground tra¬ 
jectory of bombs is such that the final depth below the 
surface is 70 to 90 per cent of the penetration-path 
length. For striking obliquities greater than 65 or 70 
degrees from the normal to the surface, the missile is 
likely to have a very short underground trajectory 
and to ricochet. For intermediate obliquities the pene¬ 
tration is usually shallow with a large forward offset. 

Very little is known about the magnitude of the 
offset of bombs in underground travel except that this 
offset, the tail of the J-shaped trajectory, is generally 
in the direction of flight of the aircraft dropping the 
bomb. A graphical representation of a number of ob¬ 
served offsets is given in a British study of bomb pene¬ 
tration. 5 


Bombs and projectiles striking hard or resistant 
layers of soil are usually deflected. If a bomb strikes 
a horizontal layer of rock or other resistant material 
near the end of its normal underground trajectory, it 
will tend to travel along the hard surface. 

9 4 5 Perforation of Soil Parapets 

Soil parapets used for protection should be built 
with sides having a slope no greater than 1 on P /2 to 
insure against slipping when struck by projectiles. 
For protection against single hits, the thickness along 
the line of fire should be at least three times the ex¬ 
pected penetration-path length in a large mass of the 
same soil, and to resist repeated fire of 10 hits close 
together the thickness along the line of fire should be 
about five times the expected penetration-path length 
of a single hit. The addition of a tarpaulin stretched 
tightly over the surface of the parapet and anchored 
to the base will increase the protective value. For .50- 
caliber bullets adequate protection is not provided 
except for levels 12 in. or more below the top of the 
soil because the bullets curve upward and come out of 
the top with appreciable residual velocity. No infor¬ 
mation is available on the distance below the top for 
protection against larger projectiles. 

946 Perforation of Sand in Bags 

Sand in bags is a good material for stopping small- 
caliber bullets. The sand should be very tightly packed 
in the bags, and the protection is better if the material 
is moist. Sand parapets should be built so that the 
thickness is at least as great as the expected pentra- 
tion of the attacking weapon into a large mass of the 
same sand with no confinement. 

9 4 7 Perforation of Composite Targets of 

Concrete and Soil 

Composite targets of concrete and soil should al¬ 
ways be constructed with the soil on the attacker’s 
side. If the concrete has Q per cent of the thickness 
needed for protection with no soil cover, then soil 
having a thickness of 100 — Q per cent of the pene¬ 
tration-path length to be expected in a large mass of 
the same soil should be used to provide adequate pro¬ 
tection. If the protection is against bombs or projec¬ 
tiles having striking velocities below 1,000 fps, the 
thickness of the soil should be about 25 per cent 
greater. If the protection is against high-velocity 
weapons the soil thickness may be slightly less. 

If the thickness of soil cover over concrete is great 
enough to retain the projectile, there is always the 



THEORIES OF PENETRATION INTO SOILS 


239 


possibility of a tamped side -011 explosion of a delay- 
fuzed projectile that fails to perforate the concrete. 
(See Chapter 3 for discussion of explosions in earth.) 

9 48 Model Tests of Soil Penetration 

Much valuable information on penetration into soils 
can be obtained by model testing. Equation (1) and 
the curves of Data Sheet 2A2* of Chapter 19 indicate 
that for model tests of penetration into soils the model 
projectiles must be geometrically similar to the pro¬ 
totype and of the same density. Comparison of data 
for bombs and for small-caliber projectiles indicates 
that if the soil particles are small compared with the 
projectile, scaling of the soil is not necessary. No in¬ 
vestigation has been made of the effect of overburden 
on a soil on penetration. This may be important in 
small-scale studies of deep penetrations. 

95 THEORIES OF PENETRATION 

INTO SOILS 

A number of theories have been suggested to repre¬ 
sent the performance of projectiles penetrating re¬ 
sisting mediums. The more important of these theo¬ 
ries are reported in the bibliography. 9 (See also 
Chapter 7 of the present volume.) 

951 Sectional-Pressure Theories 

Most of the theories suggested for penetration into 
soil are based on the assumption that the pressure, or 
force per unit area, resisting the projectile motion is 
dependent on the velocity of the missile and not de¬ 
pendent on the depth of penetration. This assumption 
leads to the conclusion that if the target characteris¬ 
tics, striking velocity, and projectile shape are held 
constant the final depth of penetration is directly pro¬ 
portional to the sectional pressure (weight divided by 
cross-sectional area) of the projectile. Such theories 
are called sectional-pressure theories and predict that 
for projectiles of the same diameter and striking ve¬ 
locity but of different masses the penetrations into a 
given target should be directly proportional to the 
masses of the projectiles. As shown in Section 9.4.2, 
this is not in agreement with the experimental facts. 
This indicates that penetration into soil does not fol¬ 
low a sectional-pressure theory and that the force re¬ 
sisting the motion varies with depth. 

Penetration into soil can still be described by a 
sectional-pressure theory if the dependence of the re¬ 
sisting force on depth be attributed entirely to the 


increase in cross-sectional area presented to the soil 
by toppling of the projectile, the resisting force being 
the product of the force per unit area which is de¬ 
pendent only on the velocity and the cross-sectional 
area of the projectile as presented to the soil, which 
increases as the projectile topples. According to this 
hypothesis the penetration of spheres into soils should 
follow a simple sectional-pressure theory (since 
spheres cannot topple). No data on penetration of 
spheres of different densities are available, and no 
test of this hypothesis has been made. 

95 2 Sectional-Energy Theories 

If the pressure resisting the motion of a projectile 
through soil depends on the depth of penetration and 
not on the velocity of the missile, the final depth of 
penetration must be some function of the striking 
kinetic energy of the projectile divided by its cross- 
sectional area. Theories based on this assumption are 
called sectional-energy theories. One conclusion from 
such theories is that for projectiles having the same 
shape and diameter the final depth of penetration into 
a given target must be proportional to the striking 
kinetic energy of the projectiles. Comparison of the 
penetrations of projectiles having different masses 
and fired at velocities such that the striking kinetic 
energy will be the same, shows that penetration into 
soils does not follow a sectional-energy theory. It ap¬ 
pears, therefore, that the force resisting the motion 
does not depend on the depth alone. 

9 5 3 Requirements of Penetration Theory 

for Soils 

A satisfactory theory of penetration into soils must 
cover the instability and consequent toppling of pro¬ 
jectiles. The resisting pressure, or force per unit area, 
may depend upon the velocity, the depth, or both. In 
any case, the total force resisting the motion is the 
product of this pressure and the cross-sectional area 
presented to the soil by the projectile, and so must 
increase as the projectile topples. 

In Section 9.5.1 it was shown that the pressure, or 
force per unit area, resisting the projectile motion is 
not dependent on the velocity of the projectile alone, 
and in Section 9.5.2 it was shown that this pressure 
is not dependent on depth alone. One may expect any 
satisfactory theory of penetration into soils to include 
a force that depends upon both the depth of penetra¬ 
tion and the velocity of the missile at all points along 
the trajectory. 




240 


TERMINAL BALLISTICS OF SOIL 


9 6 RECOMMENDATIONS FOR 

FUTURE WORK 

Since burial in earth is one of the most obvious 
protections against aerial attack and was being used 
on an increasingly large scale at the end of World War 
II, it can be expected to be one of the primary de¬ 
fensive devices of the future. The introduction of the 
atomic bomb will undoubtedly accelerate this trend. 
While present knowledge of the terminal ballistics of 
earth is not by any means complete it is probably ade¬ 
quate in most respects for present needs, or, at any 
rate, is consistent with the state of knowledge in com¬ 
parable fields. But since the development of weapons 
and of defense against weapons will not maintain the 
status quo it is necessary to examine present knowl¬ 
edge in the light of future needs. 

The following possibilities seem important: 

1. First-priority targets, such as command and 
communications centers, shelters for very important 
personnel, etc., may be at very great depths, possibly 
hundreds of feet; other important targets, including 
power stations, vital manufacturing plants, stores of 
weapons, or other equipment, will also be buried. The 
two questions that will arise are: Can the enemy’s pro¬ 
tection be defeated by any means? Have we adequate 
protection against the enemy’s weapons? 

2. High-explosive (as contrasted to atomic) weap¬ 
ons will continue in use. No doubt these may be larger 
and contain a more powerful explosive than present 
weapons and may be delivered to the target by other 
means, but their mode of action will be no different. 
Such weapons may be capable of very great striking 
velocities and penetrations greatly exceeding those 
now possible. 

3. Atomic weapons may be designed for creating 
earth shock. To do this they will have to be able to 
penetrate to very great depths to achieve maximum 
efficiency. The mechanism within the bomb must be 
able to withstand the resulting deceleration without 
either failure or premature action. 

4. The fuzes used with high-explosive weapons of 
the future will be capable of finer adjustment than 
present fuzes in order to cause detonation at the most 
desirable point of an underground trajectory. With 
deep penetrations this will be an important con¬ 
sideration. 

5. Bombing accuracies will be far better than are 
now possible. On this account, and because individual 
weapons will be very much more expensive and com¬ 
plex than are present bombs, it will be economical to 


have weapons that are equipped with adjustments for 
securing optimum performance against specific tar¬ 
gets. In order to take full advantage of the potential¬ 
ities of future weapons it must be possible to predict 
their trajectory and behavior before exploding. 

On account of the probabilities that have been men¬ 
tioned, the following investigations ought to be made: 

1. Penetrations into mediums other than those al¬ 
ready studied, such as gravel and soft rock, ought to 
be investigated. It is probable that soft earth is an 
extreme case, in that penetration in it is governed by 
its density while steel and concrete are equally ex¬ 
treme in the other direction in that penetration is gov¬ 
erned by strength. For intermediate materials, such 
as soft rock, both strength and density may be of com¬ 
parable importance. Of course, the striking veloc¬ 
ities must cover a range extending far above those 
now used. 

2. The time-distance relation during penetration 
will be needed for accurate fuzing of weapons. This 
requires either a better knowledge of the mechanics 
of penetration than we now have or a large number 
of direct measurements of the time-distance relation 
during actual penetrations. Such measurements might 
be a necessary preliminary to the development of a 
penetration theory. Again, a wide range of striking 
velocities, including high velocities, must be used. 

3. A knowledge of the forces and decelerations of 
projectiles in earth and soft rock is needed. A pene¬ 
trating weapon must have a case strong enough to 
withstand the greatest forces acting on it. On the other 
hand, excessive strength is generally undesirable since 
it reduces the amount of explosive. Furthermore, the 
fuzes and other mechanisms designed to operate just 
prior to detonation must be able to withstand the 
greatest decelerations to which they are subjected. 

4. The stability of a projectile in earth is of great 
importance. Present projectiles tend to turn sidewise 
during penetration. This effect is generally undesir¬ 
able since it reduces the total penetration consider¬ 
ably. On the other hand, instability may sometimes be 
desirable for limiting penetrations. Presumably, in¬ 
stability depends on the density of the medium and on 
the weight and dimensions of the projectile, especially 
its nose shape. It is known from small-scale experi¬ 
ments that blunt-nosed weapons are the more stable. 
Stable underwater rockets have been developed and 
many are found to be stable in earth. A systematic 
study of this problem is recommended with the aim 
of designing weapons of maximum stability. 


i m\ J'li'KN I'l U. i 





RECOMMENDATIONS FOR FUTURE WORK 


241 


5. The existence of a scale effect should be tested, 
since small-scale experiments are far more economical 
than large. 

6. The influence of gravity, i.e., of the earth pres¬ 
sures due to gravity forces, needs study if very great 
penetrations are under consideration. Under normal 
penetrations, gravity pressures are so small in compar¬ 
ison to the dynamic forces opposing the motion of a 


projectile in earth that only the latter are important. 
On the other hand, if penetrations are of the order 
of hundreds of feet, the influence of the static earth 
pressure may be considerable. 

7. The resistance of targets composed of earth in 
combination with other materials, especially concrete, 
needs study at large scales to supplement and confirm 
the results of the small-scale tests that have been made. 









Chapter 10 


THE FRANGIBLE BULLET FOR USE IN AERIAL GUNNERY TRAINING 


101 INTRODUCTION 

T he investigations presented here are the results 1 
of an attempt to solve the problem of training 
aerial gunners by having them fire live ammunition 
at an attacking pursuit airplane, thus simulating the 
conditions of combat. It was hoped that a bullet could 
be found that would be able to withstand the stresses 
in the firing process but be defeated by relatively 
light armor and therefore be suitable for use in a 
training program. 3 

The project had its initiation in the late spring of 
1942 and was carried out on an unofficial basis by 
Division 2 at Princeton and Duke Universities. In 
March 1944, the project was brought under official 
NDRC auspices and was carried on under a contract 
(OEMsr-1284) at Duke University and under sub¬ 
contracts with the Bakelite Corporation and the 
American Time Products Company. 

Many other groups contributed significantly to the 
technical and organizational aspects of the project. 
These included the Frangible Bullet Project, Laredo 
Army Air Field, Laredo, Texas; the Remington Arms 
Company, Bridgeport, Connecticut; the Explosives 
Department, E. I. DuPont de Nemours Company, 
Wilmington, Delaware; the Air Technical Service 
Command, A.A.F., Wright Field, Dayton, Ohio; the 
Ballistics Research Laboratory [BRL], Aberdeen 
Proving Ground; Frankford Arsenal and the Phila¬ 
delphia Suboffice of the Ordnance Department; Opera¬ 
tions, Commitments, and Requirements, A.A.F. Head¬ 
quarters, and Air Ordnance A.A.F., Washington, 
D. C.; the Schnacke Manufacturing Company, Evans¬ 
ville, Indiana; Eglin Field and Buckingham Field, 
Florida, and the Fort Worth Headquarters, Training 
Command, A.A.F. 

io.2 FUNDAMENTAL INVESTIGATIONS 

10 - 2 - 1 The Plastic Bullet 

As a result of preliminary tests carried out at Duke 
and Princeton Universities under Division 2, in 
which ceramics, bakelites, glasses, and various light 
metals were tried, it was concluded that a bullet con- 

pertinent to War Department Project AC-73. 


sisting of a dense material in a plastic binder might 
have the desired qualities of frangibility and resistance 
to firing stresses. 1 ' 7 Arrangements were therefore 
made with the Bakelite Corporation to supply molded 
materials for fabrication into bullets, which were then 
tested for their suitability. The tests included meas¬ 
urement of the limit impact velocity of the bullets 
against a given target metal, their ability to withstand 
loading and firing, and their stability in flight. It was 
decided that a composition designated as Bakelite RD- 
42-93 and consisting of 200-mesh lead powder in a 
thermosetting phenolic-resin binder was the most 
promising, and it was therefore adopted for the pro¬ 
duction of a frangible bullet, subsequently called the 
T44 bullet by the Ordnance Department. The bullet 
produced from the plastic is approximately of the 
same shape as the .30-caliber M2 ball bullet, weighs 
6.95 zb 0.11 g (1.07 zb 1.5 grains) and has a specific 
gravity of 6.93. The ballistic tables for the bullet 

o 

were determined at Aberdeen Proving Ground, and 
the ballistic coefficient on the basis of the T44 Siacci 
functions was found to be 0.163. The bullet may be 
fired through a Springfield rifle or .30-caliber Brown¬ 
ing AC M2 machine gun with a muzzle velocity as 
high as 2,400 fps without showing signs of breakup 
or damage. The limit impact velocity of the T44 bul¬ 
let against Ut-in. 24ST Dural armor plate is 1,750 zb 
20 fps in comparison with 1,390 zb 20 fps for a .30- 
caliber ball bullet reduced to the mass of the T44 
bullet. It was decided, on the basis of the requirements 
for pilot safety involved and the protection that could 
be afforded by the permissible weight of armor on the 
fighter plane, that a muzzle velocity of 1,360 fps was 
allowable for the T44 bullet. This gives ballistic per¬ 
formance such that a sight can be adjusted so that 
the leads (on a reticle diameter basis) required of the 
student gunner can be made practically identical with 
those required in combat with .50-caliber ammunition. 
The maximum practical firing range for the T44 bul¬ 
let as now in use is about 700 yd and the maximum 
contact range is about 600 vd. 

o %j 

A number of variables in the production and use 
of the frangible bullets have been studied. It has been 
determined that variations in the lead-powder filler 
do not produce significant variations in the limit im- 


242 


mmm 


Him 




FUNDAMENTAL INVESTIGATIONS 


243 


pact velocity of the bullets and that considerable 
variation is possible in the time, temperature, and 
pressure during the molding process without appre¬ 
ciably affecting the resulting bullet. Similarly, no 
significant change occurs in finished bullets subjected 
to accelerated aging by heat or cold treatment. No 
difference was found in the limit impact velocity of 
bullets fired at room temperature and at —68 C 
against armor at room temperature. 

On impact against light armor the frangible bul¬ 
lets break into fine particles. High-speed motion pic¬ 
tures show that the bullet disintegrates within 0.19 
msec after impact against Dural armor at a velocity 
of about 1,300 fps. 

In view of the desirability of having as broad a 
basis as possible for selection of the type of frangible 
bullet to be used in production, experiments for this 
purpose were carried out at the Division 2 Ballistics 
Laboratory at Princeton University, in addition to 
those carried on at Duke University. The Princeton 
laboratory made velocity-loss and time-of-liight meas- 
urements for six types of .30-caliber frangible bul¬ 
lets to determine their suitability. One of the bullets 
tested has the shape of .30-caliber M1906 ball and is 
similar to the T44 bullet in current use. Only one of 
the other five bullets tested showed a drag significantly 
less than the T44. This bullet, which had a secant 
ogive and boattail, showed a marked advantage over 
the T44 only for velocities below about 1,200 fps. 
However, this is the velocity range of interest since 
the T44 is fired at a muzzle velocity of 1,360 fps. A 
determination of stability factors and more precise 
time-of-flight measurements over longer ranges are 
necessary to indicate more clearly whether a bullet of 
this type offers a distinct advantage over the T44. 

The Princeton Ballistics Laboratory has also done 
some preliminary work on a .50-caliber frangible bul¬ 
let. The ballistic coefficient G g of this bullet was found 
to be approximately 0.25, which would give an accept¬ 
able “match” with the combat case for types of attack 
other than pursuit curve. However, data obtained for 
the limit impact velocity of the .50-caliber bullet 
against 24ST Dural show that it would not be safe to 
fire this ammunition at the present type of armored 
target planes when using a muzzle velocity as high as 
1,360 fps. 

10.2.2 The Reduced-Range Scheme 

The problem of obtaining hits in aerial gunnery 
requires solution of a problem involving three vectors: 
the bullet-velocity vector, the bomber-velocity vector, 


and the fighter-velocity vector. By suitable reductions 
in all three vectors a reasonable facsimile of combat 
is achieved. The limiting factors are the minimum 
speed of the bomber and the amount of protection that 
the fighter can carry. These resulted in the choice of 
a bullet having a muzzle velocity of 1,360 fps. Ballis- 
tically, the training bullet should match the .50-cal¬ 
iber API-M8 bullet, now used in combat, as nearly 
as possible. 

Perfect scaling is not possible because of the speed 
limitations that have been mentioned. While the 
trainer-bullet velocity is approximately half the com¬ 
bat-bullet velocity, the speed of the bomber can be 
reduced to only about 10 or 75 per cent of its combat 
speed. Higher trainer-bullet speeds would be possible 
only with heavier target protection. The lack of scal¬ 
ing is compensated for by changing the size of the 
reticle sight ring so that the gunnePs leads on a 
“rad” basis, that is, in terms of the radius of the sight 
ring, are the same in training as in combat. 

10 ‘ 2,3 Armor 

Along with experiments to determine a bullet suit¬ 
able for air-to-air firing, certain other problems asso¬ 
ciated with use of the bullet came within the scope of 
this project. One of these is the ability of armor 1,2 ’ 6 ’ 8,9 
of different types to withstand impact of the frangible 
bullet. This was investigated with the view to deter¬ 
mining the type and thickness of armor necessary to 
use in armoring a plane to protect the pilot and essen¬ 
tial plane parts. Different armor plates were compared 
on the basis of their limit impact velocities. b Limit 
impact velocities at normal incidence (90 degrees) 
were obtained for all plates and at other angles of 
incidence for some plates, since certain parts of the 
target plane need only be protected from hits by bul¬ 
lets striking at an angle of 45 degrees or less. 

Three general types of armor were studied: first, 
Dural armor plate of various types (thicknesses 1/16, 
3/32, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, and 3/4 in.) ; 
second, steel armor manufactured by the Jessop Steel 
Company (thicknesses 3/32, 1/8, 5/32, and 3/16 in.) ; 
and third, Doron, which consists of laminated layers of 
closely woven fiber glass bonded with plastic (thick¬ 
nesses of 8/64, 13/64, and 26/64 in.). 

Of the Dural plates tested, Alcoa 24ST and Rey¬ 
nolds .301T were found to be the only types that could 

b The velocity of the bullet that damages a test plate 
sufficiently to produce a scatter pattern of 5 to 10 fine 
perforations on a sheet of 30-lb drug bond paper 6 to 8 in. 
behind the target. 




244 


FRANGIBLE BULLET FOR AERIAL GUNNERY TRAINING 


be used efficiently in armoring a target plane in terms 
of protection afforded and weight of metal. 

Bare 24ST Dural plate is superior to Alclad plate 
of equal thickness. It was also found that, within lim¬ 
its, higher-strength materials, as measured by static¬ 
testing procedures, are superior to those of lower 
strength. Preliminary tests indicate that multiple¬ 
thickness armor is slightly less effective than a single 
sheet of comparable thickness. Low temperature 
(— 50 C) increases the limit impact velocity of 1 /4- 
in. 24ST Dural by about 50 fps for the .30-caliber 
bullet T44, although the armor appears to become 
somewhat more brittle. Temperature cycling has no 
perceptible effect on limit impact velocities. Experi¬ 
ments on firing more than one shot at the same area 
of armor indicate that several single shots fired in 
slow sequence at armor known to resist one such shot 
do relatively little more damage than one shot, but a 
machine-gun burst of an equal or reduced number of 
shots hitting the same spot may perforate the armor. 

The Jessop steel armor is more resistant, on a 
weight for weight basis, than the 24ST Dural armor 
in thicknesses of Dural greater than 0.350 in. In 
lower thicknesses, the Dural is more effective. 

The limit impact velocity of Vs-in. Doron is about 
the same as that of Vs-in. 24ST Dural plate. However, 
the damage inflicted on Doron by impact of bullets 
is so great that the maintenance problem involved 
in using such material in armoring a plane prohibits 
its use. 

Experiments with 5-ply l% 4 -in. multiplate glass 
of the type used around the cockpit of the target air¬ 
plane showed that this provides adequate protection 
against the T44 round, since the limit impact velocity 
of such glass is above 1,900 fps. The second of two 
shots hitting the same small area of the plate with a 
velocity of approximately 1,550 fps can perforate the 
glass, but will not do so if the shots hit as much as 
D /2 in. apart. A sheet of Plexiglas back of 5-ply 
1 % 2 -in* multiple glass increases its limit impact 
velocity, as previously defined, by about 300 fps. 

10 - 2 - 4 Propellant 

One of the difficulties experienced with the T44 
round as loaded in a .30-caliber Ml case was the pro¬ 
curement of a satisfactorily functioning propel¬ 
lant. 1 ’ 9,10 With the relatively low muzzle velocity of 
the round (1,360 fps) only a small powder charge 
(of the order of 0.80 to 0.95 g) is used, and because 
of the considerable air space, relatively low pressures 
prevail during the burning of the powder. 


The primary requirements of a propellant suitable 
for use with the T44 bullet were found to be (1) that 
it have low position sensitivity (as regards its loca¬ 
tion in the case with respect to the primer location), 
(2) that it burn relatively completely, and (3) that 
in firing the round the modified machine gun func¬ 
tion properly. The position sensitivity and approxi¬ 
mate amount of unburned powder remaining after 
firing were determined for a number of different Her¬ 
cules and DuPont powders. It was found that the 
small-grain fast-burning powders leave little un¬ 
burned powder in the gun, but that the muzzle veloc¬ 
ity obtained with them is quite sensitive to the 
position of the powder in the case, whereas the large- 
grain longer-burning powders leave considerable 
unburned powder in the gun but are relatively posi¬ 
tion insensitive. The tests indicate that the require¬ 
ments of low position sensitivity, proper gun function¬ 
ing, and small unburned residue are incompatible in 
the round as used at present and that some compro¬ 
mise must be made. It was felt that, in the light of 
these requirements, DuPont No. 4759 powder was 
the best of those tested. 

Since a wide range of temperatures, varying from 
room temperature to approximately —50 C are en¬ 
countered in the use of the T44 round, the average 
muzzle velocity was determined for nine production 
lots of T44 rounds at 25, 0, and —50 C. The average 
temperature coefficient between 0 and 25 C for the 
eight lots loaded by the Western Cartridge Company 
and St. Louis Ordnance Plant is about 4.5 fps per 
degree centigrade. This value is considerably higher 
than that of the one lot from the Erankford Arsenal 
(temperature coefficient = 2.8 fps per degree cen¬ 
tigrade). 

In firing the T44 production rounds, it was found 
that the standard deviation of the average muzzle 
velocity was frequently greater than the acceptable 
standard deviation of 30 fps. One of the factors that 
might contribute to the deviation was the variation in 
moisture content of DuPont No. 4759 powder. Since 
little information was available on the effect of mois¬ 
ture on this particular powder, experiments were car¬ 
ried out to determine (1) the effect of exposure to 
constant relative humidities on the weight of powder 
and (2) the muzzle velocity obtained with powder 
conditioned at different relative humidities. It was 
found that for powder conditioned two days at a 
relative humidity of 70 per cent subsequent condi¬ 
tioning at 85 per cent relative humidity increases the 



MODIFICATIONS OF PLANE AND ACCESSORY EQUIPMENT 


245 


weight of the powder approximately 0.15 per cent. 
Firing tests show that the average muzzle velocity 
may be expected to decrease about 9.8 fps per 0.10 
per cent increase in moisture content of the powder. 

io .3 MODIFICATIONS OF PLANE AND 
ACCESSORY EQUIPMENT 

10 - 31 The Machine Gun 

The regular .30-caliber AC M2 machine gun will not 
function as an automatic weapon 1,3,8,11 ' 15 when the 
T44 round is fired through it with a muzzle velocity 
of 1,360 fps, since the momentum and muzzle blast 
are considerably smaller than that of the standard .30- 
caliber round. In view of this, two modifications of 
the gun were made, one of which (the piston gun) 
has been found satisfactory under experimental field 
conditions. 

In the piston gun, the muzzle blast is trapped in a 
cylinder-piston assembly and the pressure developed 
gives the barrel and associated parts the required 
energy for automatic operation. The rate of fire of the 
piston gun is influenced by the type of nozzle on the 
gun, but the rate does not vary significantly for small 
variations in powder charge. The dispersion of shots 
on a ground target is considerably less with the modi¬ 
fied piston gun and T44 round than with the .50- 
caliber machine gun and .50-caliber ammunition. 
However, comparable dispersion occurs in air-to-air 
firing. 

Comparison of average muzzle velocities of rounds 
fired through new and used barrels showed that there 
was no significant variation in the average muzzle 
velocity due to difference in barrels. 

10 3 2 The Plane 

The solution to the problem of firing live ammuni¬ 
tion at a real airplane 1 must involve a compromise 
between the weight of the armor that can be put on 
the target plane and the limit impact velocity of the 
bullet used against such armor. Therefore, the de¬ 
cision as to the weight and velocity of the bullet and 
the armoring of the airplane had to be considered 
simultaneously. 

As a first approximation, successful aerial gunnery 
requires the proper solution of a sighting problem in¬ 
volving the bullet-velocity vector, the bomber-velocity 
vector, and the fighter-velocity vector. It appears that 
a reasonable facsimile of combat can be obtained by 
proper scaling or reduction of all these vectors. The 


limit of the reduction factor is set by the lowest speed 
at which it is practical for the bomber to fly. It is 
necessary also to consider the additional weight of 
armor permissible on the fighter plane. Finally, the 
matching conditions between combat and training 
conditions require a bullet with as high a ballistic 
coefficient as practicable. 

In general, the most important type of attack from 
the standpoint of training is the pursuit-curve ap¬ 
proach of the fighter. In such an attack, if firing is 
excluded during and after the breakaway, the sections 
of immediate vulnerability are those surfaces that are 
visible from a cone defined by a solid angle of 12 de¬ 
grees and centered along the line of flight of the air¬ 
plane. The first two types of target planes were 
armored for use solely with pursuit-curve attacks. The 
first consideration was always the complete protection 
of the pilot compartment and the most vulnerable 
parts of the airplane. A secondary consideration was 
the limitation of damage to a minimum. 

Three types of target airplanes have been produced 
to date. The first was an A-20 airplane armored under 
the supervision of the Aircraft Laboratory, AT SC, 
Wright Field. The last two types are modified P-63 
airplanes produced by Bell Aircraft Corporation and 
designated as RP-63-C and RP-63-G. The last type of 
airplane (RP-63-G) was armored so as to be usable for 
other than near pursuit-curve approaches in training 
and also to allow for the possible higher impact veloci¬ 
ties in the B-29 training program. It is not contem¬ 
plated, however, that continued fire will be directed 
against the armored airplane from any angle other 
than those involved in pursuit-curve or near pursuit- 
curve approaches. 

The only difficulty of significance that has arisen 
in connection with the armor protection is an occa¬ 
sional failure of the cooling duct louvers on the RP-63 
type airplane to afford adequate protection for the 
radiator located behind the louvers. A new louver has 
been designed which presumably will solve this prob¬ 
lem. In general, it has not been necessary in field prac¬ 
tice to replace any piece of armor because of excessive 
damage on surfaces where complete protection was 
intended. As far as is known only three pieces of 1- 
in. bullet-resistant glass have been replaced because 
of bullet damage. 

1033 The Hit Indicator 

An essential feature of the target airplane is a hit- 
indicator 1 system. The primary features of the sys¬ 
tem used are as follows: 



246 


FRANGIBLE BULLET FOR AERIAL GUNNERY TRAINING 


1. An impulse pickup placed on the armor plates 
so that an electric impulse is developed by the gauge 
when the plate is struck. 

2. An amplifier unit by means of which the gen¬ 
erated signal is amplified. 

3. A thyratron-controlled trigger circuit and asso¬ 
ciated counter, relay, and lamps for signaling to a 
gunner when a hit has been made and allowing scor¬ 
ing of such hits. 

The installation used in the RP-63-C target air¬ 
planes was furnished, with the exception of the wiring 
of airplane and signal lamp, by the Sperry Gyroscope 
Company. The gunner signal lamp is mounted in the 
cannon tube and may be seen easily within a cone of 
solid angle of about 30 degrees centered about the long 
axis of the airplane. 

The functioning of this installation was somewhat 
unreliable because of spurious triggering and difficulty 
in proper adjustment of the time-delay relays; there¬ 
fore considerable work was done toward designing an 
improved hit-indicator system. The American Time 
Products Company and the Bell Aircraft Corporation 
have designed amplifiers. The Duke project has con¬ 
structed two sets of low-cost pickup units, each of 
which appears to have considerable promise when 
used with proper filters in the amplifier. 

10.3.4 jj ge of Coupled Instructor's Turret 

It became obvious in connection with the broad 
training program being developed for use with the 
T44 frangible bullet that the development or modi¬ 
fication of several accessory pieces of equipment would 
help to improve the training. Thus, it was pointed 
out by Army personnel that it would be desirable for 
the instructor to be able to criticize the student at the 
actual time an attack is made. The best way to do this 
seemed to be through the development of an instruc¬ 
tor’s or slave turret 1 * 16 driven by the student’s turret. 

It was decided that the most immediate solution 
of this problem would result from the adaptation to 
this purpose of the central-station fire-control system 
developed by the General Electric Company [GE] 
and used on B-29 airplanes. In this adaptation, the 
gunner’s turret controls another turret in which an 
instructor may observe the action of the student while 
firing at the attacking plane. An upper-rear turret 
of the B-29 was modified so that it would carry an 
instructor and would reproduce the movements in 
both azimuth and elevation of a Martin turret which 
would be operated by a student gunner. The Martin 
turret was fitted with the necessary selsyn generators 


to enable it to drive the instructor’s turret in proper 
alignment. 

An N8-A gun sight mounted in a dehectometer 
was attached to the sight yoke of the instructor’s tur¬ 
ret. A camera was mounted so that it was possible to 
make photographs and visual observations simulta¬ 
neously. 

Measurements were made to determine the accuracy 
with which this instructor’s turret follows the driving 
turret. These measurements indicate that the accu¬ 
racy of alignment of the two turrets is such that no 
significant errors in the evaluation of the student 
gunner would result. 

Further preliminary work has been done in this 
general connection in arranging a selsyn-controlled 
range system so that the range setting on a comput¬ 
ing sight in the Martin turret is reproduced on a 
computing sight mounted in the instructor’s turret. 
Such a system should also prove of value in the B-29 
training program. 

10.3.5 Modification of K-15 Sight 

Another investigation of equipment accessory to the 
training program involved a study of the possibility 
of modification of the K-15 1 sight for use with this 
bullet. The operation of the K-15 sight was therefore 
studied to determine the feasibility of making a sim¬ 
ple adaptation of it for this purpose. 

The sight and a motion - picture camera were 
mounted on a revolving turntable fitted with a fixed 
pipper. The camera was focused on a semicircular 
graduated scale, and photographs were made of the 
positions of the gyro reticle and the fixed pipper at 
various predetermined rates of rotation and ranges. 
Thus the combat leads developed for various settings 
of the sight can be determined from the photographs. 

The most convenient method of modifying the K-15 
sight for use with the T44 bullet at training speeds 
is by adjustment of the target-span handle (chang¬ 
ing the effective wing span, and therefore the appar¬ 
ent range, of the target plane). The analysis of the 
data showed such a modification feasible if the follow¬ 
ing assumptions are made: 

1. The fighter and bomber velocities are properly 
scaled so that the fighter paths in combat and in 
training are identical. 

2. The fighter flies a lead-pursuit curve so that 
the lead ratio is 1.41 and the tracking-rate ratio is 
0.71. 

It must be pointed out that for pursuit-curve train¬ 
ing, the maximum range for which the sight can be 




RESULTS 


247 


used is about 450 yd on the present basis of modifica¬ 
tion without making changes in the internal electric 
system of the sight. 

The data also revealed that there are time lags in 
the sight which may in some cases prove to be too 
large for the most effective use of the sight in combat 
gunnery. 

104 FIELD TRIALS 

The first field trials 1 of the frangible bullet were 
made using the armored A-20 target plane and a 
YB-40 bomber at Buckingham Army Air Field at 
Fort Myers, Florida. These tests proved the general 
validity of the use of the frangible bullet as a training 
procedure for aerial gunners. The major part of the 
remaining field trials of experimental nature have 
been carried out by the Frangible Bullet Project of 
the Laredo Army Air Field at Laredo, Texas, using 
the A-20 and BP-63-C target planes. 

Some of the general limitations of the frangible 
bullet technique as brought out by field trials are 
listed in the following: 

1. The long time of flight of the present frangible 
bullet, as compared to the time of flight of .50-caliber 
MS ammunition, necessitates large prediction and de¬ 
flection angles which accentuate the errors of all 
sights. The increased time of flight also gives the tar¬ 
get aircraft more time to depart from a given plane 
of action. 

2. The frangible bullet T44 is not stable if shot 
forward from an airplane going faster than 250 mph. 
This may be of concern in future training. This lack 
of stability can be remedied to a large degree by de¬ 
creasing the pitch of the lands in the barrels through 
which the frangible bullet is fired. 

3. The breaking of tips of the frangible bullets 
causes some trouble in gun malfunction. 

105 PSYCHOLOGICAL ASPECTS 

In the course of the development of the frangible- 
bullet technique and in its practical application to the 
training situation, questions frequently arose as to the 
psychological implications 1 of the scaling procedure 
used in connection with it, both with respect to the 
modification of sights and the alteration of plane 
speeds. In an attempt to obtain sound background in¬ 
formation which would help in orienting the program 
in these matters several series of psychological experi¬ 
ments on the development and analysis of gunnery 


skills were run with untrained subjects. Tests were 
made with 61 subjects and involved 350 experimental 
sessions, representing some 23,000 pointing or track¬ 
ing trials. The main types of trials included were 
pointing at a fixed target with variable deflections, 
tracking a moving target, and pointing with continu¬ 
ously varying deflections at a moving target. 

Some of the many points of significance for the 
general gunnery-training problem brought out by 
these investigations are the following: 

1. The desirability of some method, such as the in¬ 
structors or slave turret, for providing the student 
with a knowledge of his errors at the time of training. 

2. Any evaluation of the relative contribution to 
the final overall firing errors attributable in a given 
sight mechanism to, say, tracking versus ranging 
should be based upon performance after training of 
gunners in the use of the mechanism. This would in¬ 
dicate that if it were possible to choose between auto¬ 
matic radar control of one or the other of these func¬ 
tions in the sight, this decision should be reached on 
the basis of trials by gunners trained on the basic sight 
mechanism and the results of such trials should be 
weighed along with engineering and design considera¬ 
tions. 

3. Skill in tracking once acquired through training 
seems to be retained for a period of at least six weeks. 
On the other hand, there is a lack of retention of the 
skill acquired in the case where the student was 
trained to point a machine gun quickly at a target 
and at the same time give accurately a predetermined 
lead deflection away from the target. 

Because of the limitations in number of subjects 
involved in these experiments, the conclusions in¬ 
dicated in the foregoing material must be regarded as 
preliminary in nature. However, they illustrate the 
possibilities of obtaining information of prime impor¬ 
tance to a gunnery-training program from psychologi¬ 
cal experiments on student gunners, provided these are 
carried out with test equipment closely paralleling the 
gunnery situation itself. Such information should 
have important implications not only for the training 
program but in relation to such matters as the design 
and choice of sight mechanisms. 

106 RESULTS 

10 61 Closeness of Matching between 
Trainer and Prototype 

An analysis of the general considerations that will 
result in reasonable matching of the leads used with 




248 


FRANGIBLE BULLET FOR AERIAL GUNNERY TRAINING 


the frangible bullet with those required in combat 
shows that with proper adjustment of airplane veloci¬ 
ties and sight reticle, and for pursuit-curve attacks, 
the match can be made quite satisfactorily . 1,17 ' 21 
Theoretical calculations of leads required of gunners 
firing at the target plane making attacks along curves 
of pursuit show that the leads, on a rad basis, are the 
same in combat and in training if the adjustments 
previously mentioned are made. The types of attacks 
considered were lead-pursuit and pure-pursuit attacks 
against bombers, parallel flight of fighter and bom¬ 
ber, support fire from a bomber formation against a 
fighter attacking a particular plane in the formation, 
and finally, fighter-fighter attacks. 

10 6,2 Status of Project 

The role that the frangible bullet can play in such 
matters as sight design and modification, study of 
aerial tactics, particularly in relation to fire from for¬ 
mations, in fighter-versus-fighter gunnery training 
and in certain naval gunnery-training problems has 
been studied. 1 

The status of the technique in the training of gun¬ 
ners in bombers as of Y-J Day may be summarized as 
follows: 

1. From the small beginning in November 1944 
bullet production rose to a production capacity of 
from 40,000,000 to 45,000,000 per month in August 
1945. 

2. Some 300 armored target airplanes were pro¬ 
duced for training by the spring of 1945. Prior to 
Y-J Day, 450 additional planes with improved armor 


had been ordered ; all but 30 of these were cancelled 
after Y-J Day. 

3. About 11,000 bomber missions, in which some 
12,000,000 rounds of frangible-bullet ammunition 
were fired by student gunners, were flown in the seven 
gunnery-training schools in the United States. 

4. It was stated just prior to Y-J Day that all firing 
from the air in the gunnery program of the Training 
Command would thereafter be with frangible bullets. 

107 POSSIBILITIES AND LIMITATIONS 
OF THE TECHNIQUE 

The limiting factors at present are the minimum 
bomber velocity and the maximum weight of protec¬ 
tion that can be added to existing planes for use as 
targets. Some improvement in the latter is possible by 
the use of specially designed target planes in which 
the protecting armor contributes to the structural 
strength of the plane instead of being simply added 
weight. With such improved protection, bullet veloci¬ 
ties can be increased several hundred fps over the pres¬ 
ent velocities. This will permit closer scaling of plane 
and bullet velocities and reduce the modifications now 
needed in the sight and the compromises in the tech¬ 
nique. 

However, there is a limit to progress in this direc¬ 
tion, due to the fact that combat-plane speeds and 
combat-bullet velocities will continually increase, 
making it increasingly difficult to build target planes 
strongly enough protected to withstand the bullet ve¬ 
locities required for matching. 



PART IV 


PROPERTIES OF MATTER 


ENTIAL 





Chapter 11 


DESIGN OF MODEL SUPERSONIC WIND TUNNEL 


n.i INTRODUCTION 

T he flight velocity of artillery projectiles has 
been for many years well in excess of the velocity 
of sound in air, which is about 1,100 fps. Aerodynamic 
data relating to the flight performance of a projectile 
can be obtained by studying its trajectory, but this is 
a slow and expensive method. In a wind tunnel, the 
projectile may be held stationary, while air is moved 
past it at high velocity, permitting the easy and quick 
determination of the aerodynamic forces acting on the 
model. For this reason, the desirability of a large su¬ 
personic wind tunnel became apparent several years 
before World War II. The construction of such a tun¬ 
nel at Aberdeen Proving Ground was decided upon 
by the Ordnance Department. 3 

However, due to the rather special properties of air 
flow at supersonic speeds, certain of the design re¬ 
quirements for such a wind tunnel were not clearly 
understood. For this reason NDRC contracted 
with the California Institute of Technology in 1941 
to construct a small-scale supersonic wind tunnel, 1 
and in it to study the design and instrumentation 

a Pertinent to War Department Project OD-24 and to 
Navy Department Project NO-3. 


problems connected with the construction and opera¬ 
tion of a large supersonic wind tunnel. The specific 
problems which it was proposed to study were: 

1. The compressor pressure ratios and power re¬ 
quirements at various air speeds. 

2. The method of designing a nozzle to produce 
supersonic flow in the test section. Unlike a subsonic 
wind tunnel, the air speed in the test section of a su¬ 
personic wind tunnel is determined not only by the 
pressure drop through the tunnel, but also by the 
shape of the channel immediately upstream from the 
test section. Analytical methods are available for the 
design of this “nozzle”; it was desired to check these 
and to determine any necessary corrections. Each 
Mach number requires a particular shape and size of 
nozzle. 

3. A method of supporting a model in the test sec¬ 
tion in such a way that the flow around the model re¬ 
mains essentially equivalent to that around the pro¬ 
jectile in free flight. This problem is considerably 
more difficult in supersonic than in subsonic condi¬ 
tions. 

4. Methods of observing the flow around a model 
and of measuring the forces acting on it. These consist 
principally of a schlieren optical system which makes 



\ T FIt>ENTIAl| 


251 






































































































252 


DESIGN OF MODEL SUPERSONIC WIND TUNNEL 



i 0NTIDEXT1AT" 


Figure 2. General layout (vertical section) of supersonic tunnel. Motor and compressor are not shown. 








































































































































































































































PRINCIPAL RESULTS 


253 




<*- 


A 


43 j in. 



visible the density gradients in the air in the test sec¬ 
tion and a balance system on which the model is sus¬ 
pended. 

The small wind tunnel was constructed with a test 
section 2.5 in. square. It was operated through a range 
of Mach numbers from 1.2 to 4.4. (Mach number is the 
ratio of throat-section air speed to the local speed of 
sound.) Sufficient information was obtained on all of 
the above points to permit furnishing definite design 
data for the large supersonic wind tunnel at Aberdeen 
Proving Ground. Figures 1, 2, and 3 give details of 
construction. 


ii 2 PRINCIPAL RESULTS 

The most important results of the above investiga¬ 
tions can be summarized briefly. 

1. In the determination of the pressure ratios neces¬ 
sary to operate the tunnel, it was found that a 
pressure recovery from the test section to the end 
of the diffuser can be effected by an amount compar¬ 
able to that through a normal shock wave. In other 
words, a portion of the kinetic energy of flow at the 
test section can be converted to potential energy or 
pressure, thus diminishing the pressure difference to 
be overcome by the compressor. Curves of compressor 


t'O-VFIDENTIAll 





























































































































254 


DESIGN OF MODEL SUPERSONIC WIND TUNNEL 


pressure ratio versus Mach numbers were obtained. 

2. It was found practical to support projectile 
models by a single strut from the rear. This strut is 
connected to the balance system, which enters the 
channel to the rear of the model. The part of the bal¬ 
ance system in the channel is shielded from the direct 
airstream by a windshield of special shape. It was 
found necessary to expand the channel around the 
windshield at low Mach numbers in order to avoid pro¬ 
ducing disturbances in the flow at the test section. 
Correct combinations of windshield shape and channel 
shape were found at all Mach numbers. A typical 
installation is shown in Figure 4 as viewed with the 
schlieren apparatus at a Mach number of 2.4. 

3. The method of designing nozzles using the 
method of characteristics 2 ’ 3,4 was found to be satis¬ 
factory, although the existence of a boundary layer of 
retarded air along the nozzle walls necessitates some 
corrections. 

4. The presence of walls in the test section does not 
affect the flow around the model if the latter is small 
enough. The permissible size of model depends on the 
Mach number, becoming less as the Mach number de¬ 
creases toward 1. A blunt model 0.33 in. in diameter 
can be used in the 2.5-in. test section down to a Mach 
number of 1.2; below this speed, the problems of 
model size and support system make testing very diffi- 



Figure 4. Schlieren photograph of flow at Mach 
number of 2.4. 


cult if not impractical. The relation of Mach number 
to permissible model size was determined. 

ns CONCLUSIONS 

The practicality and utility of a supersonic wind 
tunnel for investigating problems in ballistic aerody¬ 
namics was demonstrated. Various aspects of the de¬ 
sign and instrumentation problems associated with 
such a wind tunnel were studied and satisfactory so¬ 
lutions found in all cases in the range of Mach num¬ 
bers from 1.2 to 4.4. 






Chapter 12 


BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


12.1 INTRODUCTION 

1 Purpose of Investigation 

xperimental and theoretical investigations of the 
behavior of materials under dynamic conditions 3 
were first undertaken by Division 2 as part of its pro¬ 
gram of fundamental research on the mechanism of 
projectile penetration and perforation. During the 
passage of a projectile through armor the material in 
the vicinity of the penetration receives very severe and 
very rapid distortion. It was believed that a knowledge 
of the effect of deformation rate on the relation be¬ 
tween stress and strain and on the occurrence of brittle 
rupture would be useful in any study of projectile 
penetration. During the progress of the work, various 
ad hoc military applications were made. These were 
generally experimental comparisons of impact 
strengths of materials, e.g., light alloys for airplane 
construction tested at low temperatures, steels to be 
used in underwater plating of naval craft, metal com¬ 
ponents of projectile fuzes, and small crusher cylin¬ 
ders or spheres for measuring explosive pressures in 
guns. A large part of the work was also concerned 
with two fundamental problems: (1) the manner in 
which plastic strain is propagated and (2) the effect 
of impact velocity on mechanical properties of metals. 

12 . 1.2 Previous Investigations 

Experimental Work 

For some time it had been believed that rate of 
straining or rate of stressing of a material has an 
effect on its stress-strain relation and on its resistance 
to failure. In 1904, Hopkinson 1 concluded that a soft 
steel can endure a stress several times exceeding its 
elastic limit without plastic deformation, provided the 
duration of loading is made sufficiently short. More 
recently, so-called notch-impact tests, intended mostly 
as a measure of the brittleness or notch-sensitivity of 
a material (not of the behavior under impact) have 
been much used. A number of investigators have, in 
addition, attempted to study the effect of deformation 
rate on the stress-strain relations of various 
metals. 2 ’ 11 The latest of these researches employed 

“Pertinent to War Department Project OD-57 and to Navy 
Department Projects NO-7, NO-11, and NS-109. 


rotary-type testing machines, 0 ' 11 capable of speeds 
up to about 200 fps and using specimens generally 
similar to standard tensile specimens. In those investi¬ 
gations in which forces were measured during each 
test, it was generally found that the dynamic force as 
a function of deformation was somewhat higher than 
the static force. 8 ' 11 

Theoretical Work 

No analysis of the tensile impact test was attempted 
in the years preceding World War II. The propagation 
of elastic waves in materials was well understood, of 
course, but almost no attention was paid to waves in 
nonlinear media other than gases, which had been 
treated by Riemann 12 in the 1860’s. In 1930, L. H. 
Donnell 13 showed that a longitudinal wave in a wire 
or bar with nonlinear stress-strain relation would sfif- 
fer a continual change of shape due to the unequal 
speeds of the different levels of stress. 

12.1.3 Progress of Work during the War 

A considerable part, but by no means all, of the 
work done in this field during World War II was done 
by Division 2. In the following brief account, the work 
of other agencies will be included in order to give a 
fairly complete if not detailed picture. 

The situation is complicated by the large number 
of organizations involved and by the variety of prob¬ 
lems attacked. Within Division 2, work was done at 
the following laboratories: University of Pennsylva¬ 
nia, Carnegie Institute of Technology, California In¬ 
stitute of Technology, Massachusetts Institute of 
Technology, Westinghouse Research Laboratories, and 
Princeton University. Outside of Division 2, pub¬ 
lished work was done by NDRC Division 18, by 
Watertown Arsenal Experimental Laboratory, and by 
the British, especially at Fort Halstead by the Arma¬ 
ment Research Department [ARD] of the Ministry 
of Supply. The methods of attack were partly experi¬ 
mental, partly analytical. The problems covered may 
be divided broadly between two classes: (1) those 
dealing with the manner in which plastic stress and 
strain are propagated (these received mostly analyti¬ 
cal treatment with experimental verification) and (2) 
those concerned with the manner in which the stress- 




256 


BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


strain relation of a material is affected by the impact 
velocity (these were treated experimentally, but with 
analytical explanation and discussion). 

University of Pennsylvania and Carnegie 
Institute of Technology 

The first work in this field in the division was begun 
in September 1941, at the University of Pennsylvania. 
This project was transferred to the Carnegie Institute 
of Technology in November 1942 and ended in May 
1944. The experimental work consisted in compression 
of small copper spheres and cylinders of the types used 
for determining explosive pressures in guns. Later, 
armor steels were tested. The apparatus consisted of a 
rotary testing machine capable of a peripheral speed 
of 100 fps. Dynamic force-deflection curves were ob¬ 
tained. In addition, theoretical investigations were 
made dealing with the propagation of plasticity in 
the compression-test specimens, with the propagation 
of the plastic zone in a thick plate due to an expanding 
cylindrical hole, and with the effect of an impulse on 
the material of a plate. 

California Institute of Technology 

Work was undertaken at the California Institute of 
Technology in March 1942 and consisted of the 
following: 

1. Tensile impact tests on short specimens (up to 
12 in.) of various metals, mostly steels, in a rotary 
impact machine capable of peripheral speeds up to 
200 fps. The force-time relation during each test was 
obtained. 

2. The development of analytical methods of treat¬ 
ing the propagation of plasticity under impact in 
wires and bars, including the specimens tested in the 
rotary machine. 

3. Experiments on long wires in a guillotine-type 
machine mainly for the purpose of testing the theory 
developed in (2) above. 

4. Pure strain rate tests in which propagation 
effects were eliminated. 

5. Compressive impact. 

6. Rapid loading tests. 

7. Miscellaneous experiments and analyses con¬ 
cerned with lateral impact on plates and beams and 
with perforation of plates. 

In January 1944, the contract with the California 
Institute of Technology was transferred to Division 
18, NDRC. Reference should be made to the STR of 
that division for a discussion of all the experimental 
work (both before and after the transfer) done under 


this contract. The theoretical work is discussed in the 
present volume. 

Massachusetts Institute of Technology 

Experimental investigations of the behavior of met¬ 
als at high strain rates were carried out between July 
and November 1942. The apparatus used consisted 
essentially of a piston fitting a cylinder containing 
explosive. Detonation of the explosive stretched and 
broke the tensile test specimen. These tests were in¬ 
tended only for comparison with those obtained by 
other division contractors and have not been published 
by the division. 

Westinghouse Research Laboratories 

From November 1942 to August 1944, experimen¬ 
tal work on stretching of steel and nylon specimens 
at moderate rates of strain was pursued. These tests 
were primarily concerned with the propagation of the 
zone of yielding in materials having well-defined yield 
points. 

12.2 THE PROPAGATION OF PLASTICITY 

IN SOLIDS 

1221 Plasticity 

A plastic material is one that can be given a perma¬ 
nent deformation by the application and subsequent 
removal of external forces. The stress-strain relation 
of such a material (as obtained by means of the sim¬ 
ple tensile test, for example) is usually curved, but 
with a straight initial portion. The removal of load 
gives an unloading line that is usually straight and 
parallel to the first part of the loading curve (Figure 
1). Generallv similar relations are obtained in other 
kinds of stressing, e.g., simple compression, biaxial 
or triaxial loading, etc. Most plastic materials are 
elastic up to a certain stress, the elastic limit, defined 
as the highest stress that can be reached in a stressing- 
straining cycle without leaving permanent strain. 
Normally, the elastic part of the stress-strain relation 
is linear. 

12 2 2 Elastic \\ aves 

The behavior of elastic materials under static forces 
or under impact is quite well known. For example, 
when a uniform wire or rod receives a longitudinal 
impulsive stress less than the elastic limit, the effect is 
to produce in the specimen a longitudinal stress wave 
which maintains its form and which travels along the 


OOXm>ENTlAT| 





THE PROPAGATION OF PLASTICITY IN SOLIDS 


257 


specimen with constant speed. The speed is equal to 



where E is Young’s modulus, the ratio of stress to 
strain, and p is density, or mass per unit volume 
(weight per unit volume divided by g, the acceleration 
of gravity). Since stress and strain are related, such a 


o- 



wave of stress is simultaneously a wave of strain. The 
stress o-, strain e, and particle velocity I 7 at a point 
of a wave in an elastic medium are related. For the 
uniform bar or wire at a point where the elastic waves 
are all moving in the same direction, the relation is: 



A wave of this type travels unchanged until it meets 
a discontinuity of some kind, such as a fixed end, a 
free end, a change of section, or a change of material 
characteristics. 

At a fixed end or at a free end the wave must be 
reflected totally. In the first case the reflected stress 
wave is exactly like the incident wave except for its 
direction of travel. In the vicinity of the fixed point, 
stress and strain are increased by the combination of 
parts of incident and reflected waves. Particle velocity, 
on the other hand, is diminished in this region due to 
interference of the waves. At the fixed point, stresses 
and strains are exactly doubled and particle velocity 
is exactly zero. At a free end, the reflected stress wave 
is the negative of the incident wave, stress and strain 
being of opposite sign to those of the original wave. 
Particle velocity, however, is in the same direction 
as in the original wave. In the vicinity of the free 
end, there is interference between the two waves in 
respect to stress and strain and reinforcement in re¬ 
spect to particle velocity. Exactly at a free end, the 


particle velocity is doubled, and stress and strain are 
permanently zero. 

12 2 3 Plastic Waves 13 21 

In a plastic material the situation is complicated 
for the following reasons : 

1. There is no longer a linear relation between 
stress and strain; in addition, the relations are dif¬ 
ferent for increasing and for decreasing stress. 

2. A wave does not maintain its form as it pro¬ 
gresses. Rather, the front or region of increasing 
stress tends to become longer and longer, at least in 
normal cases. 

3. The unloading wave travels faster than the wave 
front or loading wave, catches up to it, and tries to 
eat it away. This introduces complications into the 
analysis. 

A wave of stress moving along a uniform member 
can be thought of as a series of very small waves, one 
superimposed upon the other. Each wavelet, of ampli¬ 
tude Ao- and superimposed on a stress a, has a veloc¬ 
ity dependent upon its position in the stress-strain 
relation. In fact, its velocity will be a function of the 
stress or, according to the following relation: 



In this expression da/de is the slope of the engineering 
stress-strain curve at the stress a. Since, in a normal 
plastic material this slope decreases with increasing 
stress, each stress wavelet moves slower than the im¬ 
mediately lower one. The strain at any point of the 
wave front is, of course, that corresponding to the 
stress at that point according to the stress-strain rela¬ 
tion. The stress wavelet Ao- gives rise to an increment 
of particle velocity 

AT 7 = cde. 

Thus, the particle velocity V corresponding to a stress 
cr or to a strain e in the increasing part of a wave 
front is: 



The quantity da/de is obtained as a function of 
either a or e by graphical differentiation of the engi¬ 
neering stress-strain relation. 16 ’ 19 ' 21 Equation (1) 


CONFIDENTIAL 































258 


BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


can be used to obtain the stress and strain resulting 
from a tensile or compressive impact velocity V, pro¬ 
vided the corresponding stress-strain relation is used. 
See Section 12.2.8 below for a discussion of compres¬ 
sive impact. 

12 2 4 Critical Tensile Velocity 

In tension, the engineering stress-strain relation 
becomes horizontal at the ultimate strength of the 
material. If equation (1) is integrated to this point, 
the velocity so calculated is the critical tensile impact 
velocity. It would be expected that tensile impact at 
a velocity exceeding this critical velocity will always 
result in immediate necking and failure, with very 
little deformation away from the zone of necking. At 
velocities less than the critical, rupture may occur 
anywhere in the specimen, after reflection from a 
fixed boundary has occurred, and all of the member 
must participate in the deformation. Thus the energy 
required to break a member in tension is expected to 
be small at velocities above the critical. Experimen¬ 
tally, this conclusion is found to be correct. For most 
ductile materials the agreement between the critical 
velocity calculated according to the static stress-strain 
relation by equation (1) agrees well with that found 
experimentally in either the rotary- or the guillotine- 
type machine. This indicates (1) that the theory of 
equation (1) is at least approximately correct, (2) 
that the static and dynamic stress-strain relations for 
these materials are nearly the same. However, for one 
class of materials, mostly soft steels, which have a so- 
called yield-point at which a finite increase in strain 
occurs with constant or even decreasing stress, the 
agreement between observed and calculated critical ve¬ 
locities is not good. The conclusion is that the static 
and dynamic stress-strain relations differ considerably 
for such materials. This conclusion is supported by 
comparisons of dynamic and static deformation forces 
obtained in rotary machines 0,10 ' 12 and was also 
reached by Hopkinson 1 on the basis of quite different 
experiments (Section 12.1.2). The critical tensile im¬ 
pact velocities of most ductile materials are of the 
order of 100 to 200 fps. 

12 2 5 Reflection of Plastic Waves 

The reflection of a plastic wave at a discontinuity 
resembles generally the reflection of an elastic wave. 
The problem is much more difficult to handle analyti¬ 
cally in the plastic case but has been solved. 22 ' 24 The 
reflection of a stress wave at a fixed end in an elastic 
member gives rise to stresses and strains that are ex¬ 


actly double those in the incident wave. If the mate¬ 
rial is plastic, the maximum reflected stress is less 
than twice and the reflected strain more than twice 
the maximum stress and strain in the incident wave. 

12 2 6 The Unloading Wave 

Normally, a stress wave has not only a front of in¬ 
creasing stress, but also a back part or tail in which 
the stress diminishes to zero. The behavior of the back 
of a plastic wave depends on the unloading stress- 
strain relation of the material. Normally, this un¬ 
stressing relation is linear, but is steeper than the 
major part of the loading or stressing part of the 
relation. Consequently, the unstressing part, or tail, 
of the traveling wave tries to behave like an elastic 
wave and to move with a greater velocity than the 
plastic front. This means that if the member is long 
enough the tail of the wave will always catch the front 
and will tend to pass through it. Such a process is 
not possible; the back of the wave passes partly 
through the front and reduces it somewhat, is re¬ 
flected from it, and returns as an elastic wave toward 
its starting point. At the starting point (the point of 
original impact) this reflected wave is again reflected 
and retraces its way to the more slowly moving plastic 
front. When the plastic front is reached by the new 
unloading wave the whole process repeats itself. At 
every such repetition the intensity of the plastic wave 
front is reduced, until it disappears or is reduced 
to the elastic limit of the material. The portion of the 
member in which this complicated process has taken 
place shows a nonuniform distribution of permanent 
strain. Near the point of impact the strain left in the 
member is that corresponding to the impact velocity 
as given by equation (1). At the point where the rear 
of the wave first overtakes the front of the wave the 
permanent strain begins to decrease and continues to 
decrease to the point in the member where the un¬ 
stressing wave was reflected to the rear. Following this 
there is a short section of the member in which the 
permanent strain is constant; this is followed by a 
section of decreasing strain, then by a short section of 
constant strain, and so on. The stepped distribution of 
permanent strain in a specimen is illustrated in Fig¬ 
ure 2. It is of interest to note that the stepped dis¬ 
tribution of strain was observed experimentally only 
after its occurrence had been predicted from analy¬ 
sis. 16 For a more complete discussion of the behavior 
of the unstressing wave, reference should be made to 
the bibliography. 16 * 22 * 23 


t ONFIDEXTIAi 






THE PROPAGATION OF PLASTICITY IN SOLIDS 


259 




X IN INCHES 


Figure 2. Theoretical (-) and experimental (-) 

and in 80-in. aluminum wire (B and D). 



X IN INCHES 



of strain distribution in 80-in. copper wire (A and C) 


122 7 Analysis of Impact Tests on Short 

Specimens 

As stated above, although tensile impact tests had 
been carried out for several vears before World War 
II there had been no attempt to analyze their re¬ 
sults, it being assumed merely that the force deflec¬ 
tion obtained dynamically gave the dynamic stress- 
strain relation of the material directly. It is now 
known that this assumption is not exactly correct. 
It is, however, possible to use the static stress-strain 
relation in calculating the expected relation between 
force and extension during a test. Any differences be¬ 
tween the calculated and the observed relations can 
be taken to be at least partly due to differences between 
static and dynamic stress-strain relations. Unfortu¬ 
nately, the conditions of loading during a test are 
sometimes somewhat uncertain and may give rise to 
effects that obscure the results of such analyses. Of 
value in the analysis of impact tests is the explanation 
given for the existence and the method of calculating 
the critical impact velocity. Another contribution of 
plastic analysis to the impact tests is in connection 
with the afterflow or continuation of deformation that 
occurs in a tensile specimen after it breaks. Ordinarily 


this effect is small; however, occasionally it becomes 
important . 25 The theory of plastic wave propagation 
has also been used to aid in discussing the significance 
of measurements of energy required to break a speci¬ 
men during the tensile test . 25 

12 2 8 Compressive Impact on a Uniform 

Member 

The analysis of wave propagation in tension applies 
equally well in compression, provided the stress-strain 
relation is of the same form, i.e., concave downward. 
However, for large strains the compressive stress- 
strain curve must become concave upward (due to 
the fact that cross-sectional area increases under com¬ 
pression) and the analysis that has been outlined does 
not exactly apply. Some attempts at solving this prob¬ 
lem have been made . 26,27 In the region where the 
stress-strain curve is concave upward a stress incre¬ 
ment tends to move faster than the stress immediately 
smaller. Thus, a wave front tends to become steeper, 
not flatter, as it progresses. This change of shape can 
continue until an infinite stress gradient exists at the 
wave front. An infinite stress gradient, which may be 
thought of as a wave with a vertical front, then moves 
along the member. This is a kind of shock wave whose 


COXFIDEXTIA]f 






















































260 


BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


characteristics, including speed and the relation be¬ 
tween stress and impact velocity, are known. With in¬ 
creasing impact velocity the impact stress increases 
according to the shock-wave relations just mentioned 
and the material of the member acquires a velocity 
equal to the velocity of impact. However, above a cer¬ 
tain striking velocity this is no longer true because 
the material is not strong enough to acquire the full 
velocity of the impact but tends to slough off sidewise 
against the striking body, while immediately in front 
of this region the member continues to approach the 
striking body. Thus the member behaves partially like 
a fluid. With increasing impact velocity this behavior 
is emphasized more and more until, at a velocity 
equal to or exceeding the speed of an elastic wave in 
the member, the behavior is exactly like that of a fluid, 
the impact pressure being dependent only on the den¬ 
sity of the material and the velocity of impact, and not 
on its strength. In this limiting case, 

(T = P V\ 

This theory has not been verified experimentally 
because of the velocities involved. Compression impact 
tests 28 on fairly long specimens were made at the 
California Institute of Technology project at veloc¬ 
ities up to about 200 fps, and the results are outlined 
in the STR of Division 18. The calculated critical 
compressive impact velocity for a particular annealed 
copper is 600 fps and for hot-rolled 1018 steel, 1,500 
fps. 29 

12.2.9 Transverse Impact on a Thin Wire 

This problem was first treated for the plastic case 
by English investigators, but was also solved at the 
Princeton Station of Division 2. It is found that two 
distinct propagations occur in the wire. There is a 
stress wave propagated as in normal longitudinal 
impact. There is also a kink that moves along the wire 
away from the impact point. In this case also there is 
a critical velocity, above which deformation is confined 
to the vicinity of the point of impact. The critical 
velocity in transverse impact is greater (by a factor 
of 2 or 3) than for longitudinal tensile impact. For 
materials whose tensile strain at the ultimate stress 
is small compared to unity, the following expression 
gives the approximate ratio between the transverse 
critical velocity T\ and the tensile critical velocity 
V of equation (1) : 



In the above expression o-„ is the ultimate tensile 


stress, and p is density (weight per unit volume di¬ 
vided by g, the acceleration of gravity). For the an¬ 
nealed copper of the previous section having a critical 
compressive velocity of 600 fps, the critical transverse 
impact velocity is calculated to be 450 fps while the 
critical tensile velocity is only 160 fps. 

A practical application of this analysis is to the 
problem of the behavior of balloon mooring cables 
when struck by aircraft. (During World War II, cer¬ 
tain German planes were equipped with cable cutters 
on the leading edges of wings.) The critical trans¬ 
verse impact velocities of steels are in the range 250 
to 600 fps and thus are within the range of operating 
speeds of aircraft. 

12.2.10 Behavior of Thin Diaphragms under 

Impulsive Pressure 

If a thin diaphragm receives a sudden impulse of 
short duration it tends to move bodily, with constant 
velocity in the direction of the impulse. However, the 
edges of the diaphragm cannot move and therefore 
give rise to stresses and deformations which are propa¬ 
gated inward with constant speed. Until these reach 
a point on the sheet, that point has not been affected 
by the boundaries and has moved exactly as though 
there were no boundaries. Thus it can be seen that 
immediately after such an impulse a diaphragm has 
a shape resembling a pie plate, being flat over the 
central region and with curved or sloping edges. 
The kink that separates the flat and the sloping areas 
moves inward, diminishing the former and enlarging 
the latter. (This shape occurs for any uniformly dis¬ 
tributed pressure, even if not of short duration.) 

If the diaphragm is long and narrow, the influence 
of the short sides of its behavior can be neglected ex¬ 
cept in their vicinity. Such a. diaphragm when sub¬ 
jected to an impulse (of very short duration) behaves 
exactly like the wire discussed in the preceding sec¬ 
tion except that it is necessary to consider the inter¬ 
action of stresses and kinks from two edges meeting 
at the center. An additional consideration is that the 
stress-strain relation for a member that is unable to 
contract in one dimension (like the diaphragm) dif¬ 
fers somewhat from the normal tensile relation. Thus 
there is a critical impulse for such a diaphragm—the 
impulse that gives it a velocity equal to the critical 
transverse velocity of the material according to equa¬ 
tion (2), making due allowance for the lateral re¬ 
straint. An impulse per unit area exceeding this would 
be expected to cause immediate failure at the 
boundary. 


0 


TIA 





EFFECT OF IMPACT VELOCITY 


261 


The behavior of a circular diaphragm is generally 
the same, but more difficult to analyze. There is a crit¬ 
ical impulse per unit area equal or approximately 
equal to that for the long, narrow diaphragm. Ex¬ 
periments with such diaphragms subjected not to 
impulsive pressure but to suddenly applied, nearly 
constant pressure show clearly that the central part 
of such a diaphragm remains flat until reached by the 
kink coming from the edge. The characteristic shape 
of a dynamically loaded and distorted, but unbroken, 
diaphragm differs markedly from the shape of a 
statically loaded one, being very much more conical. 29 
Identical results are obtained in the case of dia¬ 
phragms subjected to shocks from underwater explo¬ 
sions. (See Chapter 1.) 

It must not be assumed that an impulse smaller 
than the critical impulse will not break a diaphragm. 
The significance of critical impulse is that a greater 
impulse will cause failure at the boundary with very 
little absorption of energy, while smaller impulses can 
result in failure at the center but with considerable 
absorption of energy. 29 

12 211 Lateral Impact on Beams 

This problem has been solved analytically for the 
plastic case and the results found to agree reasonably 
well with experiments. 30 ’ 31 The solution is based on 
that obtained by Bousinnesq 32 for the elastic case. 
Due to the fact that bending is the governing factor 
rather than tensile stress as in the case of the thin 
wire, the results differ considerably from those ob¬ 
tained for the wire. In particular, it is found that for 
a constant impact velocity on a very long beam the 
quantity y/t (deflection divided by time after impact) 
is a function of the quantity x/t 2 (distance from the 
point of impact divided by the square of the time). 
In other words, all deflection curves obtained during 
the first stages of impact at constant velocity on a 
long beam can be reduced to a single curve if deflec¬ 
tions are divided by the time and distances from the 
impact by the square of the time. There is found to 
be an impact velocity below which no permanent 
bending will occur. This depends only on the mate¬ 
rial and the cross-sectional shape of the beam but not 
on its size. Eor structural steel I beams the elastic 
limit velocity is about 25 fps. Over a certain range of 
velocities just above this value, permanent bending 
will occur only in the vicinity of the point of impact. 
Over a range of velocities immediately higher there 
will be two regions of permanent bending (of oppos¬ 
ing curvatures), one under the force, the other mov¬ 


ing along the beam. For still higher velocities there 
will be three zones of permanent bending, etc. 

12 212 Concentrated Impact on Plates 

This problem was attacked both experimentally and 
theoretically in the California Institute of Technology 
project. 33 ' 35 The experiments were made in the 
guillotine-type machine on 14-in. steel plates 7 in., 3 
ft, and 6 ft in diameter, at velocities ranging from 0 
to 200 fps. Two theories were developed, one consider¬ 
ing only plastic bending of the plate, the other ignor¬ 
ing bending strength and considering only tensile 
stresses in the plane of the plate. The experimental 
results appear to lie between the results of the two theo¬ 
ries but somewhat closer to the bending theory. It was 
concluded that any satisfactory theory of the behavior 
of plates under concentrated impact would have to 
involve both bending and extensional effects. 

12 213 Applications of Theory to Penetra¬ 
tion and Explosion Phenomena 

At the Carnegie Institute of Technology there were 
developed analyses applying to the mechanism of 
projectile penetration in thick plates 36 and to the 
effects of an explosion in contact with a plate. 37 In 
the first case, the propagation of stress and deforma¬ 
tion in a very thick plate due to an expanding cylin¬ 
drical hole is studied. This is based on and is an ex¬ 
tension of work dealing with a similar problem in 
which propagation effects are ignored. 38 The second 
analysis deals with the propagation of a plane pres¬ 
sure pulse across the thickness of a plate, with the 
reflection of the pulse on the far side and with the 
spalling that occurs there as a result. 

Some experimental work on the mechanism of 
projectile penetration was carried out at the California 
Institute of Technology. 39 

12 3 EFFECT OF IMPACT VELOCITY ON 
MECHANICAL PROPERTIES OF MATERIALS 

The object of this work was to determine in what 
way and how greatly the mechanical properties of a 
material, such as yield strength, ultimate strength, 
strain at rupture, etc., are affected by the impact ve¬ 
locity at which deformation is produced. Most of this 
work was at very rapid rates of straining in which 
specimens 6 to 12 in. long were broken at velocities 
up to 200 fps. One series of tests was run at much 
lower rates, of the order of a fraction of an inch per 









BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


262 


minute. Nearly all tests were on metals, mostly steels; 
one series employed nylon. The work was almost en¬ 
tirely experimental but with analyses aimed at ex¬ 
plaining or interpreting the experimental results. 

The work was conducted under four contracts, of 
which the largest, at the California Institute of Tech¬ 
nology, was transferred to NDRC Division 18 in 
January 1944. The experimental work carried out at 
the California Institute of Technology both before 
and after this transfer is outlined in the STR of 
Division 18 to which reference should be made. 


12 31 High-Speed Compression Testing 

This work was started under contract with the 
University of 
the Carnegie Institute of Technology in the fall of 
1942. The original purpose was to determine the dif¬ 
ference in the force required to compress copper 
crusher spheres and cylinders by a given amount 
dvnamicallv and statically. Crushers are used for 
measuring the explosive pressures in guns, being 
placed in a cylinder closed at one end and with a 
piston or plunger closing the other end and in con¬ 
tact with the crusher. The far side of the piston is 
connected to the chamber of the gun whose pressure 
is to be measured. Explosion forces the piston against 
the crusher, compressing it by an amount that is 
used as the measure of the maximum pressure in the 
gun. The crushers are calibrated statically and it was 
believed that the static force-deformation relation 
might not be reliable in giving the impulsive force. 
Work was not confined to copper crushers, however; 
specimens of armor steels were also tested. 

Apparatus 


Pennsylvania and was transferred to 


The testing machine 40 ' 44 (Figures 3, 4, and 5) 

consists essentiallv of a heavv steel wheel which is 

*/ %/ 



Figure 3. Top view of high-speed compression machine. 



Figure 4. Side view of high-speed compression machine. 

I 



Figure 5. End view of high-speed compression machine. 


rotated at the desired speed by a %-hp d-c motor. 
Peripheral speeds ranging from about 7 to 100 fps 
are possible, although all tests have been in the range 
between 16 and 60 fps. Near the periphery of the 
wheel are two horns mounted on bearings. Normally, 
these are cocked back within the circumference of the 
wheel but when released by a solenoid trigger they are 
swung out beyond the periphery by two heavy coil 
springs into position for striking and compressing 
the specimen. The hammer is supported between the 
horns and fits into a niche in the wheel when in the 
retracted position. A %-in. notched steel rod passes 
through the hammer and the two horns, holding the 
former in place. The amount of compression of the 
specimen is limited by two adjustable hammer stops 
which are struck by the hammer after the desired 
compression has taken place. The rod supporting the 
hammer is then sheared off at the notches, allowing 
the hammer to be withdrawn from the neighborhood 
of the wheel by two coil springs to which it becomes 
attached upon impact. 


i ' >N K! DEXTfAfi 




































































































































































EFFECT OF IMPACT VELOCITY 


263 


The force applied is measured by a two-crystal 
quartz piezoelectric gauge mounted between the ham¬ 
mer stops. The specimen to be compressed is nor¬ 
mally from % to V 2 in. long and is placed directly 011 
top of the crystal unit. The charge generated on the 
crystals by the compression force is fed into the hori¬ 
zontal component of a cathode-ray oscillograph 
[CEO], giving the spot a horizontal displacement 
proportional to the force. Calibration of the crystal 
and oscillograph is obtained by applying a known 
static force to the crystal and releasing it suddenly, 
at the same time photographing the horizontal dis¬ 
placement of the oscillograph spot. The vertical com¬ 
ponent of the oscillograph trace is the deformation 
of the specimen, being controlled by a beam of light, 
aimed at a photoelectric cell connected to the ver¬ 
tical component of the oscillograph, which is cut off 
by the motion of the hammer during impact. 

Experimental Eesults 

Force-deformation curves have been obtained for 
small-arms copper cylinders, copper spheres, and for 
cylinders of armor steel. In each material the dynam¬ 
ically obtained relation is from 15 to 30 per cent above 
the static relation (i.e., the force required dynamically 
is greater by this amount than the static force to give 
an equal deformation). Furthermore, the dynamic 
curve is not smooth but consists of a series of steps 
presumably corresponding to the successive reflec¬ 
tions of the stress wave at the end of the test speci¬ 
men. 

Table 1 summarizes the results 40 ' 44 obtained for 
0.400-in. copper cylinders of a particular brand. It 
will be noted that the magnitude of the speed effect 
appears to change very little over the whole range of 
dynamic tests, being about 25 per cent. Other brands 
of copper cylinders of the same dimensions as those 
in Table 1 and also supplied by Frankford Arsenal 
were tested and found to give similar results. 


Table 1 . Speed effect in 0.4-in. copper crusher cylinders 
by compression impact, set: 0.12 in.* 


Rate of strain 
(sec -1 ) 

Average ratio of dynamic 
to static stress 

30 

1.25 

470 

1.26 

705 

1.24 

940 

1.30 

1175 

1.28 

1410 

1.28 

1645 

1.29 


*Furnished by Frankford Arsenal. Designation of metal: 1942 P. O. 
42-25501-Lot 2, annealed in October 1942. 


Tests on copper spheres showed much more varia¬ 
tion between similar specimens than did the tests on 
cylinders; there appeared to be a speed effect aver¬ 
aging about 20 per cent. 44 Because of the lack of 
reproducibility of results, spheres appear to be less 
suitable for use as crushers than do cylinders. 

Measurements on specimens of homogeneous armor 
0.375 in. long and 0.171 in. in diameter showed a 
speed effect of between 20 and 25 per cent for strain 
rates up to 1,500 sec -1 . These results were obtained 
during the early stages of the project and are not 
believed to be as reliable as the results on copper. 

Analyses of Tests 

A calculation of the expected force-time relation 
during dynamic compression of copper cylinders was 
made, 41 using the method of analysis based on plastic 
wave propagation that is described in Section 12.2. 
This shows that the force during impact should con¬ 
tain a number of small steps instead of being perfectly 
continuous; these steps are observed in the experi¬ 
ments. The calculated force is found to be smaller 
than the measured force and the amount of this dif¬ 
ference, which is approximately the amount given in 
Table 1, is believed to be due to a difference in the 
static and dynamic stress-strain relations of the 
material. 

A calculation has been made of the amount of addi¬ 
tional deformation produced in a specimen after re¬ 
moval of the dynamic load and due to its own in¬ 
ertia. 45 It was found that this additional flow is 
negligible in situations corresponding to the normal 
uses of copper crusher gauges. 

Tests on Long Specimens 

Compression tests on specimens about 12 in. long 
were conducted at the California Institute of Tech¬ 
nology. These were designed to investigate the propa¬ 
gation phenomena under compressive loading by meth¬ 
ods similar to those used in tension and to attempt to 
correlate the results with analysis. 28 

12 3 2 High-Speed Tensile Testing 

Practically all of the high-speed tensile tests 40 ' 01 
made for the division were carried out at the Cali¬ 
fornia Institute of Technology. Since all experimen¬ 
tal work under this contract is reported in the STR 
of Division 18, to which this project was transferred 
in January 1944, only a brief description of the equip¬ 
ment used and of the nature of the tests will be 
given here. 













264 


BEHAVIOR OF MATERIALS UNDER DYNAMIC LOADS 


Apparatus 

Two types of testing machines were used. One is a 
rotary machine capable of peripheral speeds up to 
about 200 fps and used with specimens up to 12 in. 
long. This machine consists of a large wheel with two 
fixed horns near the periphery. Impact is produced 
by mechanically inserting a yoke directly under the 



Figure 6. Rotary impact testing machine. 


wheel which permits contact of the horns with the tup, 
which is attached to one end of the test specimen. 
The specimen is thereby stretched and broken in ten¬ 
sion, causing the fixed end to exert a force on the steel 
dynamometer to which it is attached. The extension 
of the dynamometer alters the resistance of its wire 
winding. This impresses a potential on a CRO and 
permits recording the dynamometer force as a func¬ 
tion of time. This machine has been used for inves¬ 
tigating the effect of impact velocity on the force-time 
relations of various materials. Figure 6 shows details 
of the rotary machine. 

The other is a guillotine-type machine (Figure 7) 
and is used for specimens of lengths up to several feet 
in tension, for compression, and for lateral bending of 
beams and plates. It is therefore used mainly for in¬ 
vestigating propagation phenomena, although conclu¬ 
sions regarding the impact-velocity effect can be ob¬ 
tained from it as well as from the rotary machine. The 
machine consists of a pair of vertical steel rails be¬ 
tween which slides a hammer attached to very heavy 
rubber bands. A tensile specimen passes through a 
hole in the center of the hammer and has at its lower 
end a steel block too large to pass through this hole. 
The upper end of the tensile specimen is attached to 
the framework of the machine. No measurement of 


the force in the specimen is normally made, although 
such measurements are possible. In making a test, 
the hammer is raised between the guide rails by means 
of a winch, thus stretching the rubber bands. When 
the hammer is released it accelerates rapidly, acquir¬ 
ing a velocity of any amount up to about 200 fps, de¬ 
pending on the distance raised and on the number of 
rubber bands. The velocity at the time of striking the 
specimen is measured electrically. The hammer is 
brought to rest by a braking system attached to the 
rails of the machine. 

12 33 Low-Speed Tensile Tests 

These were carried out at the Westinghouse Re¬ 
search Laboratories and comprised two series of 
tests. 02,63 In the first series, nylon fibers and flat 
strips were stretched at rates ranging from 0.0042 to 
8.70 in. per sec. The specimen gauge lengths were 2 
and 3 in. The object of this series was to study the be¬ 
havior of a material having a very definite yield point 
subjected to various rates of stretching. Such a mate¬ 
rial does not stretch uniformly from the beginning as 
do materials that have no definite yield point. Instead, 
plastic stretching for the full amount of the yield 
stretch first occurs suddenly at one point of the speci¬ 
men. From this section two yield fronts travel toward 
the ends of the specimen. Between them the material 



Figure 7. Vertical impact testing machine. 


























EFFECT OF IMPACT VELOCITY 


265 


has its full yield stretch; beyond them there has been 
no plastic yielding at all. Not until the entire speci¬ 
men has been covered by the advancing yield fronts 
does uniform deformation begin, which continues un¬ 
til necking occurs. This behavior is characteristic of 
mild steels. 

The second series of tests was conducted on the 
mode of yielding of mild steel at rates of stretching 
ranging from 7.3 X 10 -6 to 1.64 X ICC 1 in. per minute. 
The variables studied were eccentricity of loading, 
length-to-width ratio of the specimen, speed of stretch¬ 
ing, and rigidity of the testing machine. 

Certain preliminary work on the propagation of 
yielding in materials having a well-defined yield point 
was carried out at the California Institute of Tech¬ 
nology - . 64 

12.3.4 Pure Strain Rate Tests 

In investigations of longitudinal impact the results 
have generally been expressed as force-time curves 
during stretching, obtained at definite impact veloci¬ 
ties. These results cannot be used to determine the 
effect of rate of straining on mechanical properties, in 
particular on the stress-strain relation, because in 
each test the rate of straining varies over very wide 
limits. Consequently, the results of longitudinal im¬ 


pact tests must be expressed in terms of impact veloc¬ 
ity and not in terms of rate of straining. 

In order to investigate the effect of pure strain 
rate 65 ’ 60 on the properties of materials, special equip¬ 
ment was devised at the California Institute of Tech¬ 
nology in which a tubular specimen was employed. 
Deformation was obtained by means of fluid pressure 
within the specimen. Strain rates up to about 200 in. 
per in. per sec were attained. See also the Division 18 
STR. 

12.3.5 Preliminary Work on Rapid Loading 

Some preliminary tests 67,08 have been carried out 
at the California Institute of Technology on rapid 
loading in contrast with impact loading. In impact 
loading, some particle or section of a structural mem¬ 
ber is almost instantaneously set into motion, whereas 
in rapid loading a particle or section is set into mo¬ 
tion more or less gradually. It has been shown in the 
pure strain-rate tests that the proportional limit of a 
material is increased with increasing rate of strain. 
The work on rapid loading was directed primarily at 
determining the time that a given stress could be 
maintained at a given value when reached rapidly, 
without causing permanent deformation. The prelimi¬ 
nary tests were not conclusive, but indicated the desira¬ 
bility of continuance of the study. 



Chapter 13 


DEFORMATION OF STEEL 

131 INTRODUCTION 

he object of this investigation was to examine the 
behavior of steel, especially armor steels, under con¬ 
ditions somewhat comparable to those occurring dur¬ 
ing projectile penetration, namely, involving large de¬ 
formations and high stresses. 3 Before the initiation of 
this work in the Division it was known that under hy¬ 
drostatic pressures of the order of 300,000 to 500,000 
psi the ductility of ordinary steels is greatly increased 
and that there are measurable increases in superficial 
hardness. 1 Also, it had just been established at the 
Naval Research Laboratory [NRL] that the average 
pressure on the nose of a projectile while penetrating 
armor plate is of the same order. 2 It was therefore 
evident that an adequate understanding of the process 
of armor penetration would have to consider the modi¬ 
fication in the properties of the steel brought about 
by the stresses generated by the projectile; this was 
the reason for the initiation of this investigation. 

1311 Lack of Correlation between 
Ballistic Behavior of Armor and Its 
Ordinary Mechanical Properties 

At the beginning it was hoped that measurements 
of the effect of hydrostatic pressure on the mechanical 
properties of armor plate might afford an immediate 
answer to a question that was at that time of great 
practical importance, and the first measurements were 
directed toward this end. The problem was to explain 
the frequent lack of correlation between the ballistic 
performance of a piece of armor under actual firing 
tests and the ordinary mechanical properties of the 
plate as determined on small specimens cut from it. 
It was hoped that the effect of hydrostatic pressure on 
various properties, such as tensile strength, ductility, 
and hardness, might, by adding new physical proper¬ 
ties to the list of properties already known, make it 
possible to effect a correlation between ballistic be¬ 
havior and the complete set of properties in those 
cases where the correlation was not possible with the 
more restricted set. 

The early measurements were made with this im¬ 
mediate practical purpose in view, but it was some 

a Pertinent to War Department Projects CE-5 and CE-6 
and to Navy Department Project NO-11. 


UNDER HIGH PRESSURE 

time before the measurements could be applied to an¬ 
swering the question directly because of the difficulty 
of obtaining samples of plates that had failed in the 
ballistic test. By the time such samples were obtained, 
so much practical experience had been gained by other 
investigators that the matter was felt to be well un¬ 
derstood and the problem no longer important. The 
apparent lack of correlation between ballistic behavior 
and ordinary mechanical properties appeared only in 
plates that had rather large-scale mechanical defects 
or chemical inhomogeneities. 

1312 Long-Range Significance 

of Investigation 

The principal purpose of the investigation shifted 
therefore from the original one, involving matters of 
immediate practical importance, to one of more long- 
range significance, for it was still obvious that a satis¬ 
factory analysis of the process of armor penetration 
would have to take account of the behavior of the plate 
during penetration. A systematic investigation was 
therefore indicated in which the effect of such vari¬ 
ables as heat treatment and composition, especially 
carbon content, would be determined. Such an investi¬ 
gation was carried out. 

13.2 MECHANISM OF DEFORMATION 
UNDER LARGE HYDROSTATIC PRESSURES 

The deformation of a material is determined by the 
internal stresses. These, in turn, are normally pro¬ 
duced by a set of external loads. The state of stress at 
a given point can be best understood by thinking of a 
very small cube within the body surrounding the 
point. On each face of this cube there acts a stress 
whose direction is not generallv normal to the face. As 
the cube is rotated about the given point of the body 
the stresses on its several faces will, in general, change 
in both magnitude and direction. It can be shown, 
however, that there is one orientation of the cube for 
which the stress on each face is perpendicular to that 
face. The three directions in the body that are perpen¬ 
dicular to the faces of this cube are called the princi¬ 
pal directions at the point, and the corresponding 
stresses on the faces of the cube are the principal 



266 






APPARATUS AND METHODS OF MEASUREMENT 


267 


stresses. Since the cube is very small, the stresses on 
opposing pairs of faces are equal. Hence there are 
three principal stresses at each point of a body. One of 
these is the biggest and another the smallest of all the 
stresses found when rotating the cube about the point 
in consideration. Several particular states of stress 
may be mentioned. In hydrostatic stress not only are 
the three principal stresses at a point equal to each 
other (and have the same sign), but there is no change 
in the stresses acting on the faces of the imaginary 
cube as it is rotated. A uniaxial state of stress occurs 
during the ordinary tensile or compressive test. In 
this case two of the principal stresses are zero and the 
third is equal to and parallel to the stress applied ex¬ 
ternally to the specimen. Any two states of stress can 
be combined simply by superposition. If the principal 
directions are the same in both states or one is in the 
hydrostatic state, the principal directions are not 
changed by such superposition. 

The behavior of a ductile material such as steel un¬ 
der loads is affected by two distinct mechanisms, de¬ 
formation or floiv, and rupture. The deformation of 
a ductile material depends primarily on differences 
between principal stresses, and thus is only moderately 
affected by a superimposed hydrostatic pressure. The 
rupture of such a material, on the other hand, de¬ 
pends primarily on the absolute magnitudes of the 
stresses acting. Consequently, a superimposed hydro¬ 
static pressure will tend to inhibit the rupture that a 
second system of forces tends to produce. 

Thus, if the standard tensile test is used on a duc¬ 
tile material and is arranged so that the whole ap¬ 
paratus can be immersed in fluid under pressure, the 
following results are expected: under small superim¬ 
posed pressures the normal stress-strain relation is 
obtained. If this is represented not in the usual way 
but in terms of true stress and natural strain b the 
relation consists of a straight initial portion (elastic 
region), a curving transition range near the end of 
which necking begins, and a more or less straight final 
portion having a positive slope and ending at the rup¬ 
ture point. The slope of this line is the so-called rate 
of strain-hardening, corresponding to the fact that de¬ 
formation causes an increase in hardness or in resist¬ 
ance to further deformation. The point of rupture is 
the point at which the steadily increasing stress re- 

b The true stress equals the tensile force divided by the 
actual minimum cross-sectional area, not the original area. 
The natural strain is equal to log e A 0 /A, where A 0 is the 
original cross-sectional area and A the area after deformation. 
In plastic flow the ratio of areas is equal to the ratio of 
lengths, since volume is conserved. 


quired for deformation attains the value necessary for 
tensile failure. 

Under a large hydrostatic pressure the relation be¬ 
tween strains and the additional applied tensile stress 
will be nearly unchanged. Slightly increased stresses 
may be required at a given stage of deformation be¬ 
cause of the internal frictional resistance caused by 
the exterior pressure. However, rupture will be con¬ 
siderably postponed. The stress-strain relation will 
then continue to a value of the applied stress exceeding 
the normal rupture stress by an amount greater the 
greater the hydrostatic pressure. In this way it is pos¬ 
sible to attain deformations very much exceeding 
those normally reached in tensile tests. Since very 
large strains occur in the neighborhood of projectile 
penetrations it is desirable to know how much strain- 
hardening occurs, and whether there is a continuous 
increase of stress with deformation or a leveling off 
at some limiting stress. 

13.3 APPARATUS AND METHODS OF 

MEASUREMENT 

9 

The tensile specimen used has a gauge length of 
approximately 0.47 in., a diameter of about 0.180 in., 
and an overall length of 1.10 in. It is mounted in a 
double-yoke mechanism which exerts a tensile force 
on the specimen when the yoke is compressed. This 
assembly is placed in the cylinder of the high-pressure 
apparatus and is completely immersed in the pressure- 
transmitting fluid (f-pentane was used in these tests). 
Within the cylinder there is also an electrical device 
(called a grid because of its shape) for measuring 
the tensile force, and a manganin resistance gauge for 
measuring the pressure. A piston, advanced by a hy¬ 
draulic press, produces hydrostatic pressure in the 
fluid and at the same time compresses the yoke, 
stretching the specimen. The use of spacers between 
piston and yoke or different quantities of fluid permits 
changing the mean hydrostatic pressure. Pressures up 
to 450,000 psi can be reached with the equipment 
used. 

The pressure and the force on the specimen are 
measured electrically during a test. The distortion of 
the specimen can be determined from the movement 
of the piston after making corrections for the deforma¬ 
tion of the mechanism. In addition, the final dimen¬ 
sions and shape of the specimen are recorded at the 
end of a test. From these data are obtained the stress- 
strain relations under hydrostatic pressure. It should 


■tOXflDENTIAI* 








268 


DEFORMATION OF STEEL UNDER HIGH PRESSURE 


be noted that during necking of the specimen the 
strain along the specimen cannot be determined from 
the total extension, since the strain is not uniform. 
Consequently, only the strain at the end of the test, 
when measurements can be made in the open, is 
known. Thus a series of points below the necking 
point and a single arbitrary point beyond can normally 
be obtained from a single specimen. 

Tests of superficial hardness, one-sided compres¬ 
sion, and punching shear were also made in the ap¬ 
paratus just described by substituting suitable mecha¬ 
nisms for the yoke. 

More detailed descriptions of the equipment and 
technique are given elsewhere. 1 - 3 > 8 > a - b > c 

13.4 test program 

1341 Tensile Tests 

In all, 35 different steels, mostly armor plate, were 
tested in this program. Nearly 350 individual tests 
were made. These are divided into five series described 
below. 

First Series 

In this series, 3 56 tests were made on 24 different 
Navy, armor steels, all ballistically satisfactory. 
Nearly all of these tests were made either at atmos¬ 
pheric pressure or in the highest pressure range pos¬ 
sible, namely, 300,000 to 450,000 psi at the end of a 
test. A number of specimens were cut with different 
orientations in the original plate, in order to allow 
investigation of the effect of orientation on behavior. 
Second Series 

In this series, 4 four types of Navy armor (two of 
them included in the first series), all ballistically sat¬ 
isfactory, received 36 tests. This series was tested at 
hydrostatic pressures ranging from atmospheric to 
about 225,000 psi. The effect of specimen orientation 
with respect to the original plate was examined more 
extensively than in the first series. 

Third Series 

In this series, 5 62 tests at hydrostatic pressures 
ranging from atmospheric to 200,000 psi were made 
on four Navy armor steels, one of which had been 
tested before. Two of the new plates were not accept¬ 
able ballistically. 

Fourth Series 

In this series, 6 49 tests were made at hydrostatic 
pressures ranging from atmospheric to 400,000 psi on 
samples of four Navy armor steels of inferior ballistic 
performance. 


Fifth Series 

In this series, 140 tests were made as follows: 10 
on a 0.34C steel as received, 62 on a 0.45G steel in 
seven different heat treatments and as received, 8 
tests on a 0.68C steel as received, and 60 tests on a 
0.90C steel in six heat-treatments and as received. 
These were made at hydrostatic pressures ranging 
from atmospheric to 400,000 psi. The object of this 
series of tests was, of course, to determine the effect of 
variation of composition and heat treatment of steels 
on their behavior under large hydrostatic pressures. 0 

1342 Hardness Tests 

These tests 3,4 were made only during the early part 
of the work, since it was felt that the change of super¬ 
ficial hardness with pressure (in the Brinell scale, 
roughly 5 per cent for a pressure increase of 150,000 
psi) was too small to be important in the present state 
of penetration theory. Hardness tests were made on 16 
different Navy armor steels that were also included in 
the tension program. 

1343 One-Sided Compression Combined 

with Hydrostatic Pressure 

The apparatus was completed just before the end of 
the contract under which this work was performed. 
Consequently, tests were made on only one type of 
steel. 6 

13.4.4 Punching Combined with 

Hydrostatic Pressure 

These tests were performed at hydrostatic pressures 6 
ranging from atmospheric to 225,000 psi on three 
heat treatments each of the 0.45C and 0.90C steel used 
in the last series of tension tests. 

13 4 5 One-Sided Compression of Steel to 
Large Strains (without Hydrostatic Pressure) 

Tests were made on three specimens cut in mutually 
perpendicular directions from one piece of armor 
steel. 7 These were compressed to a final length ap¬ 
proximately 5 per cent of the original length. 

135 RESULTS 

13.5.1 Phenomena Investigated 

The measurements were aimed primarily at investi¬ 
gating two different aspects of the effect of pressure 
on tensile phenomena. The first aspect embraces the 

c See Table 1 and Figures 1 to 5 of this chapter for details 
of treatment and results of the tests of the 0.45C steel. 


• !->N m hkntiaQ 






RESULTS 


269 


phenomena of strain-hardening which occur before 
rupture in the region of plastic flow. The second as¬ 
pect covers the phenomena of rupture. In general, dif¬ 
ferent types of measurement were made for the two 
kinds of phenomena. In the study of strain-hardening, 
several specimens were stretched by different amounts, 
allowing the flow stress to be determined as function 
of strain. The flow stress is closely connected with the 
so-called true stress defined as the total tensile force 
divided by the cross-sectional area of the neck. This 
true stress should more properly be called the average 
true stress, because the stress is not constant across 
the section, but varies by virtue of the deviation of the 
neck from a straight cylindrical contour, the degree of 
departure of the stress from uniformity being greater 
the greater the curvature of the contour at the neck. 
The method ,of correcting the true stress for this lack 
of uniformity so as to obtain the significant flow stress 
has been discussed in detail elsewhere . 5 ’ 9 

Relation Between Flow Stress and 
Strain in Tension 

When flow stress is jflotted against natural strain 
(Section 13.2), an approximately linear relation is 
found at stresses above that at the initiation of neck¬ 
ing. By performing the experiment under hydrostatic 
pressure it is possible, because of the very much 
greater range of strain attainable under pressure with¬ 
out fracture, to establish this relation with much 
greater accuracy than would be possible from meas¬ 
urements made at atmospheric pressure only. To a 
first approximation, the relation between flow stress 
and strain is independent of the hydrostatic pressure 
under which the experiment is made, and the results 
have usually been represented on this basis. Recently, 
however, in some work done at Harvard University 
for the Watertown Arsenal the accuracy of the meas¬ 
urements has been sufficiently increased to disclose a 
small effect of pressure on the relation between flow 
stress and strain, the flow stress for a given strain be¬ 
ing slightly increased by pressure. 10 

Phenomena of Fracture 

The second aspect of tensile phenomena under pres¬ 
sure, fracture, itself presents two aspects; the first is 
the way in which the strain at which fracture occurs is 
affected by pressure, which may be expressed otherwise 
as the effect of pressure on ductility; and the second is 
the change in the geometrical appearance of the frac¬ 
ture with pressure. The effect of pressure on ductility 
may be exhibited graphically by plotting the strain at 


fracture against the hydrostatic pressure at the instant 
of fracture. The geometrical character of fracture is in 
general complicated, but at least one aspect of it lends 
itself to numerical representation. At atmospheric 
pressure the fracture of the steels studied here is us¬ 
ually of the cup-cone type. The bottom of the cup is 
sharply enough defined in these experiments to per¬ 
mit measurement, and the fracture may be character¬ 
ized by the ratio of the area of the tensile part to the 
total cross-sectional area of the break. 


Table 1 . Schedule of heat treatments applied to 
0.45C steel. 


No. 

Description 

Temp. (F) 

Time (hr) 

1 

Normalized 

1650 

Yz 

2 

Annealed, fine-grained 

1500 

Yz 

3 

Annealed, coarse-grained 

1900 

Yz 

4 

Brine-quenched, 

1500 

Yz 


spheroidized 

1300 

10 

5 

Brine-quenched, 

1500 

Yz 


tempered 

600 

1 

6 

Brine-quenched, 

1800 

Y 


tempered 

600 

l 

7 

Brine-quenched, 

1500 

Yz 


tempered 

900 

1 


13 5 2 Effect of Hydrostatic Pressure on 

Tensile Properties 

As illustrations of the effects discussed in this sec¬ 
tion Figures 1 to 5 are presented. 6 These show the re¬ 
sults of measurements made on samples of a medium 
carbon steel (composition: 0.45C, 0.83Mn, 0.016P, 
0.035S, 0.19Si) that had received the various heat 
treatments listed in Table 1. 

Ductility 

The largest effect of hydrostatic pressure is on duc¬ 
tility; at pressures of 350,000 to 450,000 psi the elon- 



NATURAL STRAIN AT FRACTURE 


Figure 1. Effect of hydrostatic pressure on ductility of 
0.45C steel with heat treatments listed in Table 1. 


CONJT DENTIAH 
























270 


DEFORMATION OF STEEL UNDER HIGH PRESSURE 


gation tolerated at the neck of a tension specimen may 
run to hundredfolds. At these extreme elongations the 
specimen loses its geometrical regularity and the situ¬ 
ation becomes dominated by adventitious factors such 
as the presence of minute inclusions in the steel. In the 
region of less extreme elongations, that is, up to natu¬ 
ral strains of 4 or 5, corresponding to elongations of 
50- or 100-fold, the strain at fracture usually increases 


less, while the ductility of cast iron is not appreciably 
increased by the pressures that have been tried. 

Strain-Hardening 

Strain-hardening can be pushed much further un¬ 
der hydrostatic pressure than at atmospheric pressure 
because of the much greater strains possible without 
fracture. For all the steels that have been studied in 



NATURAL STRAIN 

0 40 63 78 87 92 95 97 

CORRESPONDING REDUCTION OF AREA IN PER CENT 

Figure 2. Flow stress versus strain for 0.45C steel with heat treatments listed in Table 1. Note that slopes of lines, 
i.e., rates of strain-hardening, are to a first approximation the same. 


linearly with hydrostatic pressure, although excep¬ 
tions have been found in which the increase was more 
rapid than linear. 6 The rate of increase of ductility 
appears to be greater for the softer steels; among 
those that have been studied in the present program 
the increase of natural strain at fracture caused by a 
pressure of 150,000 psi may be as much as 2 or as 
little as 0.8, as shown in Figure 1. Other steels are 
known for which the increase in ductility is much 


this investigation the flow stress is approximately a 
linear function of the natural strain, at least up to 
strains of 3 or 4, and is approximately, but not en¬ 
tirely, independent of the hydrostatic pressure 10 
(Figure 2). The rate of increase of flow stress with 
strain is in general greater for the harder steels, al¬ 
though there are examples of crossing of the curves 
not to be explained by experimental error. However, 
the rate of increase for the harder steels is not greater 






















RESULTS 


271 


in proportion to the absolute values of flow stress. 
Thus the flow stress of a typical soft steel may in¬ 
crease from 100,000 to 300,000 psi or by a factor of 
3 for a strain increase of 3; whereas a harder steel, 
e.g., treatment 5 of Figure 2, increases from 250,000 
to 550,000 psi, or by a factor of 2.2, for the same range 
of strain. 

Flow Stress at Fracture 

By combining the results of the two previous para¬ 
graphs it can be concluded that the flow stress at frac¬ 
ture is a linear function of the hydrostatic pressure 
prevailing at the moment of fracture (Figure 3). The 
rate of increase of flow stress at fracture shows less de¬ 
pendence on the nature of the steel than do the factors 
from which it is derived; as a rough average, there is 
an increase of flow stress at fracture of 300,000 psi for 
an increase of hydrostatic pressure of 375,000 psi for 
any value of the flow stress. 

Orientation of Specimens 

With respect to the orientation of the specimen in 
the original plate, the following appears to be true. 
The flow properties, which determine the form of the 
stress-strain relation, appear to be the same for all 
orientations. However, the rupture strength is less for 
specimens taken perpendicular to the original surface 
of a plate. For such specimens fracture occurs at 
smaller elongations and lower stresses than for speci¬ 
mens taken in either of the directions parallel to the 
plate surface, between which there appears to be no 



Figure 3. Relation between flow stress at fracture and 
hydrostatic pressure for 0.45C steel with heat treat¬ 
ments listed in Table 1. This figure is obtained b}* 
combining curves of Figures 1 and 2. 

difference. The differences between different directions 
with respect to fracture phenomenon become smaller 
at higher pressures and probably disappear above 
250,000 psi. 

Effect of Pressure on Flow Stress 

The method of these experiments has not been ac¬ 
curate enough to permit a satisfactory study of the 


o 

< 

o 

_i 


ID 


X 

< 


CO 

CO 

UJ 

a: 

H 

co 


UJ 

O 

< 

a: 

UJ 


> 

< 



Figure 4. Ordinate is calculated by dividing total load at maximum by original cross-sectional area and multiplying 
by 1.221, which corresponds to assumption that initiation of necking occurs at strain of 0.2. Average stress at maximum 
load is essentially the “tensile strength.” 


XT I A t 












































272 


DEFORMATION OF STEEL UNDER HIGH PRESSURE 


effect of hydrostatic pressure on plastic flow in the 
initial region of small strain', before the initiation of 
necking, i.e.. up to the maximum load. The effect of 
pressure on the maximum or the so-called tensile 
strength ha-, however, been established (Figure 4). 
It appear^ that the flow stress at the maximum load 
increases linearly with the hydrostatic pressure, and 
the amount of increase, with a few exceptions, is ap¬ 
proximately the same for all steels, independent of the 
a: '"lute 'tress. The flow stress at the maximum load 
increases by approximately 20.000 to 25.000 psi for 
an increase of hydrostatic pressure of 450.000 psi. 
Thus the magnitude of this effect is much less than 
that of any of the other effects that have been 
mentioned. 

The I'tre^s at which plastic flow first begins seems 
to be increased by pressure by approximately the 
amount by which the flow stress at maximum load 
is increased. 

Appearance or Fracture 

The appearance of the tensile fracture 1 11 varies 
with pressure. Practically all the steels that were 
studied in this program show the normal cup-cone 
type of fracture at atmospheric pressure. With in¬ 
creasing hydrostatic pressure the tensile part of the 
break, that is, the bottom of the cup. occupies a pro¬ 
gressively smaller part of the total cross section, and 
entirely disappears at a certain pressure beyond which 
the fracture is entirely by slip along curved shear 
surfaces 1 Figure 5 ). 5 Up to the pressure at which the 
tensile part vanishes the ratio of the tensile part of 
the area to the total area is roughly a linear function 
of pressure. Figure 5 shows several exceptions to this 
rule, in which the tensile part of the fracture per- 



HYDROSTATIC PRESSURE AT FRACTURE IN PSI 

Figure 5. Effect of hydrostatic pressure on type of 
fracture obtained in tension. Ordinate shows ratio 
between area of tensile portion of break and total 
cross-sectional area. 


.fists to higher pressures than would have been extra¬ 
polated from measurements only at lower pressures. 
In general, the pressure at which the tensile area dis¬ 
appears is higher the harder the steel. 

io.o.o Effect of Hydrostatic Pressure on 
Superficial Hardness 

This question was examined only in the earlier tests 
of this program. 3 4 For the samples of 16 types of 
Xavy armor tested the effect of a pressure of 150.000 
psi was to increase the Brinell hardness by an amount 
which fluctuated irregularly around 5.7 per cent. 
The effect is obviously not large and presumably is 
related to the increase in plastic flow stress in tension 
that is caused by pressure. Because this effect is com¬ 
paratively small, it was not studied further. 

Effect of Hydrostatic Pressure 
on Flow under One-Sided 
Compression Stress 

This study was only barely started in this pro¬ 
gram. Numerical values have been obtained for one 
armor-plate steel. For plastic shortening up to 10 
per cent, hydrostatic pressure appears to increase the 
compressive flow stress linearly and by about the same 
amount as the increase of stress at initial plastic yield 
in tension or as the increase of Brinell hardness. 

13 ° 5 Effect of Hydrostatic Pressure on 
Behavior under Punching Forces 

This phenomenon 6 has been studied only for the 
three softest heat treatments of the 0.45C’ and 0.90C 
steels used for the tensile program, at pressures up 
to 225,000 psi. The effects are similar to the effects of 
pressure on tensile behavior in that there is a great 
increase in ductility. As the pressure is increased, the 
punched material has to be forced through greater 
distances before it breaks clear; at the higher pres¬ 
sures there is a gradual disappearance of the phe¬ 
nomena of fracture until eventually, as shown bv other 
tests at pressures somewhat higher than those used 
here, the punching may be moved through the entire 
thickness of the plate without loss of coherence. 
Strain-hardening is an accompaniment of the punch¬ 
ing process. This strain-hardening is of the same 
order of magnitude as would be expected front a crude 
comparison with the strain-hardening in tension. The 
total force required to start the plastic movement of 
the punched disk also increases with pressure by the 
,'ame order of magnitude as the corresponding tensile 

























RESULTS 


273 


effect. The work required to expel the punched disk is 
greater by 25 to 30 per cent at pressures of 200.000 
psi than at atmospheric pressure. 

13 - 5 - 6 Compression of Steel under Simple 
Longitudinal Stress to Lar^e Strains 

The method of Taylor and Quinney, 12 amounting 
to compressing in stages with reshaping between 
stages to minimize the extraneous components of 
stress arising from friction, was applied to an armor- 


plate steel to produce a final compressive natural 
strain of 3. or reduction of length to 5 per cent of the 
original. After the initial stages the true compressive 
stress rises linearly with natural strain. This is un¬ 
like the behavior of copper for which the true com¬ 
pressive stress approaches a constant value for large 
strains. 7 The rate of strain-hardening of this steel 

c 

in simple compression is somewhat less than its rate 
in simple tension, and the absolute values of flow 
stress in compression are less than in tension. 


* 







PART V 

PROTECTION 





Chapter 14 


DEFENSE AGAINST SHAPED CHARGES 


INTRODUCTION 

he fact that hollow explosive charges (desig¬ 
nated shaped charges for security reasons) can 
defeat thick steel plates or other protection has long 
been known; however, no attempt was made to make 
military use of this fact until the beginning of World 
War II, when all combatants introduced weapons 
employing this principle. Artillery shells of various 
calibers and rocket-propelled projectiles for antitank 
work were encountered most frequently. Large demo¬ 
lition charges for defeating concrete fortifications 
also appeared. Though many of these weapons were 
ineffective because of faulty design, improvements 
were made rapidly. A joint Army-Navy-NDRC Com¬ 
mittee on Shaped Charges, organized to study and 
promote the use of hollow-charge weapons in early 
1943, considered the threat great enough do warrant 
setting up a project to study countermeasures. a,b 

A shaped-charge weapon consists essentially of a 
hollow liner of inert material, usually metal or glass, 
and of conical, hemispherical, or other shape, backed 
on the convex side by explosive. A container and a 
detonating device are included (Figure 1). When det¬ 
onation occurs the liner is compressed against itself, 
giving rise to a jet of metal or glass particles moving 
outward along the axis of the liner at very high ve¬ 
locities. This jet is able to achieve great penetration 
into any near target. 

The performance of the hollow-charge projectile 
differs from that of other projectiles in that the 
thickness of material it can perforate is essentially 
independent of its striking velocity. In fact, hand- 
placed charges may perform somewhat better than 
the projectile type because they can be more readily 
detonated at the best distance from the target sur¬ 
face. Hand-placed hollow charges have been used 
against both tanks and concrete fortifications. The 
fact that performance is independent of velocity and 
therefore of range would appear to make these charges 
ideal for antitank artillery. However, when hollow- 
charge projectiles are caused to rotate by the rifling 
in the guns frcmi which they are fired, their perform¬ 
ance drops 30 to 50 per cent against solid homoge¬ 
neous armor and much more than that against spaced 

a Pertinent to joint Army-Navy Project AN-1. 

b See Data Sheets 3A5 and 3A6 of Chapter 19. 


armor or low-density targets. Nonrotated fin-stabilized 
hollow charges can be made to perform as well when 
fired dynamically as when they are fired statically. 
This accounts for the popularity of rocket-propelled 
low-velocity projectiles such as the American and 
German bazookas. These weapons are light, easily 
constructed, and remarkably effective. They can be 
carried by infantrymen almost as easily as rifles and 
under good conditions can perforate and set on fire 
any tank. If these weapons had been well designed 
at the beginning of World War II, they would have been 
a serious menace. 

14,11 The Experiments 

Since the static performance of a hollow charge 
always equals or surpasses its performance when fired 
dynamically, it was decided to start the search for 
protective devices using a small charge of standard 
construction that could be detonated statically. Al¬ 
though liners of various shapes and materials were 
being used, a charge employing the steel-cone liner 
(with 1%-in. base diameter, 42° cone angle) of the 
M9A1 rifle grenade was adopted, partly because these 
cones were available in large quantities and partly be¬ 
cause steel cones were being used in the majority of 
weapons. Pentolite (50 PETN/50 TNT) was adopted 
for the explosive. 

The experiments were devised with two purposes 
in view; first, to determine the effectiveness of mate¬ 
rials or combinations of materials that gave promise 
of providing low-weight protection; and second, to 
investigate the fundamental laws governing the pene¬ 
tration and perforation process. The division was not 
sharp between these two types since most experiments 
contributed to both programs. 

142 THEORY OF JET PENETRATION 

Figure 1 shows a cross-sectional view of the head of 
an American bazooka which contains a typical hollow 
charge. When this weapon strikes a target, the base 
fuze, operating on the inertia principle, detonates the 
charge from the rear. A detonation wave travels for¬ 
ward and collapses the steel-cone liner, starting at its 
apex. The collapse of the cone squirts forward a long, 
narrow jet of steel at velocities from 10,000 to 30,000 





277 



278 


DEFENSE AGAINST SHAPED CHARGES 



Figure 1. Head of American bazooka showing typical 
shaped charge with conical steel lining. 


fps. 1 ' 13 This process is illustrated by the series of 
high-speed radiographic photographs 8,14,10 in Fig¬ 
ure 2. The photographs were taken of detonating 
charges in various stages and are arranged to show 
the sequence of events in one charge. The last pic¬ 
ture shows a jet perforating some steel plates. Early 
in the process of its formation, the jet breaks up into 
fin e particles but retains its jetlike characteristics 
out to great distances. There is a gradient in the ve¬ 
locities of the particles along the jet, the particles in 


front moving faster than those at the rear. 9,10 This 
causes the jet to lengthen and reduces its average 
density with time. 

When a jet strikes a target of armor plate or mild 
steel, pressures of around a quarter-million atmos¬ 
pheres are produced at the point of contact. These 
pressures are so far above the yield strength of steel 
that the target material flows out of the path of the 
jet as would a fluid. There is so much sidewise mo¬ 
mentum associated with the flow that the diameter of 
the hole produced is considerably larger than that of 
the jet and depends mainly upon the strength of the 
target material, since the radial flow of the material 
is eventually stopped by the strength of the target. 
Thus a larger hole is made in mild steel than in 
armor plate. However, the depth of penetration into 
a very thick slab of mild steel will be only slightly 
greater than that into homogeneous armor. 



Figure 2. Series of high-speed radiographs showing conical steel linings of shaped charges in progressive stages of 
collapse, to illustrate formation of jet and slug. Last of the series shows jet from one such liner after perforation of 
two steel plates. (Aberdeen Proving Ground photographs.) 
























THEORY OF JET PENETRATION 


279 


As the jet particles strike they are carried off radi¬ 
ally with the target material. Thus the jet is used up 
from the front and becomes shorter and shorter until 
finally the last jet particle strikes the target and the 
primary penetration process stops. The actual pene¬ 
tration continues for a short time, especially in weak 
targets, because the kinetic energy imparted to the 
target material by the jet must be dissipated. The 
additional penetration caused by this afterflow is 
called secondary penetration. Its magnitude depends 
upon target strength. It is mainly responsible for the 
small differences observed between the depths of 
penetration in mild steel and in homogeneous armor, 
although there is probably some difference in the 
primary penetrations as well. 

Since the pressures produced by the jet are much 
greater than the yield strengths of most target mate¬ 
rials, both the target and the jet can be considered 
as fluids in calculating the rate of penetration. Simple 
hydrodynamic theory shows that the rate of penetra¬ 
tion is proportional to the jet velocity. However, the 
rate at which a given length of jet is used up is also 
proportional to the jet velocity. Thus the depth of 
penetration is almost independent of jet velocity. This 
supposes, of course, that the low-velocity jets are 
nevertheless able to produce such high pressures that 
the hydrodynamic theory holds. Though the faster 
jets do not produce deeper holes, they produce wider 
holes than the slower jets. The depth of primary pene¬ 
tration P' is obviously proportional to the length of 
jet /, since the length determines how long the pene¬ 
tration process will last. Since primary penetration 
is nearly independent of strength, the process is con¬ 
trolled only by inertia, which depends upon the den¬ 
sity p of the target and the average density pj of the 
jet. Actually, the primary penetration P' is propor¬ 
tional to c 



c The point of contact of a fluid jet with the target moves 
through the target at a velocity U. If the jet has an absolute 
velocity V, its velocity relative to this point is V — U. The 
pressure at this point due to the jet is the same as that due 
to the target material, which has a relative velocity U toward 
this point. Thus, by Bernoulli’s theorem 

i »(V-U)*=yw or = 

But primary penetration equals the penetration velocity U 
times the time of penetration l/(V — U ), 



where l is the length of the jet. 


An increase in standoff increases the length of jet 
l and decreases the average jet density pj, while - the 
product of the two quantities remains substantially 
constant. Therefore, from the above equation it ap¬ 
pears that the primary penetration increases with 
standoff. However, due to slight asymmetries and ir¬ 
regularities in construction of charges, which vary 
from charge to charge, the jets waver and spread some¬ 
what. This effect tends to reduce the effectiveness of 
the jets, but only at large standoffs. Consequently, at 
small standoffs an increase in standoff improves per¬ 
formance, while for large standoffs the reverse is true. 
There is an additional reason for the rapid increase 
in penetration as the charge is moved away from near 
contact with the target. The jet changes character as 
it travels away from the charge. When the jet first 
emerges from the liner, its density is near the density 
of the liner and it behaves like an incompressible 
fluid. Hence, at the point of contact with the target, 
the jet spreads out and its force is exerted over a wider 
area than the original jet cross section. On the other 
hand, at large standoff the jet separates into widely 
spaced particles which do not affect each other and 
which suffer no radial spreading until after they strike 
the target. The total force is thus concentrated on an 
area equal to the jet cross section. 

Armor can be protected from shaped-charge attack 
by covering the armor with a material that will use 
up the jet before it strikes the armor. The rate at 
which the jet is used up is proportional to \/ p, where 
p is the density of the target material. If low-density 
materials are used for protection, they must be made 
thicker than those of higher density. However, lower 
total weight of protection is provided with loiv-density 
materials. In fact, the weight of the protection re¬ 
quired against a given weapon is roughly proportional 
to \/p. For example, if the density of the material 
used to provide protection against a given weapon is 
reduced by a factor of 4, the thickness must be ap¬ 
proximately doubled and the weight can be approxi¬ 
mately halved. For practical reasons it is not advisable 
to use materials having densities much lower than 
twice that of water. 

When low-density materials are used to protect 
steel, the residual penetrations into the steel can 
be calculated approximately from the fact that the 
reduction in penetration caused by a slab of given 
thickness is proportional to the square root of its den¬ 
sity. A more reliable method makes use of the curve 
of residual penetration into steel versus standoff of 


CONFIDENT! 










280 


DEFENSE AGAINST SHAPED CHARGES 


the weapon. This curve, a characteristic of the weap¬ 
on, must be known in order to achieve reliable results. 

14.3 EXPERIMENTAL PROGRAM 

Experiments on the general problem of protection 
against shaped charges were started in August 1943, 
and by October 1943 a plastic armor (gravel with a 
pitch-mastic binder) had been found that was much 
lighter than the homogeneous armor required for 
equal protection. In cooperation with the Flintkote 
Company, which made the plastic armor, a series of 
tests was started which improved this protection and 
further reduced its weight. A wide variety of aggre¬ 
gates was tried, of which pure quartz gravel in a 
mastic of pitch and wood flour proved best. This was 
designated HCR2. At the same time a series of tests 
was planned and carried out, mostly at the Aberdeen 
Proving Ground, d to determine whether or not prac¬ 
tical use could be made of this material against exist¬ 
ing weapons. Some tests were made on models of ship 
structures and these were supplemented by a test 
carried out on a larger scale at the Norfolk Navy 
Yard for the purpose of investigating this means of 
providing ships with protection against torpedoes 
having shaped-charge warheads. However, it seemed 
improbable that this type of torpedo attack would 
become serious in World War II and the project was 
dropped. It appeared that shaped-charge weapons 
could be most effectivelv used against tanks and there- 
fore the protection of tanks was the major problem. 
Shaped charges were also being used to neutralize 
concrete fortifications. The protection of concrete 
structures was considered next in importance to the 
protection of armored vehicles. 

1431 Tank Protection 

The problem of protecting tanks 1 ’ 17 ' 27 was made 
difficult by the fact that the Germans (probably with 
their own heavily armored Tiger tank in mind) had 
started using bazookas and new shaped-charged 
weapons called Panzerfausts, the latter capable of 
perforating 8 to 10 in. of armor plate, while the tanks 
in use by the American Army could be defeated by 
weapons capable of perforating only 2 in. of armor. 
To complicate the problem further, the American 

d Some tests were also made at the NDRC Division 8 
Explosives Research Laboratory, Bruceton, Pennsylvania, and 
one early test was made by the Armored Board at Fort Knox. 


tanks could stand very little additional weight. The 
thickness of protective material was also limited by 
the requirement that tanks must be able to pass over 
Bailey bridges. The German decision to use large 
charges probably saved many casualties, for in order 
to make the charge large they had to sacrifice muzzle 
velocity which made their weapons so inaccurate that 
it was very difficult to hit a tank even from close 
range. Probably because of this fact, Allied tank 
losses to shaped-charge weapons were so light that 
the necessary tests at Aberdeen were given a low pri¬ 
ority, reducing considerably the progress made on the 
protection problem as a whole. 

Plastic Armor for Tank Protection 

The original plan for protecting tanks called for a 
set of small steel panels filled with plastic armor 
(HCR2) that could be fastened to the outside surface 
of any M4 tank in an emergency. It was hoped that 
by making the panels small the area damaged by a 
direct hit from any type of projectile would be small; 
that is, the damage would be confined to one or two 
of the panels. Tests at Aberdeen showed that: 

1. HCR2 panels are very effective against artillery- 
type hollow-charge projectiles that are stabilized in 
flight by rotation. 

2. HCR2 panels are less effective against nonro- 
tated fin-stabilized projectiles, especially when these 
are fuzed to explode close to the surface. While steel 
is defeated most easily by shaped charges that explode 
to standoffs of 1 or 2 calibers, HCR2 is defeated most 
easily by those that explode close to the surface. 

3. Many of the shaped-charge weapons found in 
the field are capable of larger penetrations than re¬ 
ports had indicated. 

4. The HCR2 must be contained in large and 
strong steel panels to prevent excessive damage by 
projectiles. A heavy face plate is needed to prevent 
high explosive [HE] and high-explosive antitank 
[HEAT] shells from penetrating into the panels and 
blowing them apart. 

This information could only be obtained by making 
tests at a proving ground where facilities were avail¬ 
able for trying all types of projectiles. It could not 
have been inferred from laboratory tests. 

The new information showed that, considering the 
weight of the HCR2, the steel panels, and the fasten¬ 
ing devices, from 8 to 12 tons are required to protect 
the M4 tank adequately against the largest enemy 
shaped charge, the Panzerfaust. It is estimated that 
7.1 tons on the heavy tank M26 will provide the same 


I • tv FIDE XT] \f, 








EXPERIMENTAL PROGRAM 


281 


protection against shaped charges as 11.7 tons on the 
Ml. The weight of the protection added is only 16 
per cent of the total on the M26 as compared to 31 
per cent on the Ml. The thickness of panel on the 
turret is only 10% in. on the M26 compared to 13% 
in. on the Ml. e 

For the Ml tank this added weight seemed exces¬ 
sive, but it was the best solution available and it was 
decided to make up a set of panels for test. The work 
of designing the panels was carried out by the Flint- 
kote Company in cooperation with the Office of the 
Chief of Ordnance in Detroit, Michigan. An Ml tank 
with the new horizontal suspension and a wide track 
was sent to Rutherford, New Jersey, to enable the 
Flintkote Company to fit panels to it. The track and 
suspension system of this vehicle is capable of carry¬ 
ing much heavier loads than is the narrow track and 
the vertical suspension used in early models. De¬ 
mountable panels, to be filled with HCR2, made en¬ 
tirely of homogeneous armor plate welded together, 
were designed with %>-in. sides and %-in. face plates. 
The construction of these was onlv partially com- 
pleted by the end of World War II. 

The design and construction of panels that could 
be easily mounted and removed, and at the same time 
withstand combat conditions, turned out to be an 
engineering problem that took a great deal of time. 
In the meantime, reports began coming in that more 
and more Allied tanks were being lost to enemy shaped 
charges. Therefore, a type of panel was designed that 
could be made up in a few weeks, using %-in. mild 
steel instead of homogeneous armor. The face plate 
was strengthened by placing 2 in. of 2-IST aluminum 
alloy directly in back of it, that is, between the face 
plate and the HCR2. Tests with the standard charge 
had indicated that a few inches of aluminum in this 
position in the panels would improve the shaped- 
charge protection as well as offer a means of improv¬ 
ing the ballistic properties of the panels. These pan¬ 
els were fastened to the tank by cables to absorb 
shocks. One set was completed and was tested just 
after World War II ended. It was found that with 
some modification this set of panels would be quite 
satisfactory, although it is believed that the armor- 
plate panels would be more satisfactory. 

e These weights and thicknesses are based upon the latest 
information obtained from statistical studies on the perform¬ 
ance of these weapons. Less than 10 per cent of the largest 
weapons, the Panzerfausts, should come within an inch of 
perforating the basic armor protected by HCR2 even at normal 
incidence. The panels made and tested were somewhat thinner. 


Spikes pop Tank Protection 

As soon as it was discovered that excessive weight 
of any kind of armor would be required to provide 
protection to the M4 tank, a search was started for a 
different principle of protection. Since the Panzer- 
faust and most other weapons detonate very close to 
the surface, and since no shaped-charge weapon func¬ 
tions well if its liner is distorted, spikes that would 
perforate the windshields and the liners were con¬ 
sidered. After many disappointments, a design of 
spikes was found that could be expected to defeat all 
existing shaped-charge weapons 1,18 although fairly 
effective weapons could be developed specifically for 
use against this design. It would add only 3.2 tons to 
the M26 tank and 4.1 tons to the M4 tank, including 
the %-in. armor plate to which the spikes would be 
welded. 

The final design for defeating all weapons was not 
tested, but the designs that were tested and proved 
successful against the various weapons were close 
enough to it to leave very little doubt as to its effi- 
ciency. This design calls for spikes made of 1-in. 
diameter rod, rolled from armor-plate alloy and hard¬ 
ened to Brinell hardness number [BHN] 400. The 
spikes have blunt points and are welded to armor 
plate in a pattern made up of equilateral triangles, 
2.5 in. between centers. The spikes are 7.5, 8.0, 8.5 in. 
long, arranged so that no two adjacent spikes have the 
same length. The staggered lengths make it possible 
to defeat smaller-diameter projectiles with a given 
spacing. When a small-diameter projectile strikes a 
spike pattern normally and midway between two 
spikes of equal length, a slight symmetrical distortion 
of the liner is produced which does not greatly re¬ 
duce its penetrating power. However, with spikes of 
unequal lengths, no such difficulty is encountered. 
The spike pattern weighs much less and takes less 
space than the I4CR2 panels. It is less vulnerable and 
probably will not need to be changed when weapons 
with greater penetrating power are produced. At 
present it appears to be the best solution. 

It has one limitation, however, in that a shaped- 
charge projectile designed with a nose fuze sensitive 
over a wide area would be able to defeat spikes on 
panels. 

1432 Concrete Fortifications 

Fairly large shaped charges have been used to 
neutralize pillboxes and other concrete fortifica¬ 
tions. 1,28 ' 31 These have generally been hand-placed 
charges of large diameter; large artillery shells could 


lOXFIDEXTIAL 









282 


DEFENSE AGAINST SHAPED CHARGES 


also be used. The Corps of Engineers requested a study 
of the problem of making concrete structures that 
would be better able to withstand such attacks. 

Based upon designs furnished by the Corps of Engi¬ 
neers, a long series of small-scale model tests was per¬ 
formed. The effect of increased strength of concrete, 
air spaces in the concrete, scab plates at the rear, 
and face plates on the front were all investigated. 
The weight of concrete needed for protection can be 
reduced by each of these devices. However, the effects 
are rather small, so that the most economical solution 
appears to be the use of more concrete. The scab plate 
is very practical for other reasons, since it greatly 
reduces the spalling due to perforation. 

14.3.3 Weapon Data Sheet 

In the course of this work data were collected, and 
so far as possible correlated, on the design and per¬ 
formance of Allied and enemy shaped-charge weap¬ 
ons. There is a vast variety of designs. Liners are 
conical (with apex angles from 20 to 80 degrees), 
hemispherical, parabolic, and made of combinations 
of these shapes. They are constructed of a variety of 
metals and sometimes of glass. Many different explo¬ 
sives are used; those having high detonation veloc¬ 
ities are preferred; the shapes and degrees of confine¬ 
ment of these explosives vary widely. The method of 
fuzing varies and affects performance. Unfortunately, 
the available information was, and still is, scanty and 
unreliable. Data Sheets 3A5 and 3A6 of Chapter 19 
allow estimates of the performance of shaped-charge 
weapons. 

14.3.4 Standard Charge Improvement 

The performance of individual weapons varies 
widely even when they are selected from the same 
lot. These variations, mentioned in Section 14.2, 
make it difficult to obtain reliable information on 
the protective qualities of different materials and 
devices. If a more consistent charge were developed 
it would help greatly in such experiments. 


In cooperation with the DuPont Eastern Labo¬ 
ratory and the Delaware Ordnance Depot, an attempt 
was made to develop more consistent standard 
charges. 1,32,33 The primary purpose of this research 
was to create a better tool for making protection ex¬ 
periments, although the study was also worth while 
for indicating how much improvement in performance 
is possible through improved construction. 

Out of every lot of standard charges two or three 
were fired as controls. X-rays of the control charges 
revealed that all had flaws or air pockets. Statistical 
comparison of the photographs with the performance 
of these charges indicates that nonsymmetrical flaws 
are more detrimental than symmetrical ones. How¬ 
ever, the correlation was not good enough to justify 
more definite conclusions, since other factors are as 
important as the flaws. For the next series of standard 
charges a new mold was made in which the liner could 
be very accurately aligned. The performance of this 
series was superior, especially at large standoff, and 
analysis showed that the average waver of the jet was 
reduced by about 40 per cent. Attempts were also 
made to improve the consistency of the standard 
charges by carefully selecting the steel for a series of 
cones from one heat of steel. Decarburizing the steel 
cones was also tried. Neither of these appeared to pro¬ 
duce significant improvement. All of the cones used 
in standard charges were made by a mass production 
drawing process and were not as perfect as desired. 
It was evident that if the cones were accurately made 
and accurately aligned in the mold, and if the charge 
could be cast without flaws (especially eccentric- 
flaws), the performance of these charges could be 
made much more consistent. 

1435 Statistics 

Since consistent charges were not available, it was 
necessary to develop a statistical method of treating 
the results obtained with the charges available. The 
methods developed and used are treated in detail 
elsewhere. 1 ’ 33 


'CONFIPEXTIAf, 








Chapter 15 


STRUCTURAL PROTECTION 


15-1 INTRODUCTION 

P rotection can be classified, somewhat arbitrarily, 
as being either civilian or military protection, al¬ 
though many structures can be placed in both cate¬ 
gories. Most considerations applying to one class 
apply also to the other. The difference is mostly in 
dimensions and in function. Military structures may 
run to greater thicknesses than do civilian although 
there is considerable overlap. Military structures are 
generally designed to resist several different forms of 
attack, namely, blast, fragmentation, earth shock, 
shaped charge, and attack by high-explosive [HE] or 
armor-piercing [AP] projectiles. Not all forms of 
attack may be important in one situation, but normal¬ 
ly more than one must be considered. Civilian protec¬ 
tive structures, on the other hand, are mainly intended 
to give protection against blast, fragments, or debris. 
Furthermore, civilian protection must include con¬ 
sideration of means of strengthening or otherwise 
protecting existing structures or installations. 

At the beginning of World War II, protection had 
very high priority since there was considerable un¬ 
certainty whether or not attacks would be made on 
the American continent. As World War II progressed 
and it became more and more apparent that no such 
attacks were to be expected, protection became less 
important. This does not mean that protection will 
not be of very great importance in the future. In fact, 
if there is another war, this country must he prepared 
for early attack. Presumably, such attack will be di¬ 
rected at centers of production, communication, and 
government. The problem of preparing adequate pro¬ 
tection for the essential functions and for the popula¬ 
tions of such potential targets should be given high 
priority, not when the danger of attack becomes ap¬ 
parent, but from now on. 

The original concern of Division 2, and its principal 
concern until 1943, was with defense. As World War 
II proceeded emphasis shifted gradually and continu¬ 
ously to attack. This change of interest caused only 
comparatively minor changes in projects. Certain 
kinds of work, particularly that dealing with the 
properties of materials, became relatively less impor¬ 
tant than before. Certain new projects dealing with 


the performance or with the effectiveness of specific 
weapons or with the possibilities of enhancing their 
performance were added to the Division. However, 
most of the work of the Division was equally useful in 
defense or attack. 

This chapter describes those parts of the program 
of the Division that are concerned with protection or 
defense and that are not discussed elsewhere in this 
volume. Brief references will be made to such discus¬ 
sions whenever necessary for completeness. The fol¬ 
lowing chapters of this volume contain information 
especially pertinent to the present chapter: Chapter 
3 on explosions in earth; Chapters 6, 7, 8, and 9 on 
terminal ballistics of armor, concrete, plastic protec¬ 
tion, and earth; Chapter 14 on defense against shaped 
charges; Chapter 16 on target analysis and weapon 
selection; and Chapter 19 on data sheets on effects 
of fire, impact, explosion. The following subjects are 
discussed in the present chapter: the damage to con¬ 
crete structures from contact explosions; damage to 
light structures from blast, especially internal blast; 
experiments on the impact behavior of reinforced con¬ 
crete beams; theoretical analyses of the behavior of 
structures and structural elements under impact and 
blast; applications of the information acquired to 
problems of structural protection; and recommenda¬ 
tions for future investigation. 

15-2 EXPERIMENT 

A very extensive series of tests was conducted by 
Division 2 and the Committee on Passive Protection 
Against Bombing [CPPAB] (later the Committee on 
Fortification Design [CFD]) on various aspects of 
protection. The terminal ballistics of armor, concrete, 
plastic protection and earth was studied at the Prince¬ 
ton University Station. The effects of explosions on 
concrete structures were investigated at Princeton and 
at Camp Gruber, Oklahoma, in collaboration with the 
Army Corps of Engineers. The protection of concrete 
structures against shaped-charge attack was studied 
at Carnegie Institute of Technology in cooperation 
with Division 8, NDRC. Tests on the behavior or rein¬ 
forced concrete beams under impact were made at the 
University of Illinois. 



284 


STRUCTURAL PROTECTION 


15 2,1 Effects of Blast 

In addition to the very extensive series of transient 
measurements of the various phenomena of blast and 
blast propagation that are discussed in Chapter 2 of 
this volume, some studies of the effect of blast on 
structures have been made. 

Static Detonation Tests of Wood-Frame 
Dwelling Houses 

Three typical small wood-frame dwelling houses 
were constructed by the Corps of Engineers at Aber¬ 
deen Proving Grounds and subjected to the effects of 
500-lb general-purpose [GP] bombs (containing 
60/40 amatol), detonating in the air and under 
ground, and to the effects of 250-lb very lightly cased 
TNT charges (equivalent in explosive weight to 500- 
lb GP bombs), detonating in air. 1 The tests were ana¬ 
lyzed by the CPPAB and members of Division 2. 
Transient measurements of blast pressure and dis¬ 
placements were made. The air-blast detonations were 
at distances from houses ranging from 500 down to 
25 ft. The below-ground detonation (there was only 
one) occurred at distances ranging from 17.5 to 60 ft 
from the three houses. 

The following conclusions were drawn. 

1. Extensive damage to similar structures can be 
expected at distances less than 30 ft from either 
ground shock or air blast, the former being slightly 
more serious. Chimneys were never damaged by blast, 
but were susceptible to earth shock. Cement-block 
basement walls fail badly due to earth shock. Other 
types of foundation walls, e.g., solid concrete, might 
be somewhat superior although no great difference is 
likely. 

2. Despite very severe damage on the side of a 
structure facing an explosion there was never serious 
collapse, although considerable sagging occurred. This 
is very significant since most of the casualties pro¬ 
duced in HE attacks on Britain and Germany were 
due to structural collapse. This would naturally be a 
much more common occurrence with the brick bear¬ 
ing-wall construction, so universal in Europe, than 
with the wood-frame construction of the houses of the 
present tests. On the other hand, the protection 
against fragments afforded by the wooden houses is 
somewhat less than by the 12- to 18-in. brick walls 
common in Europe. 

3. The frequent collapse of chimneys because of 
earth shock suggests that home shelters should not be 
located near chimneys. 


Confined Blast 

In order to supplement the measurements of tran¬ 
sient pressures resulting from the detonation of 
charges in confined spaces 2 that are discussed in 
Chapter 2 of this volume, other experiments on the 
damaging power of such confined explosions were car¬ 
ried out at Princeton. The structure in which these 
tests were made had a reinforced concrete floor, roof, 
and columns. It was about 6.5 ft square and 4 ft high; 
thus it was approximately a y 3 scale model. The in¬ 
terior was completely enclosed by brick filler walls, 1 
course thick bonded to the concrete structure on bot¬ 
tom and sides, but not at the top. 

The charges consisted of 22 and 44 g of tetryl and 
were detonated at the center of the enclosed space. 
The deflection of one wall was recorded as a function 
of time during each test. Damage was evaluated at the 
end of each test. In addition, V 2 - and 1-lb charges of 
TNT were exploded outside the structure at 3 ft from 
the center of a brick wall. 

The 44-g tetryl charge at the center of the chamber 
blew out one wall completely and the major portions 
of the others. Analysis of the record of motion indi¬ 
cates that the wall accelerated during the first 35 
msec following the explosion, at which time the cen¬ 
ter displacement was about 2 in. After that the ve¬ 
locity remained essentially constant. This deflection, 
and corresponding interval of time, are believed to 
correspond to complete disruption of the wall, at 
which point much of its ability to confine the gas 
would have disappeared. The 22-g charge caused 
cracks in all walls that essentially destroyed their 
strength, but did not blow any wall out. Following 
this, the external detonation of V 2 - and 1-lb charges of 
TNT 3 ft from the centers of already cracked brick 
walls showed no appreciable additional effect, thus 
illustrating the ability of confinement to enhance the 
effect of blast. Finally, a ^4-lb charge of TNT deto¬ 
nated within the structure, completely wrecking it. 

The corresponding full-scale effects are the follow- 

in or - 

1. One and a quarter pounds of explosive within a 
similar structure 12 ft high and 20 ft square, with 
12-in. brick walls, would cause serious wall cracking. 

2. Two and a half pounds would blow out the walls 
but would not injure the frame, although detonation 
in contact with the floor would certainly injure it. 

3. Fifteen pounds would cause complete destruc¬ 
tion. 

4. Thirty pounds of TNT detonating outside at a 


COX F I DEXT1A EJ 






EXPERIMENT 


285 


distance of 10 ft from a wall would not injure it seri¬ 
ously. 

These conclusions are limited in their applicability 
by two factors; first, most structures have openings of 
one kind or another that permit venting and reduce 
the degree of confinement; second, by the fact that the 
single-course brick wall of the model test is not exactly 
similar to a 12-in., 3-course wall. Whether the 1-course 
wall is weaker or stronger is difficult to decide, al¬ 
though it is believed to be stronger so far as bending 
as a whole is concerned. 

15.2.2 Underground Explosions 

Extensive tests on massive buried reinforced-con- 
crete structures, representing elements of fortifica¬ 
tions were carried out at scales ranging from 1 / 5 to 
full, and are discussed in Chapter 3. The full-scale 
target was a concrete box 25 ft square in plan and 17V2 
ft deep without floor or roof. The side walls of the 
full-scale structure ranged in thickness from 2.1 ft 
to 5 ft. The charge used in the full-scale tests was 
1,000 lb, corresponding to the effect of a 2,000-lb GP 
bomb. Charges were detonated at distances ranging 
from contact to where only minor damage resulted. In 
another series of tests, scaled targets with floor and 
roof were exposed to contact explosions. The largest of 
these structures was 47 ft square and 28 ft high, with 
walls ranging from about 10 to 13.5 ft in thickness 
and with a 9.5-ft roof. At the same time a very exten¬ 
sive series of measurements of the transient phenom¬ 
ena that accompany an explosion in earth was made in 
order to facilitate extension of the results obtained to 
situations not exactly similar to those of the tests. 

Relations between damage, structural characteris¬ 
tics, distance of explosion, type of soil, and amount of 
charge have been determined and are given in Chapter 
3, where these investigations are fully discussed. A 
method of analysis for predicting the effect of an un¬ 
derground explosion on a massive buried target has 
been developed that gives results of the same order as 
those observed. This is described in Section 15.5.2. 

15 2 3 Contact Explosions on Concrete 

In addition to the investigations of the effects of 
explosions on massive, buried concrete structures de¬ 
scribed in Chapter 3, and to the studies of the addi¬ 
tional cratering caused by the explosion of projectiles 
after partial penetration of concrete slabs that are dis¬ 
cussed in Chapter 7, certain more or less fundamental 
studies of the mechanism of crater formation in con¬ 


crete, and of the factors that control it, were made 
jointly by the CFD and Division 2 at Princeton. The 
factors that were investigated are the kind of explo¬ 
sive, the shape of charge and point of initiation, the 
closeness of contact with the concrete surface, and the 
strength of the concrete. In connection with this pro¬ 
gram, the relation between the impulse exerted by ex¬ 
plosion of a contact air-backed charge and the size and 
shape of the charge was obtained from an impulse 
pendulum constructed for this purpose. Some investi¬ 
gations of the effect of using spaced slabs and of em¬ 
ploying a scab-mesh (without concrete cover) to con¬ 
trol scabbing were made. 

Scabbing 

The phenomenon of scabbing 3 consists in the violent 
separation of a mass of material from the opposite face 
of a plate or slab subjected to an impact or impulse. 
The scabbing due to impact of a projectile on a con¬ 
crete slab is discussed in Chapter 7, while scabbing 
caused by contact earth-backed detonation is described 
in Chapter 3. The scabbing that is produced in a con¬ 
crete slab by an air-backed explosion is discussed here. 
Scabbing is undoubtedly due to the propagation of a 
compression wave from one face to the other, and its 
subsequent reflection as a tensile wave. A material 
that is weak in tension, like concrete, may be unable 
to withstand the stresses produced, causing large 
pieces to be thrown off with considerable velocity. No 
complete analysis of the mechanism of scabbing has 
been made; such an analysis would not be entirely re¬ 
liable because the behavior of brittle materials under 
tension is somewhat unpredictable in that consider¬ 
able variation may occur from one test to the next. 
The tendency to scab decreases rapidly with an in¬ 
crease in slab thickness, and, of course, increases with 
an increase in the amount or effectiveness of the 
explosive. 

For concrete of about 4,000-psi compressive 
strength, the scabbing limit for ^-lb TNT demolition 
blocks (l^xl^xdli-in.) standing on end and in¬ 
itiated at the top is approximately 8 in. For the same 
blocks lying flat the limit thickness is about 10 in. 
This difference is due to the greater impulse exerted 
by the flat charge. By use of the model law discussed 
in Chapter 3, it is possible to predict the limit scab¬ 
bing thicknesses for similar charges of TNT (or an 
equivalent explosive) of other sizes. Thus, for end-on 
and side-on detonation, respectively, 

T e = 0.8517*, (1) 

and T = 1.0 WK (2) 


CONFIDENTIAL 






286 


STRUCTURAL PROTECTION 


In these expressions T is the scabbing-limit thickness 
in feet for concrete of normal strength (about 3,000- 
4,000 psi) and If is the weight of charge in pounds, 
having about the same proportions as the demolition 
blocks. For other proportions, interpolation or extra¬ 
polation is necessary. This can probably be done most 
safely in terms of the impulse of the explosions, as¬ 
suming for example that the scabbing limit depends 
only on the impulse produced. On this assumption, 

T = 0.2./*, (3) 

where T is scabbing limit in feet and J is the impulse 
caused by the explosion. This quantity is discussed in 
Section 15.2.4 and methods of predicting it are given. 
It must be pointed out, however, that the relation be¬ 
tween thickness and impulse that is shown has not 
been verified, and is offered only for want of anything 
better. The relation between scabbing limit and con¬ 
crete strength has not been determined; it is believed 
that the limit thickness does not vary greatly with 
changes in strength. 

The scabbed volume is shallower and broader than 
the front-face crater. Its volume in a 5-in. slab sub¬ 
jected to end-on detonation of Mz-lb demolition blocks 
was from four to six times that of the crater. The 
presence of earth, or other backing material, in con¬ 
tact with the rear slab face tends to prevent scabbing. 

Control of Scabbing 

Scabbing of the interior of a concrete structure from 
impact or contact explosion is usually less serious than 
would be the penetration of the same missile and its 
subsequent confined explosion. However, since scab¬ 
bing may be produced by contact explosion of high- 
capacity weapons unable to penetrate, and is a serious 
danger to personnel or equipment exposed to it, means 
of preventing or controlling scabbing are desirable in 
many situations. 3 Since the scab is shallow, it is not 
greatly affected by interior reinforcing of the slab 
unless the latter is near the inside face. If there is a 
layer of steel bars near the inner face it will generally 
cause a plane of weakness that facilitates scabbing. 
If the reinforcing layer is moved nearer the face of 
the slab the amount of scabbed material decreases. For 
a layer of steel bars, or a steel mesh, against the slab 
face, a scab may form but will not leave the slab 
provided the bars or mesh are firmly tied to the in¬ 
terior reinforcing. An alternative is to use a scab plate 
which must also be tied in to the interior reinforcing. 
No information on the design requirements of such 
antiscabbing devices is available. See also Section 


7.2.3 of Chapter 7. Another scheme, much used by the 
Germans in the roofs of pillboxes and covered gun 
emplacements, is to place small steel I-beams either 
side by side, or separated and with curved steel soffit 
plates between lower flanges, on the bottom faces. 
These serve three purposes, as antiscabbing protection, 
formwork during the placing of concrete, and en¬ 
hancement of resistance to perforation by bombs or 
projectiles. A double wall of concrete with air or some 
packing material between the sections also offers more 
resistance to scabbing than does a single wall with the 
same amount of concrete. The resistance to projectile 
perforation is also slightly increased. This scheme has 
two principal objections: first, detonation of an HE 
shell in the inner space will be much more destructive 
because of the confinement than if it detonated at the 
bottom of its normal crater in a solid wall; second, 
the cost of construction is increased by the complica¬ 
tions of a double wall. 

Cratering 

A crater is produced at a point of impact or im¬ 
pulse, or by an internal explosion. Craters in earth are 
discussed in Chapter 3, craters in concrete from pro¬ 
jectile impact in Chapter 7. Craters are also produced 
in concrete by contact or near-contact explosions; 
these are the subject of this section. 3 ' 6 

Presumably, a crater is produced b} r an explosion 
as the result of very high, verv concentrated forces 
underneath the explosion. These force material in¬ 
ward, causing breakup and displacement of a cone of 
material surrounding the inward moving region. No 
complete investigation of the mechanism of cratering 
has been made. The normal shape of a crater produced 
by contact explosion is quite different from that of a 
scab. The shape is nearly but not exactly conical. The 
depth is approximately 0.5 and the diameter 2.5 times 
the cube root of the volume (expressed in the same 
units). 

Since the crater is caused by the explosive pressures 
its size will be affected by anything that affects the 
magnitude, the duration, or the distribution of explo¬ 
sive pressures. For contact charges of a constant 
amount of a given explosive, a change of shape of the 
charge has considerable effect on its cratering ability. 
A change of shape also affects the impulse produced 
by a given amount of explosive, as will be discussed 
later. Thus it is logical to assume that some relation 
exists between the impulse and the cratering power of 
a given charge. However, it is clear that other factors 
will also affect the situation, since the impulse exerted 


• ;• i>! yn a' 






EXPERIMENT 


287 


by an explosion is the time integral of the total force 
exerted on the whole surface of the slab, whereas the 
crater is caused by the very large pressures in the 
immediate vicinity of the charge and only so long as 
they exceed the confined compressive strength of the 
material. An extensive series of tests 4 has shown that 
good correlation exists between impulse and crater 
volume, but the rather serious scattering of data 
indicates that other factors are important. This rela¬ 
tion is approximately 

V = 1.5 J, (4) 

for charges on end and detonated at the end away 
from the slab, and 

V = 1.2 J, (5) 

for charges lying on their sides and detonated at one 
end. V is the crater volume in cu in. and J is the 
total impulse of the explosion in lb-sec, discussed later. 
The concrete is assumed to be of normal strength, of 
the order of 4,000 psi. 

The crater volume is affected by a number of factors 
whose influence is not perfectly understood. For ex¬ 
ample, the volume is dependent on the concrete 
strength; preliminary tests indicate that it varies 
approximately inversely as the square root of the 
strength. 3 Thus, increasing the strength by 50 per 
cent will decrease the crater volume by about 25 
per cent. 

The orientation of the charge is very important in¬ 
asmuch as it affects the impulse very strongly, as 
shown later. Thus side-on detonation of demolition 
blocks gives volumes about 25 per cent larger than 
does end-on detonation. 

The point of detonation of the charge appears to be 
very important, and is believed to be responsible for 
much of the lack of correlation in the series of tests 
on which equations (4) and (5) are based. Prelim¬ 
inary tests 0 on concrete and steel plates using demoli¬ 
tion blocks on end and detonated either at the top 
or at the bottom gave the following results: impulses 
were affected only slightly; initiation at the bottom 
gave impulses 4 per cent greater than at the top. How¬ 
ever, initiation at the top gave greater damage; in 
mild steel, crater volumes were doubled, and in con¬ 
crete they were nearly quadrupled over those for base 
initiation. 

Some tests 4 made with different explosives indicate 
that there is close correlation between crater volume 
and both velocity of detonation in the explosive and 
the so-called “plate denting index” used by explosive 
technicians as a measure of the brisance of an explo¬ 


sive. As detonation velocity increases from 22,500 fps 
(TNT) to 25,500 fps (Comp. B), the crater volume 
for a given weight and shape of charge increases by 
about 60 per cent. These are onl} T tentative relations, 
however. 

15.2.4 Impulse Delivered to a Slab 
by a Contact Explosion 

When a charge detonates near a flat surface, pres¬ 
sures are exerted on the surface that may cause it to 
move or may damage it. For contact charges the same 
effects occur. In this case the damage may be charac¬ 
terized either as local or as indirect. The first depends 
very much on the intensities of pressure acting, as 
well as on the durations. Indirect damage can occur 
in portions of the target structure that are distant 
from the charge; it depends mostly on the impulse, 
or total integral with respect to time of the force act¬ 
ing on the structure. 

The direct measurement of pressures from contact 
charges is extremely difficult because of the intensities 
that occur. It may be possible by indirect methods 
to obtain some idea of intensities, i.e., from compar¬ 
ison of crater dimensions in materials of different 
strengths. Impulse, however, can be measured quite 
easily. Such measurements are useful in dealing with 
the indirect damage resulting from contact explosions, 
and are also related to the local damage, such as 
cratering, since some of the factors altering pressures 
must also affect impulse. However, as shown in the 
discussion of the relation between impulse and crater 
volume given in the previous section, the extent of 
local damage can be greatly changed by such things 
as changing the point of initiation, which results in 
only secondary changes in impulse. 

The impulse from a contact explosion is the time 
integral of the total force exerted on the target. This 
must include both the very intense instantaneous 
pressures under the charge and the longer lasting 
pressures surrounding the charge following the ex¬ 
plosion. The impulse will certainly depend on the kind 
of explosive and on the shape of the charge used. 
Thus a long, thin stick of explosive perpendicular to 
a surface will deliver a smaller impulse than the same 
stick lying flat, or the same amount of explosive in a 
short, wide cylinder. In other words, to increase im¬ 
pulse by adding explosive, it should be added in con¬ 
tact or near contact for the greatest effect. The im¬ 
pulse is affected by confinement. Thus a given amount 
of charge in a crater is confined on the sides and must 
expand more in a vertical direction than if it were on 


C ONFT DE NTI AHj 







288 


STRUCTURAL PROTECTION 


a plane surface. 9 This effect may result in an apparent 
difference in behavior between strong materials and 
weak materials, since the formation of a crater may 
be an essentially unstable process which proceeds more 
rapidly with an increase in size. 

The Impulse Pendulum 

For measuring explosive impulses an impulse pen¬ 
dulum 7,8 was constructed at Princeton. This is essen¬ 
tially a steel frame about 12 ft high from which is 
pivoted a steel member supporting two pieces of armor 
plate which are placed back to back and separated by 
the thickness of the pivoted supporting member. An 
impulse normal to the surface of one piece of plate 
will cause the plates and their support to swing about 
the pivot. The amount of swing can be measured and 
used to calculate the impulse. Different sizes of plate 
can be used; the largest were 2 ft square and 3 in. 
thick, weighing approximately 1,200 lb (two plates). 
Charges can be detonated at the center of one plate 
and their impulses measured. 

For the charge sizes (up to 2.3 lb) and plate sizes 
(18 to 24 in. square) that have been used there 
appears to be no effect of plate size. Thus, for a plane 
surface, the impulse delivered is found to be dependent 
on the weight of charge, the type of explosive, and a 
geometrical shape factor. Dimensional considerations 
indicate that if other things are kept constant the 
total impulse is directly proportional to charge 
weight. 9 The relative effectiveness of different explo¬ 
sives can be represented by explosive coefficients; 
several of these are shown in Table l. 4 


Table 1 . Relative explosive factors for impulse. 


Explosive 

Factor 

TNT 

1.00 

Tritonal 80/20 

1.03 

Tetrytol 50/50 

1.04 

Comp. B 

1.07 

Pentolite 50/50 

1.07 

C-3 Plastic explosive 

1.14 

HBX-2 

1.22 

Tetryl 

1.58 


Tests have been made for a large variety of charge 
shapes. From these it appears that the geometrical 
parameter can be taken as h/yffA, where li is the 
dimension of the charge perpendicular to the target 
surface and A is the sectional area of charge parallel 
to the surface. For a cylindrical charge with its axis 
parallel to the surface, A can be taken as its plan area 
(diameter times length). Thus impulse can be ex¬ 
pressed as the product of charge-weight times the 


explosive factor given in Table 1, multiplied by a 
function of the shape factor /t/y A. For TNT (either 
pressed or cast) the following relation for impulse 
has been determined: 


W x 0.87/t ’ v A 

where J is the impulse expressed in lb-sec. This is 
based on experiments in which h/\/A ranged from 
0.25 to 5.4. 

An important result of this investigation is the 
knowledge that considerable differences in impulse 
can be obtained with a given charge simply by chang¬ 
ing its orientation. For example, a TNT demolition 
block weighs V 2 lb and is 1.75 in. square by 3.25 in. 
long. On end, its shape factor is 1.86; on one side 
it is 0.74. From equation (6) the corresponding im¬ 
pulse factors are 70 and 110. Thus end -011 and side -011 
impulses from a block are 35 and 55 lb-sec. 

The effect of changing the point of initiation of the 
charge was investigated. 6 The effect on impulse was 
found to be very small, amounting to only 4 per cent 
in the case of demolition blocks on end. Base initiation 
gave the greater impulse. The effect of small standoff 
was not studied. It is probable that the effect of stand¬ 
off on impulse is much less than the effect on local 
damage discussed in a previous section. 

15 2 5 Impact Tests of Reinforced Concrete 

Beams 

At the University of Illinois an extensive test pro¬ 
gram was conducted 011 the behavior of small rein- 
forced-concrete beams under impact. 10 ' 12 The tests 
were arranged in seven series, each series designed to 
determine the effect of varying some beam parameter. 
In all, 435 beams were tested. Impact was produced 
by hammers, weighing from 7 to 50 lb, striking the 
beams centrally at velocities up to about 100 fps. The 
hammers were accelerated by compressed air driving 
a piston. 

The following sets of tests were made: 

Series 1. Effect of type of contact between hammer 
and beam. Interposed bearing plates of three sizes 
and weights were employed to transmit the impact to 
the beams. A few tests were made without bearing 
plates. 

Series 2. Effect of amount and grade of longitudi¬ 
nal reinforcing steel with light web reinforcement. 
One group of beams had no web reinforcing. 





















EXPERIMENT 


289 


Series 3. Effect of amount and grade of longitudi¬ 
nal reinforcing steel with heavy web reinforcement. 

Series 4. Effect of type of web reinforcement, in¬ 
cluding ordinary U-stirrups, spirals, and welded units. 

Series 5. Effect of concrete strength, with stirrups. 

Series 6. Effect of artificial scabbing planes, beams 
with and without stirrups. 


Series 7. Effect of varying beam spans. 

The beams of series 1 to 5 were 4 in. wide, 5*4 in. 
deep, and 47 in. long on 42-in. span with the impact 
applied at midspan. A detail of a typical beam is given 
in Figure 1. The beams of series 6 were identical to 
these except for the addition of 2 V 2 in. of concrete and 
two %-in. bars added to the bottom. The beams of 



B C 


Figure 1 . Typical details of test beams. A. Elevation. B. Cross section. C. Detail of hook at end of bar. 


CONFIDENTIAL 




























































































































290 


STRUCTURAL PROTECTION 


series 7 were of identical section to that shown in 
Figure 1. They varied in length by 2-ft increments 
from 30-in. to 126-in. and provided spans of 2, 4, 6, 
8, and 10 ft. Except for series 5 all beams were 
made of concrete of the same mix, intended to give a 
compressive strength of 4,000 psi. The concrete was 
cured moist for 7 days, then stored until the beams 
were tested at the age of about 28 days. Generally, 
twelve beams of a kind were poured at the same time 
to provide for impact tests with three hammer 
weights, each at four velocities. Two 4x8-in. control 
cylinders were made with each batch of three beams 
and were stored with them and tested at the same time. 

Testing Procedure 

The beams were tested in the pneumatic impact¬ 
testing machine that is illustrated in Figure 2. The 
ends of the beam were supported on short lengths of 
12-in. steel I-beam transverse to the length of the test 
beam, and were clamped in such a way that the ends 
of the test beam were held down during the test but 
were not restrained against rotation. 

In all the tests except those of series 1 the impacts 
were applied through a 4x3xM>-in. steel bearing plate 
embedded in a thin layer of plaster of Paris at the 
midspan of the beam. 

The natural frequency of each beam was measured 
both before and after impact in order to secure a sim¬ 
ple, quantitative measure of the extent of damage pro¬ 
duced by impact. 

The velocity of the hammer was measured just be¬ 
fore impact. In order to limit the stroke of the ham¬ 
mer and to prevent it leaving the pneumatic cylinder, 
a stop was placed beneath the test beam which limited 
the deflection of the beam under the heavier impacts. 
Because the air pressure in the piston was not released 
during impact and was reduced by only about 6 per 
cent because of the increase in volume as the hammer 
was driven downward, a continued static force was ex¬ 
erted on the hammer, and consequently on the beam, 
after impact. Not only did this static force resist re¬ 
covery of the beam after impact, but it contributed to 
the deflection, increasing it beyond the amount that 
would have occurred under impact of the hammer at 
the same velocity but without air backing. This effect 
is discussed further in Section 15.5.1. 

After impact, the permanent deflection was record¬ 
ed, and a sketch made of the beam showing the extent 
of spalling or scabbing and the pattern of cracks. Pho¬ 
tographs were taken of all beams to record the visible 
damage. After the second determination of natural 


frequency, the beam was loaded statically to failure to 
determine by what amount the load-carrying capacity 
had been diminished by the impact. 

Conclusions 

Effect of Weight of Bearing Plate. Three weights of 
bearing plate, 0.04, 1.7, and 19 lb, were used. With the 
7.5 and 18-lb hammers the greatest damage was pro¬ 
duced with the 1.7-lb plate; with the 50-lb hammer 
the greatest damage occurred with heavy plate; but 
with all three hammers, the tendency to scabbing was 
greatest with the light plate. 

As would be expected, the permanent deflection of 
the beam decreased with an increase in the weight of 
bearing plate, and the greatest change occurred with 
the lightest hammer. With the 50-lb hammer the effect 
of the bearing-plate weight was very small. 

Effect of Repeated Impact. Several beams of series 
1 were subjected to a repetition of impact. Even after 
a light impact, the second blow increased the deflec¬ 
tion as would be expected, since each blow adds rough¬ 
ly the same amount of energy to the beam; if one blow 
causes plastic deformation the second may be expected 
to cause additional deformation. A rapid increase in 
structural damage seems likely with repeated impacts. 

Effect of Variations in Amount of Reinforcing 
Steel. The role of longitudinal reinforcing is to resist 
bending of the beam as a whole, whereas the web rein¬ 
forcement serves to maintain the integrity of the 
beam. Under concentrated impact, as in the present 
series of tests, there is a strong tendency for the beam 
to be broken up in the vicinity of the blow. Such 
breaking up can completely destroy the bending 
strength of a beam by removing the concrete surround¬ 
ing the tensile bars at the section of the greatest bend¬ 
ing moment. Consequently, for impacts of this kind, 
web reinforcing is very important in order to confine 
the concrete after it cracks; it also tends to prevent 
buckling of longitudinal steel when vibration of the 
beam puts it into compression. Various arrangements 
of web reinforcing were tried. There appeared to be 
little difference between these provided they were capa¬ 
ble of the two functions just mentioned, restraint of 
concrete after cracking, and restraint of longitudinal 
steel against buckling. It should be mentioned that 
since a beam will vibrate upward as well as down, both 
top and bottom bars go into compression. It should also 
be pointed out that beams or panels subjected to dis¬ 
tributed impulsive loads are very much less liable to 
local breakup, and the principal function of any web 


Confidential | 






EXPERIMENT 


291 



Figure 2. Pneumatic testing machine with beam in 
place for test with 50-lb. hammer 


reinforcing is then to prevent buckling of longitudi¬ 
nal steel. 

The heavy hammers tended to produce vertical 
cracks (similar to those occurring during static load¬ 
ing tests), whereas the lighter hammers tended to 
cause the diagonal cracks characteristic of scabbing. 
The velocity of impact appears to be the most impor¬ 
tant factor in scabbing; the lightest hammer at the 
highest velocities caused extensive scabbing and spall¬ 
ing. 

There is some indication that an increase in the 
hammer velocity tends to cause a decrease in the in¬ 
itial slope, yield load, and maximum load obtained in 
the static test following impact. This effect would be 
expected since the higher velocity impacts would tend to 
produce more extensive cracking throughout the beam. 

Effect of Concrete Strength. The compressive 
strength of the concrete had only a secondary influ¬ 
ence on the action of the beams except for the impacts 
of greatest energy, for which the intermediate- 
strength concrete appeared to offer the greatest resist¬ 
ance. With low-strength concrete, the principal phe¬ 
nomenon accompanying failure appeared to be crush¬ 
ing of the concrete immediately under the bearing 
block. With the high-strength concrete, there was a 
wedging and splitting action beneath the bearing 


block, a chunk of concrete being forced down into the 
beam, spreading the stirrups and longitudinal steel 
apart. This action would have been much less serious 
if the stirrups had been complete loops instead of U- 
shaped, as in this particular test. 

In general, it may be said that the concrete serves 
four functions: (1) it furnishes mass (the greater the 
mass of the beam, the less energy is given to it, other 
things being equal), (2) it furnishes compressive 
strength to balance the tension of the stretched longi¬ 
tudinal bars, (3) it keeps this tension at a distance 
from the compression portion of the beam, which is 
necessary for bending strength, and (4) it is the me¬ 
dium for transferring the impulsive load to the beam. 
For amounts of longitudinal steel such as used here 
(about 1.5 per cent at the bottom of the beam), the 
steel yields more than the concrete, even for concrete 
of moderate strength. (Note that a beam may be over¬ 
reinforced for elastic deformation and at the same 
time underreinforced for plastic.) Thus, changing the 
concrete had little effect on the bending strength of 
the member, but would be expected to affect the local 
failure occurring under the load. 

Effect of Artificial Scabbing Planes. Horizontal 
planes of weakness were introduced near the bottoms 
of beams with the thought that under impact, separa¬ 
tion would occur at this section and that the scabbed 
material would carry away from the beam most of the 
energy given it, avoiding further damage to the beam. 
Unfortunately, practically no scabbing was caused in 
any of the experiments and it is impossible to draw 
any conclusions as to the possible efficacy of this 
scheme. These beams were, however, decidedly unsat¬ 
isfactory since they were considerably weaker statically 
than beams of the same total depth without scabbing 
planes. 

Effect of Span Length. These tests furnished only 
a partial answer to the question as to the effect of span 
on the impact resistance of a beam, since the results 
were complicated by the effect of the continuously act¬ 
ing air pressure in the cylinder of the hammer. The 
force so applied was, for the higher pressures and 
longer beams, of the same order as the static strength 
of the beams, hence the additional deflection due to 
this alone was too great to neglect. However, some of 
these results have been analyzed by the theory of plas¬ 
tic action discussed later in this chapter and illustrat¬ 
ed in Section 15.5.1. Since this analysis gives results 
that agree generally with the observations it is con¬ 
cluded that the analysis is reliable. According to this 
theory the general or distributed damage (plastic 


CONFIDENTllf 
















292 


STRUCTURAL PROTECTION 


bending) decreases with an increase in span. This con¬ 
clusion is partly supported by the results of these tests, 
since it was found that at low impact velocities, cor¬ 
responding to low air pressures, resistance of beams 
increased with span. However, local damage is nearly 
independent of span. 

The deflected shapes of the beams were determined 
after impact and found to be approximately linear 
from the span center to each support, with a short 
curved portion in the vicinity of the span center. 
There was also a small negative curvature in the outer 
portions near the supports. 

Reference should be made to Sections 15.3.2 and 
15.5.1, which discuss the analysis of these tests. 

153 THEORY AND ANALYSIS 

Because of the great variety of structures, materials, 
attacking agents, and conditions of attack, no experi¬ 
mental study can be complete. Thus, it is desirable to 
develop a method of analyzing structural behavior, in 
order that the results of the limited number of experi¬ 
ments that can be made may be used with confidence 
in predicting the behavior of structures of types that 
have not been investigated or that are subjected to 
situations that have not been studied experimentally. 
A method of analysis must fulfill certain require¬ 
ments : 

It must be simple and straightforward enough for 
use by the individuals who will have to use it, or else 
be reducible to graphs or tables for such use. It must 
give results that are reasonably reliable, possibly 
within a factor of 2, although this will depend on the 
particular situation; an empirical parameter intro¬ 
duced to make the analysis fit observation is permis¬ 
sible, but its presence limits the applicability of the 
analysis to situations similar to the ones for which 
agreement has been achieved, making extrapolation 
to other situations uncertain. An analysis must rec¬ 
ognize the conditions of the problem; if the conditions 
of ultimate failure of a plastic structure are desired, 
then even a very good elastic analysis is of limited 
usefulness until the relation between the results of the 
analysis and the ultimate plastic state of the structure 
is known. 

Elastic versus Plastic Design 

Almost without exception, structures and structural 
elements exhibit both elastic and plastic behavior. 9 
For loads below a certain load, removal of the load 
allows the structure to return to its original state; 


this is the definition of elasticity. (The relation be¬ 
tween load and deflection is usually linear, but does 
not need to be.) For loads greater than the elastic 
limit, removal of the load does not result in the struc¬ 
ture returning to its original state. The shape of the 
load-deflection relation is well known; an example 
is the stress-strain curve for structural steel. Nor¬ 
mally, by far the greatest part of the area beneath the 
curve, which represents work done on the structure, is 
under the plastic portion; for mild steel or for an 
underreinforced concrete beam the total elastic energy 
is of the order of 1 per cent of the total deformation 
energy. 

A static load is usually a specified force; occasion¬ 
ally it may be a specified deflection. A static load will 
seldom, if ever, be specified as a given amount of 
energy. A dynamic load, on the other hand, usually is 
applied either through impact by a mass having a 
given velocity, or as a force having a given variation 
with time. In each case the effect is to load the struc¬ 
ture by giving it a definite quantity of energy (which 
may depend on the characteristics of the structure). 
This is the fundamental difference between static and 
dynamic loads; the former is usually a definite force 
capable of doing any amount of work within limits, 
while the second amounts to giving the structure a 
definite amount of energy whose amount may depend 
on the structure, but which, once given, must be 
handled by the structure to the best of its ability. 

Ordinary, engineering design nearly always is based 
on the assumption of elastic behavior in the structure. 
There are several reasons for this. In the first place 
the loads are generally static and the difference be¬ 
tween the elastic-limit load of a structure and the 
greatest load it can take is not very large; the ratio 
is generally of the order of 1/2. In the second place, 
loads on ordinary structures may be removed and 
applied a large number of times. Unless stresses are 
kept well below the elastic limit, repeated loading will 
cause gradual deterioration and eventual failure. 
Finally, large deflections cannot be tolerated in most 
structures intended for everyday use, partly because 
cracking and noticeable sagging are not attractive. 

Structures intended for protection against explo¬ 
sion or impact have been analyzed both elastically and 
plastically. The British used plastic analysis in design¬ 
ing certain air-raid shelters. The resistance of a plate 
or slab to a projectile is, of course, based on its plastic 
resistance, not its elastic strength. On the other hand, 
calculations based on elastic theory have been used in 


_ 



THEORY AND ANALYSIS 


293 


the design of certain fortifications for the Corps of 
Engineers. 

A structure can be designed for ultimate conditions 
either by means of what may be termed a plastic an¬ 
alysis, which attempts to take account of the actual 
mechanism of deformation of the structure, or by 
what may be called an elastic analysis, based on the 
usual elastic theory of structural design, but in which 
the permissible stresses are chosen, on the basis of 
experience, to yield an estimate of the true ultimate 
strength. Each method has certain advantages and 
disadvantages. The plastic analysis is the more real¬ 
istic and rational. In situations where it can be ap¬ 
plied but for which actual empirical information is 
lacking it is the more reliable. Its principal disadvan¬ 
tages are that it is entirely unfamiliar to most engi¬ 
neers, that at present it has been applied specifically 
only to certain comparatively simple design problems, 
and that some intuition and experience are needed 
by anyone applying it. The elastic method of analysis, 
although not especially simple in application, is more 
familiar to engineers than is the plastic method. It 
can also be applied to practically any type of structure. 
It has the disadvantage that it can be used to predict 
ultimate conditions only by the use of hypothetical 
allowable stresses of the order of ten times the actual 
ultimate strengths of materials. These hypothetical 
stresses can be reliably obtained only by comparison of 
elastic analysis with experiment. Where experiment is 
lacking, the use of hypothetical stresses based on other 
structural situations is risky. 

To sum up: (1) A method of analysis designed to 
allow prediction of ultimate resistance is required for 
many problems of military design. (2) By the use of 
hypothetical design stresses (well above the actual ul¬ 
timate strengths), the ordinary method of analysis, 
based on elastic theory, can be used for this. This can 
be applied to more situations and can be used by de¬ 
signers of less experience than can plastic analysis. 
(3) A method of analysis, based on the actual behavior 
of structures in the plastic state, has been developed. 
This is more rational than the elastic method in that it 
does not require the use of empirical factors. 

15 31 Elastic Response of Structure 

to Impact or Impulse 

The methods of determining the elastic behavior 13 ' 15 
of a structure under dynamic loading are based on the 
assumption that the relation between force and de¬ 
flection (or stress and strain) is linear. A linear 
system is one for which force and deflection are pro¬ 


portional and for which removal of load results in a 
return to the original state. Such a system, when dis¬ 
turbed dynamically, tends to oscillate in its so-called 
natural modes or shapes of vibration. The natural 
modes of a stretched string are well known and consist 
respectively of one loop, two loops, three loops, etc., 
having progressively higher frequencies. When this 
system is disturbed and allowed to oscillate, all or 
most of the modes are excited and the resulting mo¬ 
tion, although very complicated in appearance, con¬ 
sists only of combinations of these modes and fre¬ 
quencies. When a continuing disturbance is given to 
the string it acts in a definite way on each mode, and 
the response of the whole string can again be expressed 
as the sum of the responses of all its modes. Exactly 
similar considerations apply to any linear system. 
Such a system has natural modes, or shapes of vibra¬ 
tion, each with a definite frequency. There may be an 
infinite number of modes (characteristic of so-called 
continuous systems such as the stretched string or a 
beam), or a limited number of modes, as in the case 
of a weightless spring supporting a series of weights. 
In general, the number of modes is equal to the num¬ 
ber of quantities needed to describe the possible con¬ 
figurations of the system. Thus a system that consists 
of a spring supporting two masses that can only move 
vertically can be described completely by giving the 
vertical position of each mass, and has, therefore, 
two degrees of freedom and two modes. 

The general problem of finding the elastic response 
of a system to a disturbance first requires determining 
the modes and frequencies of the system. Frequently, 
only the modes of lowest frequency are needed. Next, 
the effect of the disturbance on each mode is deter¬ 
mined, and finally the total effect is found by com¬ 
bining the various mode effects. An exact mathe¬ 
matical solution is always possible but is frequently 
very difficult and tedious. There are various ways of 
simplifying the work. One is by using approximate 
shapes for the modes and determining from these 
shapes what the approximate frequencies are, then 
using these shapes and frequencies exactly as though 
they were the actual ones. This method, known as the 
Ritz-Rayleigh method, is a very useful one. It is neces¬ 
sary that the chosen mode shapes be possible ones and 
as close as possible to the real ones, and that important 
modes are not left out. Model tests facilitate mode and 
frequency determination. The reader who desires to 
apply the elastic method is referred to the references 
listed at the beginning of this section. 


CONFIDENTIAt 










STRUCTURAL PROTECTION 


294 

15 3 2 Plastic Response of Structure 
to Impact or Impulse 

An analysis of the plastic behavior 9 ’ 13 of a structure 
is concerned with predicting the effect of a load that 
is sufficient to exceed the elastic limit of the material, 
usually by a considerable amount. There are various 
possible approaches to this problem. One is based on 
a mathematically exact analysis in which every at¬ 
tempt is made to represent the physical properties of 
the material correctly, either by equations or by 
graphs. This analysis must follow the structure 
through all phases of its response, and usually be¬ 
comes extremely complicated as a result. This method 
is used in the plastic wave propagation studies dis¬ 
cussed in Chapter 12. This approach has certain ad¬ 
vantages in that strange and unexpected phenomena 
may be revealed by it that would not normally be 
discovered, such as the critical velocity of impact. The 
disadvantage is that the amount of labor involved in 
application is considerable and only very much ideal¬ 
ized problems can usually be solved. Furthermore, in 
practical cases the various damaging agents involved 
and the characteristics of the structure are not usually 
known with any exactness. For this reason, another 
approach has been found to be more satisfactory in 
handling most practical problems. 

An approximate method has been used for dealing 
with the plastic response of structures to impact or 
impulse that generally resembles the elastic method 
outlined above. First, the nature of the response of 
the structure is guessed at. This is the simplest and 
also the most critical part of the analysis. For com¬ 
plex structures it may be necessary to complete the 
analysis using several alternatives and to select the 
best one finally. The next step is either to calculate 
the amount of energy given to the structure during the 
impact or impulse and to use this to determine the 
final condition of the structure, or to set up a relation 
between the various forces known to be acting, the 
internal resistance to deformation, and the inertial 
reactions of the structure. These methods are shown 
in Sections 15.5.1 and 15.5.2 respectively. Although 
these methods are far from exact, examination of Fig¬ 
ures 3 and 4 shows that in these cases at least, reason¬ 
able agreement with observation was obtained. 

154 RECOMMENDATIONS FOR 

FUTURE WORK 

The development of civilian protection can be put 
into three categories; there is much to be done with 


respect to each. These are (1) acquiring basic informa¬ 
tion, (2) applying that information to design and con¬ 
struction, (3) making overall plans for securing pro¬ 
tection. 

1541 Fundamental Research 

The information now available on the effects of 
weapons on structures is far from negligible and has 
mostly been acquired during World War II. However, 
it is not adequate, and will certainly be made less and 
less adequate now as weapons are developed. In gen¬ 
eral, the researches that have been described in this 
chapter should be extended and made more definite 
and more complete. 

Because of the atomic bomb and the expected devel¬ 
opment of weapons of higher striking velocity and 
greater accuracy, protection by burial will probably 
become increasingly important. On this account the 
effectiveness of explosions at great depths and at great 
distances from deeply buried structures becomes im¬ 
portant, and methods of securing maximum protec¬ 
tion must be sought. Also, the effects of pressures of 
long duration on exposed structures must be deter¬ 
mined, and means of minimizing these effects dis¬ 
covered. 

15 4 2 Applications to Structures 

Development in this direction has been much less 
than that on basic problems. In the case of ordinary 
structures it is desirable to determine what changes 
in existing structures and what changes in design and 
construction practice will most increase the resistance 
against air blast and earth shock. An examination of 
structures damaged and destroyed in England and 
Germany indicates that certain kinds of structures 
are peculiarly susceptible to large-scale collapse, for 
example the thin, concrete barrel-arch roof. Multi¬ 
story structures with load-bearing brick or masonry 
walls are more vulnerable to internal or external blast 
than are frame buildings. Light beam connections may 
allow collapse that would have been prevented by 
heavy connections. Such considerations as these indi¬ 
cate that without great cost it may be possible to in¬ 
crease the blast resistance of cities by significant 
amounts. The economic advantages or disadvantages 
of such a plan should be investigated. In any event, 
it is very desirable that the relative safety of struc¬ 
tures be determined in order that the more important 
facilities may not be left in the more dangerous 
places. 


,'o;ni iiv,- 









APPENDIX 


295 


15 4.3 Overall Organization of Protection 

Since most parts of this country will be vulnerable 
to attack in any future war it is of very great im¬ 
portance that protection for possible targets be 
planned. Since such protection will require extensive 
planning and a very long time to complete, it seems 
desirable to begin the task immediately. Such a plan 
will involve a great many things that have no connec¬ 
tion with the present discussion. However, the follow¬ 
ing must be considered: (1) the various aspects of 
protection must be decided on, i.e., surface shelters, 
buried structures, methods of strengthening or pro¬ 
tecting existing buildings, changes in building codes 
for bettering future construction; (2) the various 
standards of design and construction needed for the 
items enumerated above, i.e., methods of analysis, de¬ 
sign loads, design stresses. 

155 APPENDIX 


W = weight of striking body, 
w = total weight of beam, 

R — central force to overcome plastic resistance of 
beam (assumed constant), 

V 0 = striking velocity of weight, 
v 0 = common velocity of weight and beam at time 
T, 

v = velocity of beam at point of impact at any 
time, 

x = maximum permanent center deflection, 

E 0 = V 2 W/gV 2 o — (initial energy of TF), 

E — total impact energy available for bending 
beam (the difference between E 0 and E is 
used up in producing local damage at the 
point of impact), 

P = average force due to pressure on piston (tests 
of Section 15.2.4), 

E b — E plus work done by P during deflection. 

During the first stage of the impact the impulse act¬ 
ing on IF must equal its loss of momentum: therefore, 


15.5.1 Plastic Analysis of Reinforced 
Concrete Beams under Impact 

Uniform, Simply Supported Beam Struck at 
Center by Weight W 

Following the contact of the weight and beam the 
former is decelerated and the latter speeded up until 
they move together. Ordinarily, this will occur very 
quickly, in a time short compared to the total time 
required for the beam to come to rest again. Conse¬ 
quently, the reactions of the supports will be small 
compared to the force acting between the beam and 
weight. The shape of the beam is assumed to be para¬ 
bolic or sinusoidal throughout the whole process, in¬ 
cluding both the period of acceleration under impact 
and the subsequent period of deceleration due to the 
plastic resistance of the beam to bending. 

If the beam deflects sinusoidally its average deflec¬ 
tion at any instant, taken over the whole span, is ap¬ 
proximately % its maximum deflection at the instant. 
Similarly, its average velocity and average accelera¬ 
tion are, respectively, % the velocity and acceleration 
at the center. Furthermore, the average of the square 
of the velocity over the whole span is V 2 the square of 
the center velocity. 

The following symbols are defined: 

F = the force between beam and weight at any 
instant, 

t — time (variable), 

T = duration of impact, 



r IF 

Fdt=j(V 0 -v 0 ). 



The work done by F on the beam up to any instant t 
must be approximately equal to the kinetic energy ac¬ 
quired by the beam at that time; therefore, 


1 wv l 

Fvdt = 


4, 9 



This expression can be differentiated, yielding F == 
(w/2g) ( dv/dt) which is substituted in equation (7). 


Since 



dv _ 
— dt — v 
dt 


0 > 


this gives 


^0 


F 0 

l+IL 

21 F 



Finally, the total energy given to the system consist¬ 
ing of the beam and weight is 


E = 


Er 


1 + 


w 

2TF 


( 10 ) 


The energy given by equation (10) is available for 
bending the beam. Although the shape of the beam 
under dynamic bending will differ somewhat from the 
static shape the difference can be ignored in this ap¬ 
proximate analysis. The relation between force and de¬ 
flection of a beam can be determined by calculation 
with sufficient accuracy for present purposes; however, 







296 


STRUCTURAL PROTECTION 


there are usually available results of loading tests that 
cover the plastic range. From these the relation be¬ 
tween deflection and external work can be found. 

The procedure to be followed is then: 

1. Calculate E 0 the striking energy of W, 

2. Calculate the available energy from equation 

( 10 ), 

3. From the deflection-work relation obtained stat¬ 
ically and the amount of energy available deter¬ 
mine the permanent center deflection. 

A similar process can be followed for other kinds of 
impacts or for impulses. For example, if the falling 
weight is not a single mass, but is distributed uni¬ 
formly along the length of the beam (falling debris 
would be so treated) the energy available is 

E =— (11) 

„ , w 


From a concentrated impulse J, of very short dura¬ 
tion, acting at the center of span the available energy 
is 



( 12 ) 


From a uniformly distributed impulse of very short 
duration, the available energy is 


4 J 2 

F — _ __ 
2 

7 r w 


(13) 


Analysis of Impact Tests Discussed in 
Section 15.2.5 

The relation between work and deflection in the 
plastic range for a reinforced concrete 9 beam can gen¬ 
erally be represented quite accurately by an equation 
of the form 

a-= ^ (®i, — «) > (14) 

where B is a constant equal to the average central 
force required to cause plastic bending of the beam. 
The quantity e is small, and corresponds to the fact 
that a small amount of energy can be absorbed elas¬ 
tically by the beam without causing any permanent 
deflection. E b is the total energy supplied, normally 
equal to E. 

An approximate value of B for beams that are not 
too heavily overreinforced and of normal proportions 
can be obtained in the following way if tests are 
not available. 

1. For a simple span the effective bending length 
U is less than the actual span L by approximately 
twice the depth of beam d. 


2. The average plastic yielding moment is approxi¬ 
mately % X a X A s X d, where <r, A s , and d are the 
average plastic strength of reinforcing, the total area 
of tensile steel, and the depth of beam to tensile steel, 
respectively. Then, 


3aA s d 
L — 2d ’ 


(15) 


The tests described in Section 15.2.5 can not be 
treated directly by use of equation (10) because of the 
fact that during the entire deflection time there was 
transmitted to the beam an additional force due to the 
air pressure in the cylinder acting through the ham¬ 
mer. If E is the energy available at the instant of im¬ 
pact, then by the time the system has come to rest an 
additional amount of work has been done equal to the 
average piston force P multiplied by x , the center de¬ 
flection of the beam. Consequently, the energy used up 
by the beam exceeds the initial energy supplied by W 
by the amount Px. This leads to the following approxi¬ 
mate relation between E b , the energy of deformation, 
and E, the energy available from the falling weight: 

Eb ~ ~~p’ (16) 

1_ B 

Then, for the present tests, equation (10) is replaced 
by 



This, with equation (14), permits prediction of the 
permanent deflection produced in the tests under dis¬ 
cussion. 

One series of these tests has been analyzed. The 
analysis is outlined in Table 2, and the results of the 
analysis shown in Figure 3, which allows comparison 
between observation and prediction. The results ap¬ 
pear to be adequate for engineering purposes; how¬ 
ever, the consistently too-large effective energy pre¬ 
dicted for the heavy hammer, and too-small effective 
energy for the light hammer indicate that the analysis 
can be improved. The difference is believed partly 
due to the fact that at equal effective energies the light 
hammer does more local damage than does the heavy 
hammer, on account of the higher velocity of the 
former. An additional reason is that the deformed 
shape of the beam depends somewhat on the velocity 
of impact; at the higher striking velocities of the light 
hammer the proportion of the beam participating in 
the deflection is less, hence the loss of energy is less, 
than for the heavy hammer. 












APPENDIX 


297 



EFFECTIVE ENERGY IN INCH-POUNDS 

Figure 3. Relation between observed and predicted 
permanent deflection of reinforced concrete beams. 

See Table 2. 

15.5.2 a Theory of Damage to Buried 
Structures from Underground Explosions 

Characteristics of the Structure 

The structure is assumed to be a buried or partly 
buried, hollow, reinforced-concrete box, one of whose 
faces is exposed to a nearby underground explosion. 
The inside plan dimensions of the box are L X D (L is 


the unsupported length of the front wall), while H 
is the inside height. The front-wall thickness is a , 
that of each side wall b, and of the rear wall c. The 
ratio of the cross-sectional area of the reinforcing 
steel stretched during deflection of a wall to the total 
corresponding cross-sectional area of that wall is p, 
and is not necessarily the same in all walls or in the 
two principal directions of a wall. The concrete struc¬ 
ture whose behavior will be analyzed here has no floor 
or roof; the same method can be applied to structures 
with floor and roof. The average yielding stress of the 
reinforcing steel in the plastic range is o- (inter¬ 
mediate between yield and ultimate strengths). 

Symbols 

The following symbols are defined: 

p and p c — densities of earth and concrete respec¬ 
tively, or weight per unit volume divided 
by the acceleration of gravity (unit: lb 
sec 2 per in. 4 ), 

P — pressure on face of structure at any 
time t, 

P 0 = peak pressure (unit: psi), 

I = impulse per unit area on face of structure, 
t — time, 

L — unsupported length of front target wall 
(unit: in.), 

V — effective length of front target wall for 
bending resistance ( L ' is less than L by 
an amount depending on the wall thick- 


Table 2. Analysis of impact tests of reinforced concrete beams.*/ 


w 

V 

To 

Eo 

P x 

E b 

X 

Weight of 

Maximum 

Striking velocity 

Striking energy 

Steady force 

Total energy 

Observed 

hammer 

air pressure 

of hammer 

of hammer 

after impact 

available fo • 

permanent 

(lb) 

(psi) 

(in. per sec) 

(in.-lb) 

due to 

bending beam 

deflection 





air pressure 

(in.-lb) 

(in.) 





(lb) 



50.1 

100 

238 

3,580 

490 

1,630 

0.265 

50.1 

150 

288 

5,400 

735 

3,040 

0.614 

50.1 

200 

332 

7,130 

980 

4,500 

1.081 

50.1 

300 

404 

10,300 

1,470 

8,500 

2.532 

18.1 

100 

384 

3,450 

490 

868 

0.028 

18.1 

200 

537 

6,780 

980 

2,110 

0.417 

18.1 

250 

597 

8.300 

1,225 

2,920 

0.803 

18.1 

300 

658 

10,150 

1,470 

4,140 

1.355 

18.1 

350 

708 

11,700 

1,720 

5,650 

1.754 

7.4 

100 

592 

3,380 

490 

405 

0.023 

7.4 

200 

838 

6,700 

980 

980 

0.138 

7.4 

300 

1,025 

10,000 

1,470 

1,980 

0.590 

7.4 

400 

1,180 

13,400 

1,960 

3,770 

1.151 


* Data from Table 5 of Reference 12. 

t Beams 4x5!4-in. on 72-in. span. Tensile reinforcing is 214-in. round bars at depth of 3Zs in. (I'igure 1). 
Yield point and ultimate strength of steel are 51,000 and 77,000 psi. 

R (plastic resistance of beam) = 3,050 lb from static tests or 2,900 lb from equation (14). 
t After impact, air pressure is approximately 94 per cent of initial pressure and acts on area of 5.21 in. 2 





































































298 


STRUCTURAL PROTECTION 


ness, here the difference is taken as (%)a, 
where a is front-wall thickness), 

M — plastic bending moment of a strip of 
front face of unit width, approximately 
equal to % a pa 2 (unit: in.-lb per in.), 
M f — plastic bending moment of a strip of rear 
wall of unit width, 

R = reaction on each side wall from a strip 
of front wall of unit width, during defor¬ 
mation (unit: lb per in.), 

R' = reaction on each side wall from a strip 
of rear wall of unit width, during de¬ 
formation, 

m = mass of unit area of front wall = ap c , 
m x — mass, per unit area of front face, of the 
remainder of the structure, 
m[ = mass, per unit area of front face, of the 
remainder of the structure with the ex¬ 
ception of the rear face, 
x — center deflection of the front wall at any 
time t (unit: in.), 

x m — permanent center deflection of front wall, 
y — displacement of remainder of structure 
at any time t (unit: in.), 
z = distance along a front-face strip mea¬ 
sured from a side wall (unit: in.), 

C — sum of crack widths in convex side of 
deformed wall (unit: in.), 
k — soil constant, defined in Chapter 3 (unit: 
psi), 

W = weight of charge (unit: lb), 
r = distance of charge from front face (unit: 
ft), 

A = r/WK 

A consistent system of units must be used. Here, all 
quantities will be in pounds, seconds, inches, except 
r, distance from charge to target, which must be in 
feet in order to fit the empirical equations for de¬ 
pendence of pressure and impulse on charge distance 
that are discussed in Chapter 3 and will be used. 

The Explosion 


A charge weighing W lb explodes at a distance r ft 
from the front face of the target and at about the 
depth of the center of the face. The pressure acting on 
the front face is assumed to decrease linearly with 
time from its initial peak value, so that 


P(t) = P 0 



(18) 


for t less than 2//P 0 , while P is zero thereafter. For 


explosives equivalent to TNT, P 0 and 1 at the center 
of the target face are given by the expressions below, 
which are discussed more fully in Chapter 3, 

?o=fb (19) 

and 

1 = -^575 - ( 2 °) 

9 

For near explosions P 0 and I over the greatest part 
of the front face will be less than at the center of the 
face. Consequently, in using equations (19) and (20) 
for calculating damage, a 25 per cent reduction will 
be made to allow for this. This reduction will be too 
great for distant charges and probably too small for 
near charges. 

Physical Behavior of Structure 

The pressure acting on the front wall of the struc¬ 
ture deforms it plastically, and is in equilibrium with 
its inertial resistance, its plastic resistance, and the 
reaction of the remainder of the structure. In other 
words, the work done to the front face of the structure 
by the pressure must be equal to the kinetic energy 
given the wall, plus the energy absorbed in plastic 
bending, plus the work done by the wall in moving 
the rest of the structure. Similarly, the reaction of the 
front Avail on the rest of the structure plus the pres¬ 
sures applied directly to the rest of the structure are 
in equilibrium with the inertial and other forces op¬ 
posing the motion of the rest of the structure. There 
are tAvo possibilities here; either the entire remainder 
of the structure moves as a solid, pushing back the 
earth behind it, or the rear face is deformed plastically 
by the pressure of the earth behind it, against AAdiich 
it is pushed. Normally, both possibilities must be con¬ 
sidered. The one most likely to occur is that which 
causes less damage to the front wall. 

Case 1—No Rear Wall Damage. Consider a strip of 
the front Avail of unit width, and extending from one 
side Avail to the other. Under the impulsUe pressure 
this strip will bend, assuming an approximately sinu¬ 
soidal shape; in addition, the side Avails to which the 
strip is attached will move in the direction of the pres¬ 
sure. y -f- x sin ttz/1 is the displacement of any point 
2 of this strip. Its velocity and acceleration are. 
respectively, dy/dt -j- d.r/dt sin 7 tz/L and d 2 y/dt 2 -f- 

d 2 x/dt 2 sin TTZ/Ij. 

During an infinitesimal interval of time dt, the 
external pressure acting on the entire strip does an 
amount of work. 









APPENDIX 


299 


A E = dt 



du , dx . 

dt + dt 8111 



Pdx 


A E = LP 



dt. 


( 21 ) 


During an infinitesimal interval of time dt, the 
energy expended in bending the strip plastically is 
equal to the plastic bending moment multiplied by the 
total change of curvature (provided there is no re¬ 
versal of curvature), 


„ d ,, tt 2 

AE * = dt Mx L* 


sin ~dzdt. 


A E = ' 2 ^~ dt. 
L dt 


( 22 ) 


The total kinetic energy of the strip at t is 



and the increase in this quantity during an interval 
dt is 



mL 

~2~ 


9 dy_ (dry , S_ 

4 dt [dt 2 + 7r 




<py ■ , dH 
dt 2 " T dt 2 


dt, 



The sum of the two end reactions of the strip is 



In an interval of time dt, these reactions do work on 
the rest of the structure equal to 2E multiplied by the 
distance moved in that time, 


* tt dy T ( „ d 2 y 2 m d 2 x 

* Er= dt L \ p - m dt 2 ~^rdt 2 


dt. (25) 


Equating the work done on the front wall to the 
sum of the plastic work, the increase in kinetic energy, 
and the work done on the rest of the structure, yields 


m 


ydt 2 ^ 4 ~dt 2 ) 


= P — 


7 r 2 l\I 
L 2 


(26) 


The left side of equation (26), the equation of mo¬ 
tion of the front wall, is the average inertial force 


per unit area of the wall. The first term on the right 
is the pressure, or applied force per unit area. The 
second term is the average force per unit area required 
to overcome the plastic bending resistance of the strip, 
and corresponds to the force that is transmitted to 
the remainder of the structure by the ends of the 
strip. 

The plastic-bending resistance of a beam is some¬ 
what greater than is calculated on the basis of the 
actual span. For example, in Section 15.5.1 the effec¬ 
tive span was taken as the actual span less twice the 
thickness. In the present case the thickness is rather 
large compared to the span, and the effective span 
will be assumed to be less than the actual span by 
3 /4 the thickness. Hence, in equation (26) L will be 
replaced by L ', assumed equal to L — % a, and 



d 2 x 

dt 2 


= P 


7 T 2 M 


L 


f 2 


(26') 


If the back wall of the structure is not deformed 
the resistance of the earth behind it must be consid¬ 
ered. This consists of two parts, a passive pressure, 
and an apparent mass that can simply be added to 
the mass of the structure. The first is taken as the 
average hydrostatic force due to a fluid of density 50 
per cent greater than that of earth. The apparent mass 
is taken as a mass of earth in contact with the rear 
wall and of depth (perpendicular to the wall) Vk its 
height. Neither contribution is large in the case of 
the structures considered. Then the equation of motion 
of the rear portion of the structure is 


3 p qH d 2 y 

2R + 2bP = P J— (L + 25) + m x L . (27) 


From equations (24), (26'), and 27), one obtains 



Equation (18) can be combined with equation (28) 


CONFIDENTIAL 































300 


STRUCTURAL PROTECTION 


and integrated to give 
d 2 x 


m 


m 


dt 2 

dx 

dt 


- A p B AP£ 
— A1 o — -o — 21 ’ 


(AP 0 — B)t 




mx = (AP 0 — B) - - 


AP\t 2 
4/ ’ 

APR 3 


12 / 


A maximum in a; occurs when 



(31) 

(32) 



which is normally later than the time t — 21 /P 0 , 
at which P becomes zero, and the equation (18) ceases 
to hold. In this case it is necessary to solve equation 
(28) with P equal to zero, making this solution con¬ 
tinuous with equations (31) and (32) at the time 
t = 2//P 0 . When this is done the maximum value 
of x is given hy 


A 2 1 2 / 4B \ 

2Bm y 3 P 0 A J 


(33) 


Case 2—Rear Wall Yields Plastically. The equation 
of motion of the front wall is the same as before, 
namely, 


m 


d 2 y t r d 2 x 

-f-r 


dt 


4 dC 


= P — 


7 T 2 M 

U 2 


(26') 


The two side walls are assumed to be displaced an 
amount y against the resistance due to the bending 
of the rear wall. Their equation of motion is 

2R + 2bP = m[L -f 2R 1 . (34) 

czz 


From equations (24), (26'), and (34) one obtains 
by the same process as before 


A' 2 / 2 / 45' \ 

2Em y 1 _ 3 P 0 A') ’ 


A' 


1.875 f ^ 

m L 


m 


m 


1+0.19 


(35) 


(36) 



r m 


v 4 R, 1 

0.636 

19.78 

1j 

(> + ~m , 

1 L 


m ' 




1 

m 

+ 0.19 



(37) 


Front-Face Crack Width 

When a slab is bent there is a surface within it that 
does not stretch, called the neutral surface. This is 


close to the concave side of the slab. Since concrete 
is brittle, bending causes cracks to open on the convex 
side of a slab. At any spot the average total crack 
width per unit length of slab surface will be approxi¬ 
mately equal to the distance from the neutral surface, 
which is about + the slab thickness, multiplied by 
the curvature of the slab in the direction in which 
the crack width is measured. If x m is the center de¬ 
flection, L the length of span, 3a/4 the depth of the 
neutral surface, and C the total amount of stretch 
or the crack width in the distance L , then 


C = 



(38) 


Illustration 

Consider the buried concrete structures whose tests 
are reported in Chapter 3, and the results shown in 
Figures 13 and 14 of that chapter. These structures 
are at scales varying up to 25x25 ft in outside plan 
dimensions and 17.5 ft high. The front, side, and 
rear walls are respectively 5, 2.1, and 3.33 ft thick. 
The value of p (proportional steel area) is ap¬ 
proximately 0.0014 for each wall. These structures 
were damaged by 1,000-lb TNT charges at various 
distances in earth. The value of k (soil constant) 
for the area in which these tests were made is 5,000 
psi. Then, 

IT* = 10, 

a, b, and c are respectively 60, 25, and 40 in., 

L = 250 in. and U = 205 in., 

m — 60 p c , 

m 1 = 140 p c and mjm — 2.33, 

m[ — 60 P c and m /m = 1.0, 

2b/L — 0.2, 

M = ( 3 /4) <jpa 2 = 270,000, if * = 70,000 psi, 
M/L' 2 = 6.4 psi, 

RJL — 3 (j pc 2 /L' 2 = 10.6 psi (this is found 
from the plastic bending moment in the 
back wall, which is approximately (%) 
<rpc 2 , and the relation between the 
maximum bending moment and the uni¬ 
form load 2R 1 /L per unit length, on a 
beam of effective span L '; thus 

(2R 1 /L) (L' 2 / 8) equals ( 3 /±) {ape 2 ), 
pgh = 11.8 psi, 


A 

B 


1.275X2.13 


1.08. 


2.52 

0.636(19.78X6.4X3.33 


11.8X1.8) 


2.52 


100 psi, 


< OXFIDKXTIAI* 


































APPENDIX 


301 


A' 

B f 


1.275(0.8) 


0 . 86 , 


1.19 

0.636(19.78X6.4X2 — 42.4) 
1.19 


= 113 psi, 


For Case 1 (nondeforming rear wall), 


3 ’ m, 

Wi 



For Case 2 (rear wall bends plastically) 


■2 m _ 1 

m*~ 22X 5 



(39) 


(40) 


It can be seen that Case 2 is the more likely. Equa¬ 
tion (40) is plotted in Figure 4 together with the ex¬ 
perimental points from the tests of these structures. 
It can be seen that the analysis predicts too little dam¬ 
age at large distances and too much damage at near 
distances. The reason for this is not clear, but may be 
associated with the fact that the nearer the charge to 
the target the less uniform the loading becomes, while 
for distant explosions the loading is very nearly uni¬ 
form. It will be recalled that impulse and pressure 
were both arbitrarily reduced by 25 per cent to allow 
for the nonuniformity of pressure over the entire tar¬ 
get. For distant charges this overestimates the reduc¬ 
tion and for near charges it probably underestimates it. 



X theoretical 

□ 8 LB TNT (AREA A) 

■ 64 LB TNT (AREA A) 

O 8 LB TNT (AREA B) 

• 64 LB TNT (AREA B) 

© 216 LB TNT (AREA B) 

O 512 LB TNT (AREA B) 

O 1000-LB 6P BOMB (AREA B) 
(540 LB 50/50 AMATOL) 

© 1000 LB TNT (AREA B) 

(S) 2000-LB GP BOMB (AREA B) 
(1080 LB 50/50 AMATOL) 


Figure 4. Front-wall shots. Deflection of front walls 
as function of a . 





































PART VI 


A TTA CK 


confidential! 















































































Chapter 16 

TARGET ANALYSIS AND WEAPON SELECTION 


M odern warfare is a specialized branch of engi¬ 
neering, and the proper prosecution of a war 
requires that available weapons be used at the highest 
efficiency possible under the prevailing operating con¬ 
ditions. The objective of the attacker is to inflict the 
maximum of damage with a given expenditure of 
effort. His tools are the various weapons developed 
by his technicians and supplied by his industry. It is 
desirable (1) to have efficient weapons, (2) to have a 
sufficient but not excessive selection of weapons, (3) 
to use weapons as effectively as possible, and (4) to 
know the effectiveness of the weapons used. 3 

i6i INTRODUCTION 

In order to make intelligent weapon selections one 
must know the characteristics of the weapons and 
understand the mechanisms by which they inflict 
damage on a target. In this chapter, first the charac¬ 
teristics of the most common weapons are briefly de¬ 
scribed, then each of the usual mechanisms of damage 
is discussed from the point of view of efficiency of the 
weapon. In Section 16.9 this information on weapons 
and mechanisms of damage is used to make detailed 
analysis of and weapon selection for several typical 
target types, and this section serves to illustrate the 
application of the principles described in the earlier 
sections of this chapter. The chapter is concluded by 
a few suggestions for further work on the effects of 
weapons on targets. 

The most widely used report of Division 2 is the 
looseleaf notebook Weapon Data — Fire, Impact, Ex¬ 
plosion. This notebook consists of Weapon Data Sheets 
containing quantitative information on the character¬ 
istics of weapons, the mechanisms by which they act 
on targets, and the selection of weapons for attack of 
certain target types. The final edition of this notebook, 
published as OSRD Report No. 6053, is reproduced 
as part of Chapter 19. Frequent references to individ¬ 
ual Weapon Data Sheets are made throughout this 
chapter, and the sheets should be used as supplements 
to the material presented here. 

A thorough understanding of the behavior of weap¬ 
ons requires knowledge of the fundamental phenomena 

a Pertinent to joint Army-Navy Projects AN-23, AN-28, 
AN-29 and to Navy Project NO-267. 


of explosions and terminal ballistics as described in 
earlier chapters of this volume. References to perti¬ 
nent sections of these chapters will be made, and al¬ 
though the present chapter can be studied independ¬ 
ently, it is suggested that the reader make himself 
familiar with the more important points of the earlier 
chapters. 

16.2 EFFECTIVENESS OF WEAPONS 

During World War II considerable attention was 
given to the effectiveness and the proper use of 
weapons. This study was started by the British, with 
interest originally on defense in various civil and mil¬ 
itary establishments, and was eventually concerned 
with air, land, and sea warfare. Before the entrance of 
the United States into World War II, studies, like¬ 
wise for defense, were initiated at Princeton at the 
request of the Army Corps of Engineers. As World 
War II progressed, there was a continued change of 
interest and eventually, the work at Princeton under 
Division 2 was primarily concerned with aerial attack. 
However, other methods of attack are discussed in this 
chapter. The following aspects of this work were most 
important: (1) the continued acquisition and corre¬ 
lation of information on the effectiveness of aerial 
weapons based on the experience of the British under 
German attacks, the results of tests of weapons in 
Britain and in the United States, and the examination 
and study of the effects of Allied bombing; (2) the 
preparation and distribution of data sheets on the 
characteristics and performance of various weapons 
(see Chapter 19) ; (3) the training of operations ana¬ 
lysts in methods of target analysis and weapon selec¬ 
tion (see Chapter 18) ; and (4) collaboration with the 
Joint Target Group (AC/AS Intelligence) in pre¬ 
paring recommendations for the aerial war in the 
Pacific, and with the United States Strategic Bomb¬ 
ing Survey in drawing conclusions from the European 
theater. 

16 . 2.1 Methods of Studying Effectiveness 

of Weapons 

To use his weapons efficiently, the attacker must 
know the effectiveness of the weapons against various 
types of targets. Two methods have been used to study 

305 


roNni'EvnAj, 






306 


TARGET ANALYSIS AND WEAPON SELECTION 


the effectiveness of weapons: (1) synthesis of the ef¬ 
fects of the weapons on separate components of struc¬ 
tures, as determined by special tests, into a composite 
picture of the expected damage to the complete struc¬ 
ture; and (2) study of damage caused in actual 
attacks. The first method has the advantage of appli¬ 
cability to a wide variety of targets, and the disad- 
vantage of such complexity for most structures that 
it is difficult to use. The second method has the ad¬ 
vantage of giving direct information, and the disad¬ 
vantages of difficulty in determining the extent of the 
damage to enemy targets, and uncertainties in using 
the results to predict damage to a different type of 
target. A combination of the two methods, using one 
to supplement the other, has been found to be most 
effective. 

Synthesis of Effects on Structural Components 

Model- and full-scale tests have been made to de¬ 
termine the effects of explosion, fragments, fire, and 
other mechanisms of damage on various components 
of structures such as columns, beams, roofing, floor 
slabs, and wall panels. The results of such tests can, 
in principle, be used to predict the effect of any 
weapon on a structure having components of known 
characteristics. This type of engineering analysis has 
been attempted for industrial buildings, but, except 
for special cases, the complexity of the targets and 
the interrelations of the various types of damage have 
made the problem too difficult for ready solution. 

Damage involving only one simple component of 
a target, such as the perforation of armor plate or 
concrete slabs, or the cratering of open ground, can 
be studied by direct and simple experiment, and the 
results can be applied to predicting damage to actual 
targets. 

Study of Damage in Actual Attacks 

Many studies have been made of the damage suf¬ 
fered by targets under attack by various weapons. 
Bombing attacks have been made on enemy installa¬ 
tions, and by study of aerial photographs taken be¬ 
fore and after the raid skilled photointerpreters can 
make very good estimates of the damage. The methods 
used in photointerpretation studies must be checked 
by intelligence reports on enemy-held targets and by 
detailed study when such targets fall into our hands. 
Ground surveys of the damage received by enemy fac¬ 
tories, cities, and military installations have been 
made after these targets were in the hands of our 
own forces. This method of evaluating the effective¬ 
ness of weapons has a weakness in that the targets 


have usually been attacked by several weapons and 
it is frequently extremely difficult to attribute damage 
to a specific weapon. 

Studies have been made by constructing models 
or copies of enemy installations and attacking these 
with the weapons to be evaluated. This method yields 
very useful information for attacking specific target 
types. 

Studies of British buildings damaged by German 
air raids have been made, and where the size and type 
of weapon can be determined these yield useful in¬ 
formation. One important function of these damage 
studies has been to check the methods used in photo- 
interpretation by estimating the damage to the same 
structure by both ground and aerial surveys. 

Controlled Experimental Attacks. A direct compar¬ 
ison of the effectiveness of different bombs can be 
made by selecting several enemy targets as nearly alike 
as possible and attacking each target with one of the 
weapons to be evaluated. By a study of aerial photo¬ 
graphs taken before and after each attack, the relative 
effectiveness of the weapons can be determined. This 
method of studying the effectiveness of weapons has 
the advantage of damaging enemy targets and avoids 
the necessity of constructing prototypes. It has the 
disadvantage of relying entirely upon photointerpre¬ 
tation for the evaluation of damage. 

Combination of the Two Methods 

As stated above, the best method of studying the 
effectiveness of weapons is a combination of methods 
(1) and (2). Knowledge of the performance of ex¬ 
plosives, the distribution of fragments, the ability of 
a missile to perforate a target, and other action of 
weapons on targets can be used to interpret the dam¬ 
age observed in terms of the characteristics of the 
weapon. Sufficient information on the fundamentals 
of weapon performance and the various mechanisms 
of damage possible with each weapon will enable one 
to correlate the observed damage from a number of 
different attacks and to draw general conclusions that 
may be used in planning future attacks to utilize 
the capabilities of the weapons in the most effective 
manner. 

16.3 TYPES OF WEAPONS — THEIR 
CHARACTERISTICS 

In order to evaluate the performance of weapons, 
the characteristics of the weapons must be known. 
Weapons may be used for explosive effect, for perfora- 




TYPES OF WEAPONS—THEIR CHARACTERISTICS 


307 


tion or penetration (sometimes followed by explo¬ 
sion), for fragmentation, lire starting, or other effects. 
Airborne weapons, artillery and naval guns, and 
special-explosive weapons will be described separately. 

16 31 Airborne Weapons 

High-Explosive Bombs 

High-explosive [HE] bombs (see Weapon Data 
Sheet lA3a* of Chapter 19) are of several types, the 
main difference being in the strength of the case. 
Bomb cases must be able to withstand the impacts to 
which they are subjected, for if a bomb case is rup¬ 
tured before the explosive detonates a low-order ex¬ 
plosion is likely to result. Low-order explosions are a 
relatively slow burning of the explosive and have very 
little effect compared to that of a proper high-order 
explosion. 

Bombs that are to be used for penetration of resist¬ 
ant targets must have strong bodies, and the thick¬ 
ness of the case required for this strength leaves room 
for only a small quantity of explosive. Bombs that 
explode on contact or in the air need a body only for 
handling and so may have very thin cases, leaving 
room for a large quantity of explosive. These extremes 
and intermediate types of bombs may be described 
by the charge-weight ratio, which is the weight of the 
explosive charge divided by the total weight of the 
filled bomb. 

Light-Cased [LC] Bombs. Light-cased bombs have 
a thin case and a charge weight ratio of about 80 per 
cent. The thin case cannot withstand severe impact 
and the bombs must be fuzed to explode instantane¬ 
ously on contact with a light surface or to explode in 
the air above a target. As shown below in Section 
16.5.1, bombs that damage a target by exterior blast 
are more efficient in large sizes than in small sizes; 
consequently, LC bombs are made only in large sizes. 
They should be used wherever maximum explosive 
effect is desired and penetration is not necessary. 

General - Purpose [CP] Bombs. General - purpose 
bombs have cases somewhat thicker than those of LC 
bombs and a charge-weight ratio of about 50 per cent. 
The case is strong enough to withstand impact on 
most industrial construction and the bombs can pene¬ 
trate into soil without deformation or rupture of the 
body; however, GP bomb cases will break up if the 
bombs are dropped on heavy concrete slabs (see Weap¬ 
on Data Sheet 2Cla in Chapter 19). General-purpose 
bombs are available in a wide range of sizes. Since 
they can withstand impacts they can be used with 
delav fuzing. 

*/ o 


Semiarmor-Piercing [SAP] Bombs. Semiarmor¬ 
piercing bombs have heavy cases and a charge weight 
ratio of about 30 per cent. The cases have sufficient 
strength to perforate medium armor or reinforced 
concrete without deformation. These bombs can be 
used with delay fuzing for attacks on targets protected 
by medium armor or reinforced concrete. 

Armor - Piercing [AP] Bombs. Armor - piercing 
bombs have very heavy cases and contain only a 
small quantity of explosive. The charge-weight ratio 
is usually 10 to 15 per cent. These bombs are designed 
to perforate heavy armor plate without deformation 
or rupture of the case, and should be used with delay 
fuzing for attacks on targets protected by heavy armor. 

Incendiary Bombs 

Incendiary bombs (see Weapon Data Sheets lA3b, 
lA3c of Chapter 19) are of two types: the intensive 
type and the scatter type. Bombs of the intensive type 
burn as a unit and confine their intense heat to a 
relatively small area. They are usually small (2 to 10 
lb) and are dropped in clusters. Bombs of the scatter 
type are somewhat larger than those of the intensive 
type and are usually dropped singly. These bombs 
explode on impact and throw chunks of gasoline gel 
or other sticky highly inflammable material in all 
directions. The purpose of incendiary bombs is to start 
fires, and the choice of one or the other type depends 
on whether chunks of burning gasoline gel scattered 
over a small area or a number of smaller bombs scat¬ 
tered over a wider area will be more effective. 

Incendiary Bomb Clusters. The small intensive- 
type incendiary bombs are packed in clusters that may 
be loaded on aircraft like the larger bombs. These 
clusters may be quick-opening or aimable: the quick¬ 
opening clusters open a short distance below the air¬ 
craft and the small bombs are scattered over a wide 
area, while the aimable clusters are dropped from high 
altitudes and open at an altitude of about 5,000 ft, 
scattering the bombs over a relatively smaller area. 

Special-Purpose Bombs 

In addition to the HE and incendiary bombs de¬ 
scribed above, there are several types of bombs de¬ 
signed for special purposes (see Weapon Data Sheets 
lA3a*, lA3d of Chapter 19). Some of these are the 
fragmentation bombs, depth charges, and aerial tor¬ 
pedoes described below. Other special-purpose bombs 
such as chemical bombs and pyrotechnics are not 
discussed here since they are not used to create physi¬ 
cal damage. 

Fragmentation Bombs. Fragmentation bombs have 


i t'll.'HVI ! \l| 







308 


TARGET ANALYSIS AND WEAPON SELECTION 


a fairly thick steel case that is broken up into small 
pieces, or fragments, by detonation of the explosive 
tilling. The bodies of most types of fragmentation 
bombs are made of a helix of steel bar wrapped around 
a thin inner case; this results in fragments of a fairly 
uniform size dependent on the size of the steel bar. 
Since fragmentation bombs are designed to damage a 
target by missiles from the bomb case, they are always 
fuzed to explode on contact or in the air above the 
target. 

The most used fragmentation bombs are small (4 
to 20 lb) so that a large number of them may be car¬ 
ried to give good coverage over the target area. Some 
targets are only vulnerable to heavy fragments of 
high velocity; for these, larger fragmentation bombs 
are required. The small fragmentation bombs are 
packed in clusters for convenience in loading on air¬ 
craft. 

For low-altitude attack with fragmentation bombs, 
small parachutes must be attached to the individual 
bombs. This slows the descent so that the attacking 
aircraft will be out of the danger zone before the 
bombs explode. 

Depth Bombs. Depth bombs are designed for maxi¬ 
mum underwater-explosive effect. Since the case must 
only withstand impact on water, it is thin and the 
charge weight ratio is approximately 40 per cent. 
Depth bombs carry hydrostatic fuzes that can be pre¬ 
set to cause detonation at any desired depth. These 
bombs may also be equipped with instantaneous nose 
fuzes so that they can be used as small LC bombs 
against surface targets. 

Depth bombs have flat noses to prevent ricochet on 
striking water when dropped from low altitudes, and 
to give a better underwater trajectory. Some of the 
earlier models had round noses, but these can be 
equipped with a flat false nose. 

Aerial Torpedoes. Aerial torpedoes are designed for 
launching from low-flying aircraft. They are similar 
in design and action to ship-launched torpedoes. Aerial 
torpedoes have a nose shaped to prevent ricochet when 
dropped from very low altitudes and to give under¬ 
water trajectories that are near the surface for a long 
distance. 

Aircraft Rockets 

Aircraft rockets were still in the process of develop¬ 
ment at the end of World War II. Most aircraft rock¬ 
ets now in use are essentially artillery projectiles pro¬ 
pelled by rocket motors. They are used in low-level 
or diving attack at short range. Rockets can be aimed 


more accurately than bombs, but have the disadvan¬ 
tage of less explosive effect due to their smaller size. 

Aircraft Gunfire 

The small machine guns carried by most military 
aircraft can be used for strafing attack from low 
altitude, and are effective against light targets that 
are vulnerable to small-arms fire. Guns as large as 
75 mm have been mounted in aircraft to function 
as airborne artillery. The relative merits of these guns 
and airborne rockets have not been determined. 

16 - 3 - 2 Artillery 

Artillery projectiles may be solid steel shot for 
piercing armor, or may be shell filled with explosive 
or other material. Armor-piercing projectiles are de¬ 
signed specifically for holing resistant targets, and are 
frequently equipped with a cap which protects the 
sharp nose in the first stages of impact against hard 
armor. The larger sizes of AP projectiles contain a 
small amount of explosive and can cause some damage 
by fragments after entering a target. Such projectiles 
must have an explosive that is insensitive to impact 
and must be fuzed with a short time delay. 

High-explosive projectiles cause damage by explosive 
effect and by fragments. They must have a body strong 
enough to stand the forces acting when the projectile is 
fired from the gun. Such projectiles are usually fuzed 
for instantaneous action when striking the target. 

Some projectiles have a hollow charge in the nose 
to perforate the target by action of the Munroe effect 
(see Chapter 14). 

There are many other types of artillery projectiles, 
such as smoke shell, illuminating projectiles, etc., but 
since these do not cause physical damage to targets 
they are not considered here. 

Small Arms 

Small arms include rifles, machine guns, and sim¬ 
ilar weapons. They are effective only against light 
targets or personnel. 

Rockets 

A large variety of rockets have been developed for 
use in World War II. Most of these are essentially 
some type of artillery projectile or bomb propelled by 
a rocket motor. Rockets may be fired from individual 
launchers carried by hand or from multiple launch¬ 
ers carried by trucks, tanks, or small ships. Rockets 
may have solid heads for piercing targets, explosive 
heads, or may have a hollow charge in the head for 
holing the target. (See Chapter 14.) 


COXFIDENTIAl* 







EFFICIENCY OF WEAPONS—MEAN AREA OF EFFECTIVENESS 


309 


Very large rocket projectiles have been used in 
World War II, the most striking example being the 
Y-2 rocket employed by the Germans. This weapon 
carried a large explosive charge and was essentially 
an LC bomb with rocket propulsion. 

16 33 Special-Explosive Weapons 

There are many types of special-explosive weapons 
(see Weapon Data Sheets lA7a, lA7b of Chapter 19). 
Most of these are explosive demolition charges de¬ 
signed for some special purpose. Demolition charges 
come in a wide variety of sizes and may be combined 
into very large charges. There is great flexibility in 
their use subject to the limitation of hand placement. 

Line Charges 

Snakes are demolition charges built into a line 
charge several hundred feet in length. They may be 
pushed by tanks or propelled by a rocket motor. The 
shape of these charges makes them suitable for clear¬ 
ing paths through obstacles and mine fields. Line 
charges of less explosive power may be made of Ban¬ 
galore torpedoes or braided Primacord. These may 
be used to clear narrow paths through light obstacles 
such as barbed wire. 

Beach Clearance 

A variety of special demolition charges have been 
developed for clearing mines and obstacles from 
beaches preliminary to a landing operation. Many of 
these devices are described in the references listed on 
Weapon Data Sheet 6D2 of Chapter 19. 

16.4 EFFICIENCY OF WEAPONS —MEAN 
AREA OF EFFECTIVENESS 

To compare the efficiencies of various weapons in 
damaging a target, some quantitative measure of the 
efficiency is needed. It would be desirable to measure 
the damage in terms of loss in effectiveness of the 
opposing forces, loss in productive capacity, destruc¬ 
tion of stores and materiel, or other factors which are 
the ultimate objectives of both strategic and tactical 
attack. These factors are difficult to measure quickly 
and accurately, so the physical damage to the target 
is usually measured as it has been found to be related 
to these quantities. Such important factors as loss in 
productive capacity can be estimated from the physi¬ 
cal damage to the target, but such estimates are not 
included here. 


I6.4.1 Mean Area of Effectiveness— 

Efficiency 

In bombing attacks the physical damage to the tar¬ 
get is usually measured in terms of the area damaged 
to a specified degree, and the efficiency is measured by 
the mean area of effectiveness [MAE]. This quantity 
is the average expected area of damage for one bomb, 
divided by the weight of the bomb, and is usually 
expressed in acres per ton or thousands of square feet 
per ton of bombs. b The radius of damage is the radius 
of a circle of area equal to the average expected area 
of damage (MAE times weight of bomb). Since the 
damage area is not exactly circular, one expects to 
find as much damaged target at distances greater 
than the radius of damage from the bomb as there is 
undamaged target at distances less than the radius of 
damage from the bomb. 

The MAE is a measure of the efficiency of the bomb 
on a weight basis. Bombs having large MAE values 
will cause large areas of damage per ton of bombs 
dropped on the target area, and by consideration of 
the loading characteristics of aircraft (see Section 
16.6.1) the MAE may be used to determine the most 
efficient bomb in terms of area damaged per aircraft. 

For a single bomb striking the target, the average 
area damaged is the MAE times the weight of the 
bomb. If a large number of bombs are dropped with 
random distribution in the target area, the fraction 
/ of the target expected to be damaged is given by 
(because of overlapping) 

/= l — ( 1 ) 

where M is the MAE, D is the density of bombing in 
weight per unit area, and e = 2.718 • • • is the base of 
natural logarithms. For nonrandom bomb distribution 
the relation is more complicated. 

For some types of damage, MAE values can be de¬ 
termined from a knowledge of the action of the bomb; 
for example, the MAE for cratering is the area of 
the crater divided by the weight of the bomb. For 
other types of damage the mechanism of damage is 
complex and more accurate values of the MAE are 
determined by analysis of data from actual bombing 
raids. For example, if an attack has been made on a 
rail yard, reconnaissance photographs will show the 

b Some references use MAE in square feet per bomb to 
describe the average area damaged per bomb. Such values 
must be divided by the weight of the bomb to be consistent 
with the MAE values used here. Some of the Weapon Data 
Sheets of Chapter 19 use MAE defined as area per unit weight 
and others use area per bomb. In each case it is clear which 
definition is used. 


coyriDi yrrAf. 










310 


TARGET ANALYSIS AND WEAPON SELECTION 


number of cars present and the number of cars dam¬ 
aged, determining the fraction / that are damaged. 
The area of the rail yard and the number of bombs 
falling within the yard can also be determined from 
photographs, and determine the bombing density D. 
Using these value of / and D the value M of the MAE 
may be calculated by equation (1). If a large quantity 
of such data is available, the average of such computa¬ 
tions is quite reliable. 

For many mechanisms of damage, the average ra¬ 
dius of damage per bomb can be expressed as some 
power of the weight of explosive charge. If the radius 
of damage is proportional to w p , where w is the weight 
of explosive, the area of damage is proportional to 
w 2p and the MAE, or area of damage divided by the 
weight of the bomb, is proportional to Rw 2p ~ x , 
where R is the charge weight ratio of the bomb. There¬ 
fore, for bombs of the same type, having the same 
charge weight ratio, the MAE is an increasing or de¬ 
creasing function of the weight of explosive, depend¬ 
ing on whether p is greater or less that 0.5. If the 
MAE is an increasing function of the weight of ex¬ 
plosive, the greatest efficiency is obtained by using 
large bombs; if it is a decreasing function of the 
weight of explosive, the greatest efficiency is obtained 
by using small bombs. Thus a knowledge of the values 
of the exponent p and the minimum size of bomb that 
will produce some damage can be used to determine 
whether large or small bombs are the more efficient, 
and that is frequently all that is needed to make a 
weapon selection. If p = V 2 , the MAE is not depend¬ 
ent on the weight of the charge. 

# 

Probable Damage 

The probable damage to a target can be estimated 
from the value of the MAE of the particular bomb 
and target combination considered. 

For estimating probable damage, targets may be 
divided into two types: those targets, usually small, 
that can receive the desired damage by a single bond) 
hit; and those targets, usually large or composed of 
many small targets, that require many hits if the 
desired damage is to be obtained. There are many 
intermediate types falling between these extremes, 
but only the two types will be considered in detail. 

Individual Targets. If a target can be damaged to 
the desired extent by a single hit, the probability of 
causing at least this damage is the probability of ob¬ 
taining at least one hit on the target with the proper 
bomb. The probable area of damage is the MAE times 
the weight of the bomb. For some individual targets, 


such as bridges, the probable damage depends upon 
whether or not a hit is obtained, and the expected 
area of damage has little meaning. 

Individual targets may be attacked by single air¬ 
craft, by several aircraft making successive attacks, 
or by small formations of aircraft. The type of attack 
used should be that requiring the least force for a 
given probability of a hit. 

Large or Compound Targets. Large targets or tar¬ 
gets composed of many individual units are usually 
attacked by a formation of aircraft dropping bombs 
in a more or less uniform pattern. The size of the 
bomb pattern depends on the type of formation and 
method of dropping. This method of attack applied 
to very large target areas is called area bombing. 

A typical example of bombing of a compound target 
is an attack on an industrial area containing several 
buildings. If the same type of bomb is carried by each 
of the aircraft the expected fraction of damage to 
each building is given by equation (1) where M is 
the MAE of the bomb for the building and D is the 
density of bombing. The expected area of damage to 
an individual building is the expected fraction dam¬ 
aged times the area of the building, or expected area 
damaged equals 

AJi = A 1 (l — e~ M i D ) , (2) 

where A 1 is the area of the building and M 1 is the 
MAE of the bomb used in the building considered. 
Some of the buildings will suffer more damage than 
predicted and others will experience less damage, but 
the expected area damaged in each building is given 
by equation (2). The total expected area of damage 
for the entire target area may be determined by apply¬ 
ing equation (2) to each of the buildings and sum¬ 
ming the results for the entire target system. Such a 
procedure will tend to average out the individual vari¬ 
ations from building to building, the averaging being 
better for larger target areas, and if the values of the 
MAE and the bombing density are accurately known 
this gives a reliable picture of the overall damage to 
the target system. 

The calculations described above assume that the 
density of bombing is uniform over the entire target 
area, which of course implies that the uniform pattern 
of bombs must cover the entire area. If the bombing 
density is not uniform, equation (2) may be applied 
to each individual building, using the values of M and 
D for that building, and the total expected area of 
damage will be the sum of the individual expected 
areas for all buildings. 




DAMAGE MECHANISMS 


311 


Most industrial targets contain individual compo¬ 
nents of different importance. The expected area of 
damage for each component may be computed by equa¬ 
tion (2) and weighted by multiplying this value by 
some numerical measure of the importance of the 
target. For example, if a target component of area A 1 
has an importance I 19 then 

Weighted expected area of damage = I 1 A 1 f 1 , (3) 

and a measure of the effectiveness E of the attack is 

„ IiA 1 f 1 + I 2 A 2 f 2 + C 3 A 3 / 3 + •■' 

E = -, (4) 

I 1 A 1 + I 2 A 2 + 7 3 A 3 -1- 

where both numerator and denominator are summed 
for all components of the target. The numerical val¬ 
ues for the importance of the different target compo¬ 
nents must be assigned by someone familiar with the 
details of the target being attacked. The relation be¬ 
tween the effectiveness E and the actual effect on the 
target, such as loss of productive capacity of an in¬ 
dustrial target or decrease in defensive strength of a 
military target, can only be determined by a large 
amount of experience and data. 

165 DAMAGE MECHANISMS 

A knowledge of the various mechanisms for damag¬ 
ing targets is essential for making weapon selections 
or critically evaluating damage, and in many cases 
such knowledge is all that is needed for weapon selec¬ 
tion. The most important mechanisms for damaging 
targets are air blast, confined blast, underground ex¬ 
plosion, underwater explosion, fragmentation, and 
fire. Each of these will be considered separately here, 
with particular attention to bombing problems; how¬ 
ever, the principles given here may be applied to any 
weapon causing damage by one of these mechanisms. 

1651 Air Blast 

When a bomb detonates in air (see Chapter 2), the 
very rapid expansion causes a compressional wave of 
great intensity and very abrupt rise, called a shock 
wave , to spread out from the source of the explosion 
with a velocity initially much greater than the veloc¬ 
ity of sound. This shock wave is characterized by a 
very sudden rise in pressure to the peak pressure, then 
a gradual decrease from this maximum value to a 
pressure below atmospheric pressure, followed by an 
increase to atmospheric pressure as shown in Figure 1. 
As the weight of the explosive charge is increased, 
the distance at which a given peak pressure of the 


shock wave occurs increases as the cube root of the 
charge-weight. At distances from two bombs which 
are proportional to the cube roots of the charge 
weights, the pressures will therefore be the same but 
it is found that the positive impulse will be greater for 



Figure 1 . Shock wave due to explosion in air, showing 
change in pressure with time. 


the larger charge by the ratio of the cube roots of the 
charge at these scaled distances. Furthermore, the 
peak pressure and particularly the positive impulse is 
larger at equal charge-weight for bombs which have 
light cases than for bombs having heavy cases. 

Air blast damages a target by action of the shock 
wave on the target. If the shock wave strikes an ob¬ 
ject that will break very quickly, damage will occur 
if the peak pressure is sufficient, and the duration of 
the wave is not important. If the target is yielding, 
as are most buildings, with a characteristic period 
long compared to the duration of the shock wave, then 
the shock acts on the target for its full duration and 
damage is due to the momentum given to the target. 
This type of damage is a function of the positive im¬ 
pulse of the shock wave, which is the time integral 
of the excess above atmospheric pressure from the be¬ 
ginning of the shock to the time at which the pressure 
first falls to atmospheric pressure. The positive im¬ 
pulse is shown by the shaded area in Figure 1. Weap¬ 
on Data Sheets 3A1, 3A2*, 3A2a, and 3A3 of Chapter 
19 can be used to predict the peak pressure and posi¬ 
tive impulse as functions of weight of explosive charge 
and distance from explosion. 

For bombs having 8,000 lb or less of ordinary ex¬ 
plosive the duration of the shock wave is usually much 
less than the natural periods of normal structures, 
and damage is due to the impulse exerted by the blast 
rather than to the peak pressure of the shock wave. 
It has been found experimentally that the distance 
from an explosion at which a given impulse is pro- 


CONFIDENTIAL, 



















312 


TARGET ANALYSIS AND WEAPON SELECTION 


duced increases roughly as the % power of the weight 
of explosive. Applying the reasoning of Section 16.4.1 
with p = %, one sees that the area within which the 
impulse equals or exceeds a given value is proportional 
to the y 3 power of the weight of explosive; thus the 
MAE for damage due to impulse, or effective area per 
unit weight, is approximately proportional to Rw i/j 
where R is the charge-weight ratio of the bomb and 
w is the weight of explosive charge. Since bombs hav¬ 
ing a large charge-weight ratio also use the explosive 
more efficiently (Chapter 2) the increase in efficiency 
is even greater than indicated here. One sees that for 
greatest efficiency in damaging a target by action of 
the impulse of the shock wave, bombs having large 
charge-weight ratio and large weight of explosive 
charge should be used. The LC bombs have these char¬ 
acteristics and are recommended in all cases where 
external air blast will be the most effective damaging 
agent. Instantaneous fuzing must be used to ensure 
detonation before breakup. 

Airburst Bombs 

The distance over which the impulse exerted by the 
blast wave exceeds a given value can be increased by 
detonation of the bomb above ground (see Chapter 2 
and Weapon Data Sheets 3A7, 3A8, 3A9 of Chapter 
19). Special fuzes must be used to obtain airburst. 

165 2 Confined Blast 

In some instances it is desirable to have a bomb det¬ 
onate inside a building to cause damage by confined 
blast. Since LC bombs can not perforate any but very 
light roofs the GP bombs should be used, with short 
delay fuzing to cause detonation inside the building. 
The reasoning given in Section 16.5.1 still applies and 
large bombs are more efficient than small bombs up to 
the size that will completely destroy an entire unit. 

At present, it is not possible from theory to predict 
whether confined blast with small bombs or external 
blast with large bombs is the better choice. However, 
operational data on Japanese targets indicates that 
4,000-lb bombs, instantaneously fuzed, are more effec¬ 
tive than 500-lb GP bombs with short delay fuzes 
against aircraft factories and similar structures. 

Penetration into Structure 

Case Strength. In order to cause damage by con¬ 
fined blast, a bomb must penetrate into the target (see 
Chapters 6, 7, 8, 9). This requires perforation of a 
structure that may be very light, in the case of a fac¬ 
tory or warehouse, or very heavy, in the case of a forti¬ 
fication. Weapon Data Sheets 2C1-2C8 of Chapter 19 


give information on the perforation of various mate¬ 
rials by bombs and projectiles, and may be used to 
select a weapon capable of reaching the interior of the 
target. In general, LC bombs can be used only for 
extremely light roofing, GP bombs can be used for 
ordinary construction, SAP bombs are needed for 
unusually heavy industrial construction, reinforced- 
concrete fortifications, and lightly armored targets, and 
AP bombs are needed against heavily armored targets. 

Explosive Sensitivity. Some explosives are very sen¬ 
sitive to impact and will detonate when the weapon 
strikes a target, regardless of the fuze delay. More in¬ 
sensitive explosives must be used for filling weapons 
that are to penetrate into a target before exploding. 

16 5 3 Underground Explosion 

When a bomb or shell explodes underground (see 
Chapter 3) the case expands and breaks as in air, but 
the expansion is slower because of the surrounding 
earth. A roughly spherical compression wave called an 
earth shock wave is generated, by the expanding case 
and by continued pressure of the gaseous products of 
explosion, and travels out into the surrounding me¬ 
dium in all directions, decreasing in intensity as it does 
so. When this earth shock wave reaches the surface it is 
reflected, lifting and cracking the soil and projecting 
a large mass of broken soil into the air. Except in very 
deep explosions a crater is formed and becomes par¬ 
tially filled with the broken earth that falls back al¬ 
most vertically. The soil near the explosion is perma¬ 
nently displaced, and transient displacements may oc¬ 
cur at some distance from the explosion. 

Targets can be damaged by displacement of the 
foundation, by earth shock damage to underground 
walls, or by cratering. All these effects can be caused 
by underground explosions. General-purpose bombs 
can penetrate into the ground without damage to the 
case and should be used with the proper fuze delay to 
cause detonation at the desired depth. 

Cratering 

Many targets can be damaged by cratering (see 
Weapon Data Sheets 3Bla*, 3Blb of Chapter 19). 
Experiments have shown that all dimensions of a 
bomb crater are approximately proportional to the % 
power of the weight of explosive; thus the diameter of 
a bomb crater is proportional to w%, the plan area is 
proportional to and the MAE for area cratered is 
proportional to Rw~%, by the reasoning given in Sec¬ 
tion 16.4.1. This means that for maximum area cra¬ 
tered per unit weight of bomb, small bombs of large 






DAMAGE MECHANISMS 


313 


charge-weight ratio should be used. General-purpose 
bombs are the bombs of greatest charge-weight ratio 
that can penetrate into soil without deformation. Fuze 
delays of 0.01 sec for the 100- to 500-lb GP bombs and 
0.025 sec for the 1,000- to 4,000-lb GP bombs allow 
enough penetration for satisfactory crater formation. 
If the soil is resistant to penetration longer delays are 
satisfactory, but for soils allowing deep penetration 
longer delays may result in camouflet or incomplete 
craters. 

Reasoning similar to the above shows that the vol¬ 
ume of a crater is proportional to the weight of explo¬ 
sive. Therefore, if the objective of an attack is to cra¬ 
ter large volumes instead of large areas, the efficiency, 
or volume per pound of explosive, is practically inde¬ 
pendent of the weight of the charge. This means that 
GP bombs of any size may be used with no great dif¬ 
ference in efficiency of forming large crater volumes. 

There is no available data to show whether scaling 
laws applied to craters of ordinary bombs can be used 
to predict crater formation by bombs containing very 
powerful explosives. 

Displacement of Structural Components 

Building columns and foundations, small bridge 
piers, and similar structural components can be moved 
by motion of the foundation soil, and such displace¬ 
ments may weaken the structure sufficiently to cause 
collapse or to require demolition (see Weapon Data 
Sheet 3B2 of Chapter 19). The required displace¬ 
ments can be caused by underground explosions in 
many cases. 

Experiments have shown that the radius from an 
underground explosion at which a given surface dis¬ 
placement is attained increases about as the 0.45 
power of the weight of explosive for GP bombs up to 
2,000 lb in weight. Applying the reasoning of Section 
16.4.1 one finds that the efficiency, or lethal area per 
unit weight, is proportional to Rw~ 0A and the great¬ 
est efficiency will be obtained by using small bombs of 
large charge-weight ratio, provided that the bomb is 
large enough to cause the desired displacement. How¬ 
ever, the exponent of w is so small that intermediate 
bomb sizes may be used with no great loss in efficiency. 
General-purpose bombs should be used to insure pene¬ 
tration into the soil without damage to the case, and 
should be fuzed with sufficient delay to allow enough 
penetration for a well-tamped explosion, but the fuze 
delay must not be too great or the explosion will occur 
too deep to cause much displacement near the surface. 
Fuze delays of 0.01 sec for the 100- to 500-lb GP 


bombs and 0.025 sec for the 1,000- to 4,000-lb. GP 
bombs are satisfactory for most purposes. 

Damage to Underground Walls 

Targets having underground walls can be damaged 
by earth shock acting on the walls (see Weapon Data 
Sheet 6A5* of Chapter 19). Experiments have shown 
that the radius for damage by earth shock is not a sim¬ 
ple power function of the weight of explosive. How¬ 
ever, graphical analysis of the data from a large num¬ 
ber of tests shows that the optimum size of bomb for 
damaging a wall of thickness t ft is that giving a 
scaled thickness t/w* of 0.4 to 0.5, where w is the 
weight of explosive in pounds. The analysis also shows 
that for bombs smaller than this size the efficiency de¬ 
creases very rapidly with decreasing weight of charge, 
while for larger than the optimum size bombs the effi¬ 
ciency is almost as great as for the optimum. There¬ 
fore, the greatest efficiency will be obtained by match¬ 
ing the weight of explosive to the thickness of the un¬ 
derground wall so that t/w* is about 0.4, or w = 16t 3 , 
and by using the first size larger bomb than computed. 
Since the bombs must penetrate into the ground before 
explosion, GP bombs with short delay fuzing should 
lie used. The optimum fuzing should cause detonation 
at about the depth of the center of the wall. 

16 5 4 Underwater Explosion 

When an explosive detonates under water (see 
Chapter 1), the high pressure produced compresses the 
water and causes a compressional wave of high inten¬ 
sity, called a shock wave, to spread out from the source 
of the explosion. This shock wave can cause damage to 
ships or other structures under the water provided 
they are close enough to the source of the wave. Fur¬ 
thermore, the expanding gases from the explosion, 
after producing the shock wave, continue to exert 
pressure on the water, forcing it outward. The com¬ 
pressional wave is, therefore, followed by a flow of the 
water which can be treated as an incompressible flow. 
It is certainly possible that this flow causes damage 
and, in fact, it has been postulated by some that this 
is more important in causing damage than the shock 
wave itself. This is a question which has not been fully 
clarified. The bubble of burnt gas will overexpand, be¬ 
cause of the inertia of the flowing water, and then con¬ 
tract under the influence of hydrostatic pressure. As 
the bubble nears its minimum size, a second compres¬ 
sion wave is emitted which, although much less intense 
than the original shock wave, has a greater duration 
and, therefore, considerable momentum and energy. 




314 


TARGET ANALYSIS AND WEAPON SELECTION 


If the explosion is deep enough, there may be a num¬ 
ber of expansions and contractions with a pressure 
pulse emitted at each minimum. With shallow explo¬ 
sions, these do not occur because the gas bubble reaches 
the surface and vents before the subsequent contrac¬ 
tion can occur. These so called bubble pulses can also 
cause damage under proper conditions. 

When the shock wave strikes a target such as a ship, 
one of several things may happen. The structure may 
fail quickly before the pressure in the shock wave has 
decayed very far. This would be true of a brittle mate¬ 
rial or a system having a very small natural period 
and insufficient strength to resist the high pressure 
(of the order of thousands of pounds per square inch) 
in the shock wave. It may be, however, that the period 
of the structure is longer than the short duration 
of the high-pressure phenomenon, in which case the 
impulse of the wave may be absorbed and may be the 
determining factor for damage. There is one possible 
complication, probably quite important in practice. 
This is that the target, upon being accelerated by the 
pressure wave, may move with sufficient velocity to 
pull away from the water or to pull part of the water 
away from itself, causing cavitation in front of the 
target. This has been clearly demonstrated by photog¬ 
raphy for certain ranges of conditions. In this case, 
it is indicated that it is the energy of the shock wave 
that determines the damage produced. Therefore, there 
are three possible situations, theoretically, regarding 
damage produced by the shock wave; namely, damage 
produced by pressure, by momentum or impulse, or by 
energy. In the first of these cases, the radius of dam¬ 
age would increase as the cube root of the weight, in 
the second as the % power approximately, and in the 
third as the % power approximately. Experimentally, 
all three of these situations can be approximately 
realized but it is not clear which of them is the cor¬ 
rect assumption for normal ship damage. The square 
root law being intermediate between the extremes 
seems to be a good rough approximation as far as our 
present knowledge is concerned. 

Bubble damage, that is, damage caused by the later 
pressure pulses from the oscillating bubble, is believed 
to be important for charges located under the target 
since gravity causes the gas bubble to rise and there 
is also an attraction by the target drawing the bubble 
toward it. These conditions are probably also favorable 
to damage caused by the in compressive flow of the 
water. It is clear that a great deal of work remains to 
be done concerning the mechanism of damage by un¬ 
derwater explosions. 


The case of a bomb does not have to be extremely 
strong to withstand impact on water, and bombs of 
high charge-weight ratio should be used for maximum 
efficiency. Depth bombs have been specially designed 
for use in aerial attack. These bombs have a charge- 
weight ratio of about 70 per cent and are equipped 
with hydrostatic fuzes that can be preset to cause ex¬ 
plosion at any desired depth. 

Special charges for underwater demolition are pro¬ 
vided with waterproof cases and a wide choice of firing 
devices, and may be fitted together to make very large 
explosive charges. 

16 5 5 Fragmentation 

When a bomb explodes in air, the case is broken up 
into a large number of small fragments. Thin bomb 
cases result in very small fragments while thick cases 
result in fairly large, heavy fragments. The fragments 
leave the bomb with an initial velocity that is approxi¬ 
mately inversely proportional to the square root of the 
ratio of the weight of case to the weight of explosive 
charge, and are slowed in their travel through air by 
a resisting force proportional to the average cross- 
sectional area of the fragments and to the square of 
their velocity. When fragments strike a target their 
ability to perforate it is the same as that of any other 
projectile of the same size and shape (see Chapters 6, 
7, 8, and 9), but since fragments from any given 
bomb vary in size and shape the ability to perforate 
must be treated by statistical methods. Most fragments 
from a bomb of average shape are ejected laterally: 
thus the greatest density of fragments is in a thin 
disk-shaped spray around the bomb. 

Thin-cased bombs eject fragments having a higher 
initial velocity than those from bombs having thick 
cases, but the fragments are very light and so are 
slowed in their travel through air more than heavy 
fragments. Furthermore, the fragments are so small 
and light that they have little ability to perforate re¬ 
sistant targets. For these reasons, bombs having thick 
cases are the preferred agents for causing damage to 
a target by fragments. The specially designed frag¬ 
mentation bombs have thick cases. The body is made 
of a helix of square steel bar wrapped around a thin 
inner lining, and on explosion of the bomb this bar 
breaks into large heavy fragments of fairly uniform 
size. Fragments from GP bombs are lighter on the 
average and have such a wide variation in size that 
many small and ineffective fragments are included. 

Bombs must detonate in air if their fragments are 
to be effective, and so should be equipped with install- 


COXFIDEYH.U 







DAMAGE MECHANISMS 


315 


taneous or air-burst fuzes; the air-burst fuzing is pref¬ 
erable for targets having shielding on the sides but 
at present can be used only on certain bomb types. The 
helical case of fragmentation bombs is not designed 
for perforation, so these bombs cannot be used for 
targets under cover. General-purpose bombs must be 
used for fragmentation damage on such targets. 

Small, dispersed, and unprotected targets such as 
personnel, unarmored vehicles, and grounded aircraft 
are vulnerable to fragments. Any fragmentation 
weapon exploding near one of these targets can cause 
damage; the small 20-lb fragmentation bomb is most 
efficient. The larger fragmentation bombs are effective 
at a greater distance from the target but are not as 
efficient in lethal area per unit weight as the small 
bomb. Targets having heavy construction are not eas¬ 
ily damaged by the fragments from the 20-lb bomb, 
and the 90- or 260-lb or other fragmentation bomb 
yielding large fragments must be used. General-pur¬ 
pose and SAP bombs are a good second choice, and 
the GP bomb may be more efficient against some tar¬ 
gets. Targets of very heavy construction are not easily 
damaged by fragments from the standard fragmenta¬ 
tion weapons and should be attacked by using some 
other mechanism of damage. 

i6.5.6 Fire 

Many targets are combustible and where this is the 
case fire is usually the most effective agent (see Divi¬ 
sion 11 STR). Fires can be started by HE bombs or 
by the specially designed incendiary bombs. The in¬ 
cendiary bombs are more efficient in starting fires and 
should be recommended for all targets where fire is 
chosen as the mechanism of damage to be used. How¬ 
ever, the fire-starting capabilities of HE bombs should 
not be ignored in estimating the effects of these weap¬ 
ons on combustible targets. 

Concentration of Eire Sources 

All types of incendiary bombs are effective in start¬ 
ing fires. The choice between the different types of 
bombs depends upon the desired distribution and in¬ 
tensity of sources of fire. The scatter-type incendiary 
bombs are usually filled with a gasoline gel mixture 
that ignites and spreads over a small area when the 
bomb bursts on impact. The small intensive-type 
bombs dropped in aimable clusters that open at an 
altitude of about 5,000 ft spread over a larger area, 
and result in small sources of fire scattered so that for 
each of the present clusters there is one fire source for 
every 2,000 to 5,000 sq ft. These small bombs can also 


be dropped in quick-opening clusters that open a few 
hundred feet below the aircraft and spread the bombs 
over a large area, and for each cluster dropped from 
10,000 ft there is an average of one fire source for 
every 20,000 to 50,000 sq ft. It is seen that these three 
types can be used to cause wide variations in concen¬ 
tration of fire sources. In general, a high concentra¬ 
tion of fire sources is needed for targets that are not 
highly combustible and a wide spread or low concen¬ 
tration is allowable for highly combustible areas. 

Vulnerability of Targets to Fire 

The effectiveness of incendiary bombs in starting 
fires depends to a large extent upon the combustibility 
of the roof of the target (see Weapon Data Sheet 6B2 
of Chapter 19). Once a fire is sufficiently well estab¬ 
lished to cause serious damage, the extent of its spread 
does not depend on the origin of the fire but on the 
combustibility of the roof, the height of the building 
(height of upper story in multistory buildings), and 
the amount and combustibility of the contents. Fires 
are usually limited to the fire division within which 
they start, where a fire division is defined as an area 
of a building separated from other areas by fire walls 
or air gaps. A fire well established in a fire division 
having a combustible roof usually burns out the entire 
fire division, while a fire well established in a fire divi¬ 
sion having a noncombustible roof usually burns out 
only part of the fire division. 

The expected area of damage due to incendiary 
bombs for one fire division of an industrial building 
with a combustible roof is the area of the fire division 
times the probability of starting a fire; for an indus¬ 
trial building having a noncombustible roof the ex¬ 
pected area of damage is that part of a fire division 
that will be burned out by a well-established fire (see 
graph on Weapon Data Sheet 6B2 of Chapter 19) 
times the probability of starting a fire. Thus the MAE 
for damage by fire depends upon the roof, the height, 
the contents, and the area of the fire division. 

Roof. For the purpose of estimating fire damage to 
buildings, roofs may be described as combustible, non¬ 
combustible, or fire-resistant. The type of roof is usu¬ 
ally determined from examination of photographs, 
knowledge of building construction practices, and 
other information. The probability of starting a seri¬ 
ous fire in a building with combustible roof is about 
fifteen times the probability of starting such a fire in 
a building with noncombustible or fire-resistant roof. 

Height. The probability of starting a fire that can 
cause serious damage depends strongly on the eave 


confidential! 







316 


TARGET ANALYSIS AND WEAPON SELECTION 


height of the building or the height of the upper story 
for multistory buildings. Low buildings are much 
more vulnerable to fire starting than buildings with 
high roofs. The relative probabilities of starting a seri¬ 
ous fire in buildings having heights of 10, 25, or 50 
ft are approximately 1, 0.5, and 0.1. For buildings 
having heights of more than 50 ft to the eaves the 
probability of starting a serious fire is negligibly 
small. 

Contents. As would be expected, the combustibility 
of the contents of a building has a great effect on the 
probability of starting a serious fire that will spread 
through the fire division. The combustibility of the 
contents is frequently described by the occupancy rat¬ 
ing, or per cent of the floor area that is covered by 
combustible material. The probability of starting a 
serious fire is approximately three times as much for 
an occupancy rating of 45 per cent as it is for an oc¬ 
cupancy rating of 5 per cent. 

Incendiary Effects of High-Explosive Bombs 

A study of damage to buildings has shown that the 
probability of starting a fire by action of an HE bomb 
is approximately %. Thus for combustible-roof-type 
buildings, the average fire damage due to HE bombs 
is % of the area of the fire division, and for buildings 
having noncombustible roofs the average fire damage 
is % of the area that will be burned out (see graph 
on Weapon Data Sheet 6B2 of Chapter 19). If the 
bomb starts a fire, the structural damage and the fire 
damage will affect the same parts of the building, and 
only the fire damage should be considered. In the five 
out of six instances when no fire is started the struc¬ 
tural damage due to the HE bomb is the only damage 
occurring. Thus the average expected damage for in¬ 
dustrial buildings attacked by HE bombs is % of the 
expected area of structural damage plus % of the area 
expected for fire damage, provided that the area dam¬ 
aged due to one fire is equal to, or greater than, the 
area damaged by one explosion. 

High-explosive bombs may damage the fire wall 
separating fire divisions, and if this occurs fire may 
spread from one division to the next. It is necessary 


that a 500-lb bomb strike within 30 or 40 ft of the wall 
to cause sufficient damage for interdivision fire spread. 

High-explosive bombs may also be used in incen¬ 
diary bomb attacks to cause damage to water mains, 
to block streets with debris, and to hinder and discour¬ 
age fire fighters. 

166 LOADING EFFICIENCY 

The actual combat application of weapons at the 
highest efficiency is not so simple as described in Sec¬ 
tions 16.4 and 16.5. There the efficiency of bombs for 
various mechanisms of damage was described as a 
function of the weight of the bomb, and it was shown 
that if the mechanism of damage to a target is known 
this information alone will often determine the most 
efficient size of bomb and the best fuzing. Such selec¬ 
tions are based on the efficiency in terms of bomb 
weight, and are not necessarily selections of the most 
efficient weapons per plane load. 

16 61 Loading of Bombs on Aircraft 

The following example of the cratering efficiency 
per aircraft will illustrate the importance of the load¬ 
ing characteristics of aircraft in using bombs at the 
greatest efficiency. The diameter of the average crater 
formed in loam soil by bombs detonating at the opti¬ 
mum depth may be determined from Weapon Data 
Sheet 3Bla* of Chapter 19, and the area of the crater 
mav be calculated from this diameter. The first col- 
umn of Table 1 gives the nominal weights of the four 
smallest GP bombs, the second column gives the area 
of the average crater formed by each bomb detonating 
at the optimum depth in loam soil, and the several 
double columns give the number of bombs carried in 
normal loading and the total area cratered (assuming 
no overlap of craters) for some typical bombers. Sec¬ 
tion 16.5.3 shows that the smallest bomb is the most 
efficient for area cratering if the efficiency is measured 
in terms of the bomb Aveight, but Table 1 shows that 
this is not necessarilv true where the efficiency is meas- 
ured in terms of the plane load. The 100-lb GP bomb 
is the most efficient for normal loading on the B-24, 


Table 1. Area cratered per plane load of various general-purpose bombs. 


GP bomb 

Crater 

area 

(ft 2 ) 

B-29 

B-24 

B-17E 

B-17F. Cx 

B-25C, D 

No. 

Area 

(ft 2 ) 

No. 

Area 

(ft 2 ) 

No. 

Area 

(ft 2 ) 

No. 

Area 

(ft 2 ) 

No. 

Area 

(ft 2 ) 

100-lb 

310 

80 

24,800 

52 

16,140 

20 

6,200 

38 

11,780 

12 

3,720 

250-lb 

530 

56 

29,860 

24 

12,720 

14 

7,420 

20 

10,600 

8 

4,240 

500-lb 

830 

40 

33,200 

12 

9,960 

8 

6,640 

12 

9,960 

6 

4,980 

1,000-lb 

1,360 

12 

16,320 

8 

10,880 

4 

5,440 

6 

8,160 

3 

4,080 


I 'IN'HDI \T! AI, 







































FORCE REQUIREMENTS 


317 


B-17F, and B-17G; the 250-lb GP bomb is the most 
efficient for the B-17E; and the 500-lb GP bomb is the 
most efficient for the B-29, B-25C, and B-25D. The im¬ 
portance of considering loading characteristics of air¬ 
craft is shown by the fact that the 1,000-lb bomb is 
more efficient than the 100-lb bomb for normal load¬ 
ing on the B-25, while on a weight basis the 100-lb 
bomb is approximately twice as efficient as the 1,000- 
lb bomb for area cratering. 

16 6 2 Efficiency of Artillery Attack 

The efficiency problems in artillery attack require 
consideration of the rate of fire and mobility of the 
weapons instead of the loading characteristics as con¬ 
sidered for aircraft. The size of gun increases as the 
size of the projectile increases, and the amount of 
explosive carried per shell increases approximately as 
the cube of the projectile caliber. The rate of fire 
usually decreases as the size of the gun increases, and the 
mobility decreases as the weight of the gun increases. 
All of these factors and the operating range influence 
the efficiency of artillery weapons. 

If the objective of an attack is a bombardment of 
a prescribed weight of the explosive per unit area, 
the results can be achieved bv use of a large number 
of small rapid-firing guns operating at short range or 
by use of a smaller number of large guns firing more 
slowly at long range. The small guns and their am¬ 
munition are more mobile, and operational conditions 
may prejudice against exposing the number of and 
positions of the relatively immobile large pieces. How¬ 
ever, the use of large guns makes a heavy attack pos¬ 
sible from a reasonably long range, using a compara¬ 
tively small number of weapons. The decision as to 
which method is the more efficient is a difficult one, 
depending on many factors; a detailed treatment of 
the problem will not be attempted here. 

If the objective of an artillery attack is to perforate 
a resistant target such as a concrete-enclosed gun 
emplacement, the objective can be attained by a 
single direct hit from a large gun or by repeated hits 
in a small area using smaller projectiles (see Sec¬ 
tion 7.2.7). Here, the number of hits required for 
each projectile size can be estimated with some ac¬ 
curacy. The effects of mobility, rate of fire, and other 
factors must be considered as in area bombardment. 

16.7 FORCE REQUIREMENTS 

The force required to cause a desired degree of 
damage to a target depends upon the extent of the 


damage desired, the accuracy of delivery, and the 
MAE of the weapon against the target. If these fac¬ 
tors are known the necessary force can be determined. 

16 71 Bombing Attack 

The force required for a given expectancy of causing 
a desired level of damage to a particular target will 
depend on the type of target, the MAE against this 
target of the weapon chosen, the level of damage 
sought, and the method and accuracy of the attack. 
A target may be a single unit, such as a ship, a bridge, 
or an important fortification, a collection of such 
units, or simply an area vulnerable to attack. Against 
a single target one hit may be sufficient, or a number 
of hits may be needed. In any event, the required num¬ 
ber of hits can be determined. 

Bombing can be by individual aiming of each 
bomb, by individual aiming of each string of bombs 
from a plane, or bombing by groups of planes, each 
dropping a single bomb or a string of bombs upon 
signal from the leader. The probability of achieving 
the desired number of hits with a given force, or the 
number of bombs that must he dropped for a given 
probability of achieving the desired number of hits, 
must be determined by statistical methods. 1,2,3 Briefly, 
the method is as follows: for individual aiming, the 
dispersion of bombs about the aiming point usually 
follows the normal probability curve, which can be 
used to calculate the expectancy of achieving at least 
the desired number of hits. In order to make this 
computation it is necessary to know the accuracy that 
can be expected in the bombing attack; this accuracy 
varies greatly with training, experience, incentives, 
and conditions under which the attack is made, but 
its expected value can be determined for a given 
situation. 

For large formations of planes dropping bombs on 
signal the distribution of bombs differs from the nor¬ 
mal error distribution and for a group so large that 
the size of the bomb pattern is large compared with 
the normal aiming error, the bomb distribution can 
be considered as a random pattern covering the target 
and surrounding area. In this case, the probability of 
getting one hit on a single target entirely within the 
area covered by the bombing pattern is the area of the 
target (or its vulnerable area) times the density of 
bombing, or number of bombs per unit area in the 
pattern. This method of bombing is not economical 
for isolated targets, but may be used against an area 
containing a large number of individual targets. The 
area of the bomb pattern is somewhat greater than the 


CONFIDEXTIAlt 





318 


TARGET ANALYSIS AND WEAPON SELECTION 


size of the formation at the instant of bomb release. 

When the target does not consist of individual units 
on which direct hits must be achieved, but instead 
contains areas of vulnerability to which a single bomb 
can be expected to cause a certain area of destruction, 
equation (1) of Section 16.4.1 may be used to deter¬ 
mine the required density of bombing. This equa¬ 
tion is 

f=l — e- MD , (1) 

where / is the fraction of the target receiving the 
specified degree of damage, M is the MAE of the bomb 
used for the specified degree of damage of the target 
considered, and D (in reciprocal units to M) is the 
density of bombs. Knowing / and M, one can calculate 
the required density. From this density and a knowl¬ 
edge of the method of bombing to be used by the at¬ 
tacking force the number of bombs and planes can 
be determined. This method may be used to determine 
force requirements for attacks on industrial or urban 
areas, airport runways, or other targets where a desired 
level of damage is required but in which there are no 
specific vital spots to which damage must be caused. 

16 7 2 Other Methods of Attack 

The general considerations that have been outlined 
above apply equally to types of attack other than 
bombing, such as artillery, rocket, guided missile, tor¬ 
pedo, and other attacks. For individually aimed weap¬ 
ons the dispersion usually follows the normal error 
curve or an equivalent relation; the numerical factors 
that express the exact shape of this curve depend on 
the accuracy of aiming or control and on any factors 
that can affect the behavior of the weapon between 
the end of aiming or control and the time of striking. 
In any event, a knowledge of the expected distribution 
of hits, obtained from the past performance of the 
weapon and of the size and location of the target 
allows one to calculate the number of tries for a given 
expectancy of obtaining not less than the specified 
number of hits. 

When weapons are used for general bombardment 
or area attack, in which aiming is not directed at in¬ 
dividual targets, the required density of attack is de¬ 
termined by equation (1) for an expected level of 
damage due to attack by weapons of known MAE. 

168 SELECTION OF TARGETS 

Nearly every target contains a number of compo¬ 
nents of differing importance and vulnerability, and 
vulnerable to different damage mechanisms. The se¬ 


lection of the best component to attack must be based 
on the critical nature of the component and its physi¬ 
cal vulnerability to the various damage mechanisms 
available in the form of weapons. A detailed knowl¬ 
edge of the entire target complex is required for in¬ 
telligent target selection. 

16,81 Strategic Targets 

A strategic aerial campaign will be concerned first 
with the selection of target systems for attack, such 
as oil production, transportation, or steel. The choice 
of the systems to receive concentrated attack is made 
at the highest levels, on the basis of the relation be¬ 
tween the effort required and the effect on the enemy. 
Estimates of the effort and effect must be made by 
those familiar with weapon analysis and with the 
whole internal economy of the enemy. 

Every target system contains a large number of 
components of varying vulnerability to attack. The 
selection of the particular components of a system to 
be attacked in order to achieve the desired effect on 
the svstem is normally made at field command level, 
again on the basis of analyses by weapon analysts and 
economic analysts. The components chosen must, of 
course, be those for which the least effort is needed 
for the required effect. The number and choice of com¬ 
ponents of targets depend primarily on three kinds 
of facts: the relative importance of the components 
to the functioning of the system, the physical vulner¬ 
ability of the components to damage, and the ease 
with which they can be hit. Although certain compo¬ 
nents of a system may be absolutely vital to its opera¬ 
tion they may be so well protected and difficult to hit 
as to make very unsatisfactory targets. 

Consider, for example, the planning of attacks on 
transportation. All existing means of transportation 
must be examined. It may be that all will require at¬ 
tack in order to reduce the flow of material to its des¬ 
tinations ; on the other hand it may be that all supplies 
are controlled at some point by a particular system 
and that the desired effect can best be attained by 
attacks on this system only. In attacking a particular 
system it is essential to examine it carefully in order 
to select those parts of it on which to concentrate. 
In the case of rail transportation, for example, there 
are fuel or power supplies, locomotives and rolling 
stock, and right of way. Locomotives can be damaged 
while idle or while in operation and their repair and 
maintenance facilities can also be destroyed. Rolling 
stock can be attacked in large concentrations in freight 
yards. In attacking the right of wav it is usually de- 


ICON RPEXTIAL, 





WEAPON SELECTION 


sirable to select the bottlenecks that are by-passed 
with the most difficulty and are most difficult to re- 
pair. The choice of target points will depend on the 
time for which operation is to be stopped. 

Several typical strategic targets are discussed from 
the point of view of vulnerability and weapon selec¬ 
tion in Section 16.9. 

168 2 Tactical Targets 

A tactical attack is intended to be followed imme¬ 
diately by an advance of one’s own forces into enemy 
territory or to interfere with the enemy’s attempts to 
advance. In either case the objective is to destroy or 
damage fortifications or other defenses, transportation 
and communication facilities, and military supplies. 
The weapons and methods of attack are basically the 
same as in strategic operations, although they may 
be used under somewhat different conditions. The se¬ 
lection of targets according to importance, vulnera¬ 
bility, and ease of hitting must be made, using the 
principles discussed for strategic targets. The prin¬ 
cipal difference between strategic and tactical opera¬ 
tions is in the length of time involved, the former 
being concerned with months and years, the latter 
with hours and days. 

The attack of several typical tactical objectives is 
discussed from the point of view of physical vulnera¬ 
bility and weapon selection in Section 16.9. 

169 WEAPON SELECTION 

The broad general principles governing the selec¬ 
tion of weapons to be used are similar for both strate¬ 
gic and tactical objectives. The primary concern must 
always be the efficiency, or damage for the effort 
expended. 

The choice of bomb and fuze for the most efficient 
aerial attack on a target can frequently be made from 
a knowledge of the mechanism for obtaining the de¬ 
sired damage. The difficulty in making a weapon selec¬ 
tion on this basis is the choice of a target and the 
choice of damage mechanism. The choice of a target 
must be made by using all available information and 
should include consideration of the vulnerability of 
the different targets to bombing. Once a target has 
been selected the type of damage desired must be 
decided upon. Where a target can be damaged by 
several mechanisms, the types of damage and the rela¬ 
tive efficiencies of the different mechanisms must be 
compared. 


319 

In this section, weapon selection for aerial attack 
on typical military targets, transportation targets, 
and industrial targets will be described. 

1691 Military 7 Targets 

Military field targets differ from other targets in 
that the attack is always tactical and never strategic. 
The objective is temporary or permanent neutraliza¬ 
tion of the installations. 

Small, Lightly Protected Targets 

Small, lightly protected targets 4 are vulnerable to 
almost any explosive weapon detonating near them, 
and can be damaged by various missiles (see Weapon 
Data Sheet 6D3 of Chapter 19). If the targets are 
small and widely dispersed, the most efficient weapon 
for attack would be one just large enough to destroy 
one target provided that the aiming accuracy were 
such that a single shot could be reliably expected to 
hit the target. This is actually never the case so that 
the choice between many small weapons and a few 
large ones depends entirely on the MAE of the weap¬ 
ons. If the MAE (per ton) is larger for the large 
weapons and the given type of target, then a few large 
bombs will be more efficient than many small ones and 
vice versa. This is a very important point which has 
often been confused, so that an example may be in 
order. Suppose that it is important to destroy a 
small wooden shack by liigh-altitude attack. Since, in 
this type of attack, there is very little probability 
that any individual bomb will strike the target, all 
that can be done is to drop a considerable number of 
bombs which will form in a more or less random 
pattern which should blanket the target. Therefore, 
the chance that the target will be destroyed is the 
chance that at least one bomb falls within a critical 
distance of the target, this distance depending upon 
the size of the bomb and the strength of the target. 
If, for purposes of illustration, it is assumed that the 
target will be destroyed by a 100-lb bomb falling less 
than 20 ft away or by a 4,000-lb bomb exploding less 
than 150 ft away, the problem is equivalent to the 
following one: 

A number of circles equal in radius to the destruc¬ 
tive radius of the bomb are dropped at random over 
the target. What is the probability that at least one 
of these circles will cover or touch the target? It 
turns out that this probability is given by equation 
(1) where / is in this case to be interpreted as the 
probability of destruction of the target. In this equa¬ 
tion, M is the MAE, that is the area of the circle 


Confidential 








320 


TARGET ANALYSIS AND WEAPON SELECTION 


within which damage is to be expected divided by 
the weight of the bomb and D is the density of bomb¬ 
ing in terms of weight per unit area. If the same 
total weight per unit area is dropped, the choice be¬ 
tween the larger and the smaller bomb will depend 
upon the value of the MAE. If the figures given above 
are correct for the given target, then in this case the 
larger bomb would be superior since its MAE is, in 
this example, larger. This will not always be the 
case. For example, if the target were protected by a 
revetment, then clearly the MAE for any reasonable 
size bomb would be the area of the circle of the 
revetment and would not increase as the size of the 
bomb increased. In this case, the smaller bomb is 
obviously indicated. In many cases, such light targets 
are vulnerable to fragments, in which case the frag¬ 
mentation bomb or small-arms bomb can be recom¬ 
mended. If close attack is possible, airborne rockets 
are effective. 

Personnel. Personnel are vulnerable to direct hits 
by projectiles and to near misses by bombs. Men in the 
open or with partial shielding are attacked most effi¬ 
ciently by small fragmentation bombs. Any bombing 
attack is likely to cause personnel to seek cover, and 
a heavy, sustained attack of any kind will tend to 
prevent operation of all but protected gun positions. 

The vulnerability of men to damage by fragments 
from bombs depends on whether they are standing in 
the open, prone in the open, or shielded by trenches 
or other protection. Men standing in the open are 
most vulnerable, of course; men prone in the open 
are much more vulnerable to fragmentation bombs 
fuzed instantaneously than are men in trenches, and 
are about five times as vulnerable to fragments from 
air-burst-fuzed 500-lb GP bombs as are men in 
trenches. Present air-burst fuzes cannot be used on 
small fragmentation bombs, so a direct comparison 
of these and the 500-lb GP bomb is not possible. 

Weapon Data Sheet 6D3 of Chapter 19 gives the 
average lethal area per bomb for various bombs against 
personnel. The average maximum distance for inca¬ 
pacitation is 40 ft for the 20-lb fragmentation bomb 
and 90 ft for the 500-lb GP bomb, where both are 
fuzed for instantaneous detonation. Air-burst fuzes 
should always be used for bombing men in trenches. 

Vehicles. Small unarmored vehicles are vulnerable 
to small weapons, and fragmentation bombs are effi¬ 
cient agents for damaging them in aerial attack. The 
average lethal area per bomb is given for various 
bombs in Weapon Data Sheet 6D3 of Chapter 19. 
The 20-lb fragmentation bombs are the most efficient 


of present bombs if the efficiency is measured on a 
weight basis, and should be used if available unless 
plane loading factors strongly favor other bombs. 
Severe damage can be caused at an average maximum 
distance of 45 ft from a 20-lb fragmentation bomb or 
115 ft from the 500-lb GP bomb. 

Aircraft. Grounded aircraft are vulnerable to dam¬ 
age by fragmentation bombs, strafing, and fire dam¬ 
age due to close hits by gasoline-gel-type incendiary 
bombs. If aircraft are parked in a line so that many 
can be attacked on one run, strafing is effective and 
efficient. In this or any other disposition of grounded 
aircraft in the open, small fragmentation bombs are 
the most efficient on a weight basis. Lethal areas per 
bomb are given in Weapon Data Sheet 6D3 of Chap¬ 
ter 19, which shows that the average maximum radius 
for severe damage is 45 ft for the 20-lb fragmentation 
bomb and about 160 ft for the 500-lb GP bomb. The 
lethal area per pound of bomb, or efficiency, is twice 
as great for the 20-lb fragmentation bomb as for the 
500-lb GP bomb, and the 20-lb fragmentation bomb 
packed in clusters is usually more efficient per plane 
load. 

Aircraft parked in revetted enclosures are shielded 
against fragments from the side, and should be at¬ 
tacked by bombs using air-burst fuzes so that the 
source of fragments is well above the top of the re¬ 
vetments. Small fragmentation bombs are effective 
if enough are dropped to give a reasonable expectation 
of hits inside of the revetments. 

Resistant Targets 

Resistant targets, such as fortifications, covered gun 
emplacements, and protected ammunition stores, are 
not vulnerable to the small fragmentation bombs rec¬ 
ommended above for small, lightly protected targets 
and must be attacked by weapons capable of greater 
effect. 

Gun Positions 

From the point of view of vulnerability (see Weap¬ 
on Data Sheet 6D1 of Chapter 19), gun positions 
may be divided into three types: (1) guns in the open 
with no protective shielding other than that provided 
by the gun mount, (2) guns surrounded by revet¬ 
ments or other protective walls but open on top, and 
(3) guns enclosed by heavy protective construction, 
such as concrete or steel pillboxes, or gun turrets of 
ships. These three types must be examined for their 
vulnerability to the several possible mechanisms of 
damage discussed in Section 16.5. Guns are heavy and 
present a small area and are not vulnerable to air 










WEAPON SELECTION 


321 


blast. They are obviously not vulnerable to damage 
by tire unless a combustible substance such as gasoline 
gel is actually placed on the gun or the ammunition 
stored by the gun can be exploded. This leaves as 
possible mechanisms of damage, underground explo¬ 
sions and direct hits by missiles such as fragments 
or projectiles. The two mechanisms cannot be used 
together, because delay fuzing is needed for under¬ 
ground explosion and instantaneous or air-burst fuz¬ 
ing is needed for effective fragment distribution. The 
more efficient of the two mechanisms must be decided 
upon. 

Open Gun Positions. Open gun positions 5 have no 
protection and are vulnerable to damage by frag¬ 
ments from bombs exploding some distance away. They 
are vulnerable to damage by cratering, earth displace¬ 
ment, or projected debris from cratering in rocky soil. 
The underground-explosion effects are not great ex¬ 
cept in or close to the crater, but the damage by frag¬ 
ments can occur at some distance from even a small 
fragmentation bomb. Therefore, it is concluded that 
fragmentation is the most efficient mechanism of 
damage to open gun emplacements. This is in agree¬ 
ment with the results of a detailed study of vulner¬ 
ability of guns reported in abstract form in Weapon 
Data Sheet GDI of Chapter 19. There it is seen that 
the MAE for damage by fragmentation is roughly 
ten times that for damage by underground explosion. 
This study used data for damage to guns by frag¬ 
ments from GP bombs; similar data for fragmenta¬ 
tion bombs is not available in sufficient quantity for 
detailed analysis. On dividing the lethal area by the 
bomb weight in pounds for MAE comparisons of 
fragmentation damage against guns in the open, one 
finds that for medium (75-mm to 120-mm) and heavy 
(150-mm and larger) guns the 100-lb GP bomb is the 
most efficient, and the 90- and 260-lb fragmentation 
bombs are almost as efficient as the 100-lb GP. Any 
of these bombs, with instantaneous fuzing, may be 
selected for attack, and consideration of the aircraft 
loading of these bombs will enable the most efficient 
bomb per plane load to be selected. 

Weapon Data Sheet GDI does not give numerical 
values for the vulnerability of light (20-mm and 37- 
mm) guns to damage by fragmentation. The bombs 
selected for the medium and heavy guns may be used, 
but since these guns are of lighter construction it is 
reasonable to expect that the smaller 20-lb fragmenta¬ 
tion bomb will also be efficient for attacking light 
guns in the open. If there is no shielding around the 
guns, there is no advantage in using air-burst fuzes. 


Guns of all sizes are vulnerable to direct hits by 
artillery projectiles or rockets. The operational con¬ 
ditions must determine whether this method of attack 
is preferable to bombing. 

Guns in Revetments. Revetted gun 5 positions are 
vulnerable to damage by underground explosion or 
by fragments or other missiles, as are open gun posi¬ 
tions. The important difference lies in the protection 
provided by the revetment. Experience has shown that 
even large bombs cause no appreciable damage to such 
guns unless they strike inside of the revetted area or 
outside but within about 4 ft of the inside edge of the 
revetment. If the revetment is circular with the gun 
at the center, a bomb having a radius of damage 
smaller than the radius of the revetted area plus 4 
ft will act on the gun as if it were in the open, and 
a bomb having a radius of damage equal to or greater 
than the radius of the revetted area plus 4 ft will 
have a lethal area equal to the revetted area plus the 
area of a band 4 ft wide drawn around the revetment. 
This means that the largest efficient bomb will be that 
bomb having a radius of damage equal to the radius 
of the revetment plus 4 ft. The only instance in which 
larger bombs would be more efficient is with air-burst 
fuzing for detonation above the level of the revetment 
so that the protection provided is nullified. In the 
case of guns in revetments, as for guns in the open, 
the radius of damage by fragments from a bomb hav¬ 
ing instantaneous fuzing is greater than that for 
damage by underground explosion of the same bomb 
with delay fuzing. 

The values of MAE per bomb for unserviceability 
and for temporary unserviceability due to fragment 
damage are given for several bombs and for different 
sizes of revetted gun emplacements in Weapon Data 
Sheet GDI of Chapter 19. Dividing these values by 
the bomb weight for comparison on a weight basis 
indicates that for light guns the 20-lb fragmentation 
bomb is the most efficient instantaneously fuzed bomb 
for 20- and 30-ft diameter positions, and is slightly 
less efficient than the 500-lb GP bomb fuzed for air 
burst; the 90-lb fragmentation bomb and 100-lb GP 
bomb are of about equal efficiency, and are a better 
selection than any of the other bombs listed, includ¬ 
ing the 500-lb GP bomb with air-burst fuzing. 

Similar computations for fragmentation damage to 
medium and heavy guns in revetted positions give the 
same results, except that the 90-lb fragmentation 
bomb and 100-lb GP bomb have about the same 
efficiency, on a weight basis, as the 20-lb fragmenta¬ 
tion bomb for small positions. There is not much data 



322 


TARGET ANALYSIS AND WEAPON SELECTION 


on damage to heavy guns, but the larger fragmenta¬ 
tion bombs are probably more efficient than the 20- 
lb bomb for attack on heavy guns having thick steel 
parts. 

The efficiency comparisons above are for efficiency 
in terms of area of damage per pound of bomb. The 
efficiency in terms of area damaged per plane load 
must be determined by a further calculation using the 
areas given in Weapon Data Sheet 6D1 and the meth¬ 
od of calculation described in Section 16.6.1. 

Enclosed Gun Positions — Fortifications. Strong 
points of resistance frequently have gun positions en¬ 
closed in protective structures of armor or reinforced 
concrete. 6 Such structures are vulnerable to damage 
by underground explosion and are also vulnerable to 
damage by projectiles or bombs that perforate the top 
or side walls and detonate inside, damaging the gun 
or other mechanisms by heavy fragments. Both at¬ 
tacks require delay fuzing, but cannot be made with 
the same weapon without loss in efficiency of one or 
the other mechanisms; perforation requires the 
strength available only in thick bomb or projectile 
cases, and the consequent low charge-weight ratio is 
inefficient for underground explosion. Instantaneously 
fuzed bombs making direct hits on the roof can cause 
damage by contact explosion, but this damage is minor 
in comparison with the damage due to delay fuze 
action of the same bomb. 

The most severe damage can be caused by a bomb 
or projectile perforating the roof or side wall and de¬ 
tonating inside the structure. SAP or AP bombs are 
required for all but thin fortification roofs, and AP 
projectiles should be used in attacking the side walls. 
Less rugged bombs or projectiles are likely to suffer 
case failure and fail to perforate. Weapon Data Sheets 
2C1 and 2 Cl a of Chapter 19 may be used to deter¬ 
mine the smallest bomb or projectile capable of per¬ 
forating concrete of known strength and thickness, 
and Weapon Data Sheets 2C3 and 2C5* may be used 
to select the smallest weapon capable of perforating 
a known thickness of armor plate. The area of the tar¬ 
get vulnerable to such an attack by bombing is the 
inside plan area of the structure, and since almost any 
explosive weapon capable of perforating the roof and 
detonating inside will destroy or severely damage the 
gun or other mechanism, the probability of neutraliz¬ 
ing the position is the probability of obtaining a per¬ 
forating hit in this area. 

Delay-fuzed bombs striking outside a reinforced- 
concrete structure but close to the side walls may 
breach or collapse the walls by transmission of the 


shock of the explosion through the soil. The damage 
is not so severe as that caused by perforation plus 
subsequent internal explosion, but may be quite suffi¬ 
cient to neutralize the position. Weapon Data Sheet 
6A5* of Chapter 19 may be used to determine the 
radius of damage to underground reinforced-concrete 
walls by underground explosion; the curve marked 
breaching should be used in making estimates of vul¬ 
nerable area, and any lesser damage resulting from 
detonations farther from the wall should be consid¬ 
ered a bonus. The area vulnerable to such an attack 
is roughly a band around the outside of the structure, 
having a width equal to the radius of damage. The 
shape of this area around corners of the structure 
must be estimated, and the band may be of varying 
width due to different thicknesses of the side wall. 

Figure 2 is a schematic diagram of a typical rein- 
forced-concrete fortification and shows the areas vul¬ 
nerable to bombing attack by perforation of the roof 
and by earth-shock damage to the side walls. Approxi¬ 
mately, the probability of a hit within either area is 
proportioned to the area. To determine the more effi¬ 
cient of the two methods of attack the vulnerable 
areas per plane load of bombs must be determined. 
For bombs capable of perforating the roof, the vulner- 



VULNERABLE TO 
PERFORATION 


VULNERABLE TO 
EARTH SHOCK 




tL 


CONCRETE 

WALLS 


Figure 2. Reinforced concrete fortification, showing 
areas vulnerable to bombing attack. The inside plan 
area is vulnerable to perforation by bombs. The outside 
area, having width equal to the radius of damage, is the 
vulnerable area for earth shock damage to the side walls 
of the structure. The shape of this area near corners 
must be estimated. 


\ ON FIDEXTIAIi 

























WEAPON SELECTION 


323 


able area is the inside plan area of the target pins the 
area vulnerable to earth-shock damage by the same 
bomb (since both use the same fuzing). The area 
vulnerable to earth-shock damage alone for bombs 
that cannot perforate the roof is determined as indi¬ 
cated above. These may be compared for all possible 
bomb selections to find that bomb for which the target 
has the largest vulnerable area per plane load. For the 
usual type of structure, it will be found that the most 
efficient bomb is the smallest bomb capable of perfo¬ 
rating the roof. 

Since the damage due to explosion in earth near 
the target is not so severe as damage due to perforation 
and explosion, it may be desirable to make the compu¬ 
tation described above with weighted values for the 
different types of damage. For example, if the earth- 
shock damage is considered half as desirable as the 
damage by perforation, all areas for earth-shock dam¬ 
age should be halved in the computation of efficiency. 

Other Resistant Targets. Other types of resistant 
targets are protected ammunition stores, command 
posts, armored vehicles, etc. Any resistant structures 
built of reinforced concrete may be analyzed for attack 
by the method used above. Underground structures 
may be attacked by earth-shock action against the 
walls or roof or by perforation of the composite roof 
of concrete covered with soil. (See Composite Targets 
in Section 9.3.1.) It must be remembered that earth 
shock can act on the roof as well as on the side walls, 
and that a bomb striking the roof but failing to per¬ 
forate usually comes to rest in a position suitable for 
a tamped side-on contact explosion, with possibilities 
of severe damage. 

Armored vehicles are vulnerable only to direct hits 
or very near misses by bombs. They are such small tar¬ 
gets that direct hits by bombs are difficult to obtain, 
and they can usually be attacked more efficiently by 
rocket fire from aircraft or by artillery fire. 

Military Obstacles 

There are many types of military obstacles, varying 
in resistance from light wire barricades to heavy con¬ 
crete and earth antitank walls. Most obstacles are vul¬ 
nerable only to direct hits or very near misses, and are 
so small that hits are difficult to obtain by bombing 
or artillery fire. Hand-placed demolition charges are 
the most effective method of dealing with obstacles, 
but this technique cannot be used at a distance. 

Wire Barricades. Paths through barbed-wire bar¬ 
ricades can be cleared by dropping a line of instan¬ 
taneously fuzed bombs across the barricade, by demo¬ 


lition rockets, or by line charges such as snakes or 
Bangalore torpedoes placed through the wire. Radii 
for clearance of wire by these weapons are given in 
Weapon Data Sheet 6D2 of Chapter 19. Bombs should 
be dropped by flight perpendicular to the line of the 
barricade, using minimum intervalometer setting so 
that the circles of clearance will overlap to provide a 
clear path through the barricade. 

Obstacles. Bombing has proved to be ineffective 
against obstacles of concrete, stone, and steel, unless 
a direct hit is obtained. The clearance of obstacles by 
demolition charges is a specialized technique and will 
not be treated here. The references listed in Weapon 
Data Sheet 6D2 should be consulted. 

TJnderwater Obstacles. Underwater obstacles can be 
cleared by detonation of suitable demolition charges. 
Special charges and techniques have been developed. 
The references listed on Weapon Data Sheet 6D2 
should be consulted. 

Land Mines. Bombing is not a satisfactory method 
for clearing land mines. Paths can be cleared through 
some mine fields by detonation of line charges on the 
ground, small line charges such as the Bangalore tor¬ 
pedo or the infantry snake being used to clear narrow 
paths, while larger line charges carrying several pounds 
of explosive per foot, such as the demolition snake , 
must be used to clear paths for tanks. 

Precise data on the clearance of land mines by line 
charges are not available in enough quantity to allow 
generalizations. The available information indicates 
that for large charges the width of path cleared is 
proportional to the square root of the weight of charge 
per foot, as would be expected from model-law consid¬ 
erations. This means that several parallel line charges, 
properly spaced, can clear a wider path than a single 
charge having the same total weight of explosive per 
foot. This cannot be carried to the extreme of a large 
number of lines of small explosive content, however, 
since a certain minimum weight of explosive per foot 
in each line is necessary to detonate the mines. 

The distance from an explosive charge at which 
land mines will be detonated depends, among other 
things, on the sensitivity of the mine to shock and its 
depth of burial. One rarely knows what type of mines 
are to be cleared or the depth of burial, so the choice 
of explosive weapons for clearance is at best a guess. 
The radius of clearance is not definite, but is usually 
given as the distance at which 50 per cent of the mines 
will be detonated. Some live mines are always left in¬ 
side this radius. Mines near the limiting radius of 





324 


TARGET ANALYSIS AND WEAPON SELECTION 


clearance may have shear wires holding the striker 
pin partially but not entirely cut. Such mines are not 
fired but are left in a more sensitive condition than 
before the attempted clearance. 

Numerous mechanical devices have been developed 
for clearing paths through mine fields. Most of these 
simply apply a heavy load to the ground and cause 
the mines to function normally. Many of these devices 
are quite effective, but have the disadvantage of being 
vulnerable to damage by explosion of large mines. 

16.9.2 Transportation Targets 

The object of attacks on a transportation system 
is to paralyze the system. This may be accomplished 
by destroying or damaging terminals, carriers, trans¬ 
portation lines, or fuel supplies, and may be furthered 
by damaging construction and repair facilities and 
by attacks on plants manufacturing the carriers. Ex¬ 
perience has shown that transportation cannot be 
permanently stopped. The best that can be achieved is 
temporary stoppage, and studies of each individual 
objective will show whether the most efficient method 
is to cause many short delays by light attacks at fre¬ 
quent intervals or to cause long delays by very heavy 
attacks that do not require frequent repetition. 

Rail and Highway Transportation 

Rail and highway transportation can be affected by 
attacking the terminal facilities, the carriers, or the 
roadway. The selection of the most important of these 
requires a detailed knowledge of the transportation 
system, its uses, and the repair and replacement facil¬ 
ities available. The carriers and roadway are usually 
more easily damaged than the terminal facilities. Cut¬ 
ting highways or rail lines is a quick method of stop¬ 
ping the flow of men and supplies, but, except for 
large bridges or tunnels, repairs or bypasses can be 
made quickly. Destruction of railway cars and loco¬ 
motives or vehicles used in highway transportation 
does not cause such immediate results as line cutting, 
but if coordinated with attacks on manufacturing and 
repair facilities such attacks can have a lasting effect 
on transportation. 

Rail Lines — Highways. Traffic may be temporarily 
stopped by direct damage to a rail line 7 or roadway, 
and even though such blocks are quickly repaired the 
right of way is so easily damaged that this method 
of stoppage is important for tactical use (see Weapon 
Data Sheet 6F2 of Chapter 19). Railway lines and 
highways are on the ground, and the obvious mecha¬ 
nism of damage is underground explosion. 


Highways can be blocked by cratering. It was shown 
in Section 16.5.3 that for area covered by cratering, 
small bombs are more efficient on a weight basis than 
are large bombs. The bombs used must be large 
enough to form a crater across the full width of the 
roadway, and the block will not be successful unless 
made in a location where detours are difficult. The 
cratering of roadways on good level ground allowing 
short easy detours has nuisance value only. 

Rail lines can be damaged by underground explo¬ 
sion. It is not clear whether the most useful damage 
is due to cratering or to displacement of the tracks, 
but since the bomb and fuze selection for both mecha¬ 
nisms is the same no choice between the two is neces¬ 
sary. The radii of damage for several GP bombs acting 
on railway track by underground explosion are given 
in Weapon Data Sheet 6F2, and may be used to esti¬ 
mate force requirements for a particular target. Even 
though small bombs cause more area cratered per 
pound than do large bombs, it is usually possible to 
make repairs on several craters simultaneously; thus 
one large crater may require more hours (but less 
man-hours) to repair than several small ones. If a 
line is cut in three or more places and the craters are 
large enough to require heavy equipment for efficient 
repair, it is necessary that some of the damage be 
repaired before equipment can be brought up to the 
others. 

Lines of more than two tracks are seldom completely 
blocked by one bomb hit, and even in cases where all 
lines have been blocked, at least one track can be open 
to traffic in a verv short time. For this reason, bomb- 
ing of rail yards is a poor method of stopping through 
traffic. # 

Long-delay fuzes are not advisable since cutting 
of rail lines is usually a short term tactical maneuver 
and the full force of the attack is needed at once to 
stop the flow of traffic. Delay fuzes of V 2 to 1^ hours 
may be used for nuisance value, but longer delays have 
no marked advantage. For tactical operations the 
enemy would continue to operate over bombs with 
long-delav fuzes. 

Bridges. The most vulnerable points of a railway 
or highway system are the bottlenecks formed by 
bridges 8 or tunnels (see Weapon Data Sheet 6F3 of 
Chapter 19). Bridges are generally the more numerous 
and more easily damaged of the two. Low-level attacks 
may be made against the piers or abutments of bridges, 
using large GP bombs with long-delay fuzing to allow 
the attacking aircraft to escape before the explosion. 
Attacks from high altitudes may be made against the 






WEAPON SELECTION 


325 


bridge superstructure, using large GP bombs with 
very short fuze delays. Direct hits on the superstruc¬ 
ture are then necessary. 

Bridge abutments may be damaged by earth shock 
due to underground explosion behind the abutment 
walls. The radius of damage for various bombs can be 
determined by use of Weapon Data Sheet 6A5* of 
Chapter 19. The bomb must perforate the abutment 
and explode behind, or penetrate the soil behind the 
abutment and then explode. Bridge piers may be dam¬ 
aged or moved, causing the bridge to collapse, by a 
crater undermining the pier or by displacement of the 
pier. Such effects are very difficult to achieve against 
piers anchored to bed rock. Both piers and abutments 
are small targets, requiring high accuracy for success¬ 
ful bombing attack. Such accuracy is usually obtain¬ 
able only from minimum altitudes and so can be used 
only if defenses are light. Large GP bombs (SAP 
bombs for perforation of heavy abutments) must be 
used. 

Bridge superstructures must be attacked by bombs 
fuzed instantaneously or short delay, so attack must 
be made from medium or high altitude for safety of 
the aircraft. Precision bombing is necessary to obtain 
direct hits, and guided missiles may be used to advan¬ 
tage. Through-type bridges, having most of the super¬ 
structure above the roadway, require instantaneous 
or nondelay fuzing to damage the bridge frame. Deck- 
type bridges, having most of the superstructure be¬ 
low the roadway, require a short fuze delay of about 
0.01 sec for detonation of the bomb in the structure. 

Weapon Data Sheet 6F3 of Chapter 19 gives bomb 
and fuze recommendations for attacking a number of 
typical bridge types. This is based on analysis of more 
than 150 incidents of bomb damage to bridges in all 
theaters of operation of World War II. It will be noted 
that for minimum altitude attack on piers and abut¬ 
ments the recommendation assumes that a fighter 
bomber will be used and specifies that the largest 
bomb the aircraft can carry be loaded; for such an 
attack this is obviously the most efficient plane load. 
For medium- or high-altitude attack on bridge super¬ 
structures, the recommendation is generally the 1,000- 
lb GP bomb for single-track bridges and the 2,000-lb 
GP bomb for double-track bridges. At the time this 
Weapon Data Sheet was prepared, the 2,000-lb GP 
bomb was the largest available, having a case that 
could withstand impact on a bridge. The 12,000- and 
22,000-lb bombs have been used successfully against 
very large viaducts, but unless the targets are extreme¬ 
ly wide and heavily built these bombs are excessively 


large. The 4,000-lb GP bomb has not been used in 
combat for attack of bridges, but should prove to be 
a useful weapon for damaging heavy piers or abut¬ 
ments or for high-altitude attack on the superstruc¬ 
tures of bridges more than 16 ft wide. 

Tunnels. Tunnels 9 are bottlenecks in transportation 
systems second only to bridges in importance for at¬ 
tack (see Weapon Data Sheet 6F4 of Chapter 19). 
The blockage of tunnels may be more difficult to repair 
than damage to bridges, but the targets are usually 
less vulnerable. Tunnels may be blocked by collapsing 
the side walls by underground explosion in the soil 
near the tunnel lining; explosions inside the tunnel 
itself cause comparatively little damage. Weapon Data 
Sheet 6F4 gives the maximum distance from the tun¬ 
nel lining at which a bomb causes sufficient damage 
to block passage. The bomb must penetrate through 
soil or rock and then explode near the tunnel, so GP 
or SAP bombs must be used, the SAP bombs being 
required for soft rock. If the tunnel is so deep that 
bombs cannot penetrate to within the lethal distance, 
such attacks are useless. 

Tunnels may also be blocked by taking advantage 
of the steep slopes usually present at the portals and 
causing slides of these slopes. Such tunnel blocks are 
sometimes easy to repair. If the retaining walls around 
the portal are collapsed, the slide may be of such mag¬ 
nitude that reopening of the tunnel will be difficult. 

Landslides. If conditions are favorable, landslides 10 
may be caused in road cuts or on roads along mountain 
sides. Such slides are possible only if the soil is in a 
nearly unstable condition, as after a long rainy spell, 
but may make very successful road blocks requiring 
a long time for repair. The selection of slopes vulner¬ 
able to bombing is a special problem requiring a thor¬ 
ough knowledge of soil stability, and detailed refer¬ 
ences should be consulted. 

Blocking of Bight of Way. Attempts have been 
made to block rail lines and highways by bombing 
of buildings close to the right of way, and in some 
cases large areas of important rail centers have re¬ 
ceived very heavy bombing. Such methods were gen¬ 
erally unsuccessful because there are usually rail and 
highway bypasses around large cities, and the bomb¬ 
ing effort required to block all alternate routes was 
so large as to be inefficient and impracticable. 

Carriers. Railway and highway transportation can 
be reduced by destruction or damage of the carriers. 7 
This is not very efficient in the case of highway trans¬ 
portation because of the large numbers of relatively 
small vehicles, usually dispersed because of variations 


€ OXFID E XTIA It 





326 


TARGET ANALYSIS AND WEAPON SELECTION 


in traffic requirements. Railway transportation can be 
seriously harmed by damage or destruction of freight 
cars and locomotives, the locomotives usually being 
more critical (as well as more difficult to damage). A 
knowledge of the relative availability of freight cars 
and locomotives is necessary to determine which will 
be the more profitable target. 

Strafing and rocket attack are both effective on 
locomotives, especially if they are hit while in opera¬ 
tion so that secondary damage from an exploding 
boiler will occur. Hits with rockets are more effective 
but also more difficult to attain, and of the two meth¬ 
ods strafing is probably preferable with present accu¬ 
racies. Strafing and rocket attack are of little or no 
value against other forms of rolling stock. 

Locomotives and freight cars can be destroyed or 
damaged by bombing, and such attacks are usually 
more efficient when directed against the high concen¬ 
trations of rolling stock common in freight yards. 

Freight Yards. Freight yards 7 are a very good tar¬ 
get if the objective is damage of rolling stock. Freight 
cars can be damaged by blast, fragments, undermining 
by cratering, or by fire. Data to show which of these 
mechanisms is the most efficient are not available, and 
one must rely on analysis of attacks. Such an analysis 
shows that instantaneous fuzing is probably best, in¬ 
dicating that blast or fragmentation is the damage 


mechanism to be preferred. Fuze delays of 0.01 sec, 
however, are almost as effective as the instantaneous 
fuzing and probably cause damage by debris and by un¬ 
dermining of cars. If damage to tracks in the freight 


yards is desirable, the 0.01-sec delay fuzing will serve 
the double purpose of damaging freight cars and 
tracks. The 1,000- and 500-lb GP bombs are both 
effective; the smaller bombs do not cause severe 
enough damage. The 500-lb GP bomb is about 25 
per cent more efficient than the 1,000-lb GP against 
freight cars, and the 1,000-lb GP is slightly more 
efficient than the 500-lb GP in damaging locomotives. 

Radii for different categories of damage to loco¬ 
motives are given in Weapon Data Sheet 6F2 of 
Chapter 19. The MAE can be determined by taking 
the area of a band, having the radius of damage as a 
width, drawn around the locomotive, adding the plan 
area of the locomotive, and dividing this total area 
by the bomb weight. Consequently, the MAE depends 
upon the size of the locomotive. 

Analysis of data on the effects of bombs on freight 
cars has led to an MAE value of 0.29 acre per ton 
for the 500-lb GP bomb and 0.23 acre per ton for 
the 1.000-lb GP bomb, both being for fuze delays of 


0.01 sec and for attack on European-style wooden box 
cars. Both bombs are effective against the shops, con¬ 
trols, and signal equipment, and warehouses usually 
found near freight yards. 

Studies of a number of bombing attacks on freight 
yards in Italy show that with 500-lb GP bombs fuzed 
0.01-sec delay, a bombing density of 1.5 to 2.0 tons 
per acre in the target area is sufficient to disrupt a 
freight yard completely. Obviously, transportation 
facilities which are expected to be captured later 
should not be over-destroyed. 

Repair Facilities. Attacks on railway and highway 
systems should be followed up by attacks on the facil¬ 
ities used for repair of locomotives, freight cars, and 
other equipment. The repair shops are similar to 
machine shops or factories using heavy equipment, 
and should be attacked by the same methods. Attacks 
on heavy industrial plants are discussed in Section 
16.9.3 below. 

Fuel Supplies. All types of transportation require 
fuel for operation, and damage or destruction of these 
supplies can have an important effect on movement 
of materials. 

Air Transportation 

The volume of material carried by air transporta¬ 
tion is usually much smaller than that handled by 
other methods, but the materials carried are frequently 
critical. The attack of aircraft in flight is difficult, 
and there is no roadway to attack, so that efforts must 
be concentrated on airports, fuel supply, and manu¬ 
facture of aircraft. 

At an airport, attacks on runways, grounded air¬ 
craft, repair shops, and fuel storage are all effective. 
These targets are frequently close together, but since 
the damage mechanisms for the various targets are 
different they cannot all be attacked effieientlv by the 
same weapon. Grounded aircraft are attacked most 
efficiently by fragmentation bombs which have no effect 
on runways, while runways and landing areas are most 
efficiently attacked by cratering bombs which have 
comparatively small radii of damage to grounded 
aircraft. 

Strategic bombing with the stoppage of aircraft 
transportation as an objective can be directed at air¬ 
craft production. Fuel production and storage are also 
important targets. The tactical attack of an airfield, 
with temporary neutralization as an objective, can be 
accomplished by first cratering the runways and then 
strafing or using fragmentation bombs to destrov the 
grounded aircraft. 



WEAPON SELECTION 


327 


Runways and Landing Grounds. The obvious mech¬ 
anism of damage to be used in attacking runways and 
landing grounds 11 of airports is cratering by under¬ 
ground explosion (see Weapon Data Sheet 6F1 of 
Chapter 19). General-purpose bombs should be used 
to ensure penetration into the soil without case failure, 
and fuze delays of at least 0.01 sec or more for the 
100- to 500-lb GP bombs, or 0.025 sec or more for the 
1,000- to 4,000-lb GP bombs should be used to allow 
enough penetration for efficient cratering. Since most 
airports are built on a base of well-compacted soil, 
bombs will not penetrate too far for effective cratering 
even with very long fuze delays. 

In planning a cratering attack, one must decide 
whether the objective is maximum area of craters, 
maximum volume of craters, or maximum number 
of craters. A statistical study of actual attacks on 
runways 200 to 300 ft in width shows that an aver¬ 
age of 8 craters per 1,000 ft of length usually leaves 
the runway temporarily inoperative for fighter planes, 
while an average of 5 or less craters per 1,000 ft of 
runway length usually leaves the strip serviceable. 
More than 8 craters per 1,000 ft are needed for wider 
runways. The same study shows that for temporary 
unserviceability the number of craters rather than 
the area or volume cratered is the controlling factor. 
This means that as long as the bomb selected is large 
enough to form a damaging crater in an airport run¬ 
way, the most efficient weapon for temporary tactical 
damage to runways is that bomb that can be loaded 
on aircraft in the largest numbers. All GP bombs, 
from the 100-lb to the largest sizes, cause craters large 
enough to damage runways, and any of them can be 
used with the delay fuzing recommended above. For 
runways paved with concrete more than 9 in. thick, 
the 250- or 500-lb GP bombs are the smallest that 
can be used for perforation of the paving without 
damage to the bomb case. 

If the runways are to be made inoperative for more 
than a few hours, the number of craters is not the 
only criterion for successful attack, although in any 
case at least 8 hits per 1,000 ft of runway length 
(more for runways wider than 300 feet) are needed 
for unserviceability. The repair facilities available to 
the enemy must be considered. The use of small bombs 
results in a larger area cratered per pound of bomb 
than is caused by large bombs, and all GP bombs 
cause about the same crater volume per pound. 
Many small craters can be repaired simultaneously 
by several crews of men, and the small craters can 
usually be repaired without the heavy equipment 


needed for efficient repair of large craters. A com¬ 
promise must be made between the desire for a large 
number of craters to ensure immediate inoperability 
and the desire for large craters (requiring more air¬ 
craft to carry the required number of large bombs) 
needed for long repair times. Whatever the weapon 
selection, the best that can be done is to make the 
runways unusable for the short time needed to re¬ 
pair craters. 

Grounded Aircraft. Bombing and strafing attack 
on grounded aircraft 4 was considered in Section 
16.9.1. Fragments provide the best mechanism of 
damage, and the most efficient present bomb is the 
20-lb fragmentation bomb, fuzed for instantaneous 
action. For aircraft protected by revetments, bombs 
using air-burst fuzes are more efficient. However, air- 
burst fuzes are adapted for use only in large bombs, 
and small fragmentation bombs have efficiency com¬ 
parable to that of larger bombs using air-burst fuzing. 

Buildings — Repair Facilities. Damage to runways 
and landing grounds is always of a temporary nature, 
and damage or destruction of grounded aircraft is 
only effective until the enemy can bring in new planes. 
Both of these attacks are therefore of tactical value 
in that they make an airfield temporarily ineffective, 
but do not have appreciable long-term strategic value. 
More permanent damage to an airport can be caused 
by attacks on the buildings, repair facilities, and 
stores. Such installations are best attacked by the 
methods used for industrial buildings and warehouses, 
discussed in Section 16.9.3. 

Water Transportation 

Water transportation can be affected by attacking 
the terminal facilities and the carriers. Air attacks on 
such objectives do not always yield large dividends 
for the force used because ships are small moving tar¬ 
gets difficult to hit, and docks and harbors are of such 
heavy construction that substantial forces carrying 
large bombs are necessary to cause appreciable dam¬ 
age. However, the importance of water transportation 
makes it an important strategic target. Ships may be 
attacked by gunfire, rockets, and torpedoes, and the 
usefulness of harbors, channels, or even larger areas 
may be very seriously affected by mining. 

Dock and, Harbor Facilities. Dock and harbor in¬ 
stallations are usually so heavy that they are vulner¬ 
able only to direct hits or very near misses by large 
bombs. Warehouses and other buildings near docks 
can be damaged by the methods used for other indus¬ 
trial buildings, and if a large fire can be started great 





328 


TARGET ANALYSIS AND WEAPON SELECTION 


damage can result. Mining of harbor entrances is 
difficult but effective. 

Docks are vulnerable to damage by underwater or 
underground explosion; the latter is undoubtedly the 
more efficient. Large GP bombs with delay fuzing 
should be used. The radius of damage to docks de¬ 
pends upon their size and type of construction and 
each important target should be studied carefully by 
someone familiar with its construction and with the 
effectiveness of bombs. If ships are at the docks at the 
time of the attack, they are an additional target vul¬ 
nerable to the weapons used against the harbor instal¬ 
lations, and if sunk in the harbor they may form effec¬ 
tive blocks to movement of other vessels or to use of 
facilities. 

Ships. Ships 12 can be sunk or severely damaged by 
bombs, torpedoes, mines, and by gunfire or rockets. 
The most effective methods of attack from the air are 
bombing and torpedoes launched from aircraft; oper¬ 
ational conditions frequently determine which method 
is to be used. Unless the target is known before weap¬ 
ons are loaded on a plane, weapon selection for the 
attack of ships is at best a qualified guess. 

Ships are small moving targets difficult to hit from 
the air except by minimum altitude or dive bombing, 
and these methods may result in great losses if used 
against heavily gunned vessels. Unarmored merchant 
vessels are vulnerable to direct hits or very near misses 
by GP bombs fuzed for detonation inside of the ship, 
explosion below the water line and above the keel line 
being the most effective. Discriminating fuzes that 
function with a short delay if the bomb hits the ship 
but will not function on water impact may be used 
with hydrostatic fuzes so that near misses may dam¬ 
age the ship by underwater explosion. The vulnerable 
area for damage or sinking by one or more direct hits 
is the area of the ship as seen from the bomber; using 
the combination of discriminating fuze and hydro¬ 
static fuze gives the added possibility of damage by 
near misses and the vulnerable area is increased by a 
band of small width, drawn around the ship. No ac¬ 
curate information on the width of this band, or near- 
miss distance, is available. To cause optimum damage 
by underwater explosion a bomb must detonate far 
enough below the surface so that the force of the ex¬ 
plosion will not be wasted in the air above. The mini¬ 
mum depths for formation of bubbles by underwater 
explosion, given in Weapon Data Sheet 3C2 of Chap¬ 
ter 19, are satisfactory. 

Most warships and large merchant ships are di¬ 
vided into compartments, and several compartments 


must be flooded to cause sinking. In general, this re¬ 
quires several hits at different points. 

Division 2 has not made a study of the vulnerability 
of ships to bombing attack. A very good study, based 
on a careful analysis of the vulnerability of the various 
types of ships and the probability of obtaining multi¬ 
ple hits that will cause flooding of several compart¬ 
ments, has been made by the Navy. 12 

1693 Industrial Targets 

Each type of industrial target requires special study 
so that bombing efforts may be directed toward de¬ 
struction of the most critical and most vulnerable com¬ 
ponents. Compromises are frequently necessary. For 
example, the air compressors of a steel mill are very 
critical, for if the flow of air to the blast furnaces is 
stopped the furnaces may freeze and be damaged be¬ 
yond repair. These compressors are a small target, dif¬ 
ficult to hit, and are of such heavy construction that 
a direct hit by a very large bomb is necessary to cause 
serious damage. Thus the air compressors, while very 
critical, are a relatively poor target and more loss in 
steel production per sortie can be caused by damage 
to other parts of the steel mill. 

Factory Buildings and Machinery 

Factory buildings 13 can be damaged by external 
blast, confined blast, displacement or undermining of 
the structure by underground explosion, and by fire 
(see Weapon Data Sheets 6B1, 6B2, and Incident 
Summaries of Chapter 19). Machinery and materials 
in the buildings can be damaged by falling debris or 
by collapse of parts of the building, by displacement 
due to blast or earth shock, by fragments, or by fire. 
The area damaged by underground explosion is gen¬ 
erally smaller than the area damaged by air blast from 
the same bomb, and air blast is accompanied by frag¬ 
ments capable of damaging machinery. The most 
promising damage mechanisms for factory buildings 
and machinery are air blast and fire. Fire should be 
chosen as the damage mechanism when attacking com¬ 
bustible buildings or buildings with combustible con¬ 
tents; under all other conditions HE bombs should be 
used for blast effect on the structure and fragmenta¬ 
tion and debris damage to machinery. 

In causing damage by blast it is necessary to decide 
whether internal or external blast is better, since dif¬ 
ferent fuzings must be used. Each has certain advan¬ 
tages and disadvantages. Internal blast, being some- 
wdiat confined, is more destructive to a structure than 
is an equal external blast (see Section 15.2.1 of Chap- 


( OXI'TDEXTTa! 





WEAPON SELECTION 


329 


ter 15). However, on account of that confinement, its 
effect on a nearby structure is reduced. For this reason, 
a bomb larger than needed to damage one structure is 
inefficient if used for internal blast. Bombs must have 
cases heavy enough to perforate roofs without failure; 
this means that about half of the weight of a bomb 
will be wasted so far as explosive power is concerned. 
However, the fragments from the case will be effective 
damaging agents against the contents of most facto¬ 
ries. The delay fuzing required for internal explosion 
means that near misses will crater and will be rela¬ 
tively ineffective in regard to both fragments and 
blast. 

When external blast damage is desired, LC bombs 
with instantaneous or air-burst fuzing are used. These 
give very small fragments and since bombs detonate 
outside of structures the damage to contents from 
fragments is small. Small bombs that make hits on 
structures, being unconfined and detonating at roof 
level, generally do much less damage per pound of ex¬ 
plosive than those that penetrate before exploding. 
For external blast, efficiency of bombs increases with 
size throughout the range of HE sizes that are now in 
use (up to about 8,000 lb of explosive). 

The choice between internal and external blast must 
be made after consideration of all the factors involved, 
particularly the amount and kind of contents, and 
their vulnerability to fragments, the size and strength 
of buildings and their separation. Analysis of attacks 
on Japanese industrial targets indicates that the use 
of large LC bombs for external blast is more efficient 
than 500-lb GP bombs detonated inside the structure. 
This increase in effectiveness should be even more 
marked if air burst were used for the large bombs. 

Bombs fuzed with slight delay for internal blast ef¬ 
fect will cause damage from very near misses, within 
the so-called near-miss distance, in about one out of 
ten cases. For the 500-, 1,000-, and 2,000-lb GP bombs 
against normal light factory construction the near- 
miss distances are respectively 15, 20, and 35 ft. For 
large LC bombs fuzed instantaneously or for air burst 
the effective distance (near-miss distance would be a 
misnomer here) is much greater, being about 80 ft 
for the 4,000-lb LC bomb with instantaneous fuzing. 
The effect of a particular bomb on a particular size 
and type of structure can be expressed in terms of the 
MAE (Section 16.4.1) ; the optimum size of bomb for 
causing structural damage can be determined by com¬ 
paring MAE ? s. However, it must be remembered that 
damage to contents may be more important than 
structural damage, and generally requires fragment¬ 


ing bombs exploding internally except where struc¬ 
tural debris can damage contents, e.g., a heavy roof. 

In general, it is concluded that for small HE weap¬ 
ons (< 2,000 lb) confined blast due to bombs explod¬ 
ing inside buildings is the most effective damage 
mechanism. This requires that the bombs be capable 
of perforating the roof without damage, so GP bombs 
must be used. Fuzing must be of sufficient delay to 
cause detonation below the roof and above the floor 
level, and thus depends on the height of the building. 
Nondelay fuzing causes detonation just below the roof 
and is best for targets whose construction is such that 
a major collapse of the roof can result. A fuze delay 
of 0.01 sec causes detonation 8 to 10 ft below the roof 
and is the best choice for most structures. A fuze de¬ 
lay of 0.025 sec causes detonation 20 to 25 ft below 
the roof and is effective for buildings having roof 
heights of 40 ft or more with machinery vulnerable to 
fragments near floor level, and should also be used for 
multistory buildings. The SAP bombs are necessary 
for attacks against buildings having unusually heavy 
roof construction. (See Data Sheet 2Cla of Chapter 
19.) 

Weapon Data Sheet 6B1 of Chapter 19 has a table 
of MAE’s for several bombs against industrial build¬ 
ings. Values given for the 500-lb GP bomb are deter¬ 
mined by analysis of a large quantity of data, and val¬ 
ues of the 4,000-lb LC bomb are also based on analysis. 
The values given for the 1,000-lb and 2,000-lb GP bomb 
are estimated from the MAE for the 500-lb GP bomb 
on the assumption that the MAE is proportional to 
the weight of explosive charge in the bomb, which has 
been shown by experience to be approximately correct. 
Analysis of recent data indicates that the larger bombs 
are proportionately a little more efficient than the 500- 
lb bomb, so that the MAE values for the 1,000- and 
2,000-lb GP bombs, given in Weapon Data Sheet 6B1, 
should be increased by a few per cent. Furthermore, 
the greater near-miss areas for larger bombs indicate 
an additional superiority, since the probability of an 
effective hit is greater. 

Light machinery within a building may be damaged 
by falling debris if part of the building collapses, and 
most machinery will he damaged by fragments from 
GP bombs exploding inside of the building, although 
effective and simple protection has been obtained by 
concrete walls surrounding each piece of equipment. 
Fragmentation bombs are not normally used with de¬ 
lay fuzing and have comparatively weak cases; hence, 
they are not suitable for creating fragment damage 
within a structure. 


COXEIDEXTIAL 







330 


TARGET ANALYSIS AND WEAPON SELECTION 


Very heavy machinery, as found in some industries, 
is not severely damaged by fragments and does not 
suffer irreparable damage from falling debris unless a 
heavy structural member strikes part of the mecha¬ 
nism. Such heavy equipment can be made inoperative 
by displacement due to underground explosion, but 
this is usually easily repaired. Some types of heavy 
machinery cannot be destroyed by IIE bombs unless 
direct hits are obtained. 

Warehouses—Storage Depots 

Warehouses and other stores of supplies may be at¬ 
tacked using the weapons employed in attacking fac¬ 
tory buildings. The structures are similar and are sub- 
ject to damage by the same mechanisms. As shown in 
Section 16.5.6, the combustibility of the contents of a 
building is a very important item in the starting of 
fires by incendiary bombs and in the spread of these 
fires. If combustible materials are known to be stored, 
incendiary bombs are usually the best choice except 
for buildings having roofs that are highly fire-resistant. 

Domestic Construction 

Residential areas usually consist of a large number 
of very small well-separated structures. Although such 
structures are frequently combustible, each is a sepa¬ 
rate fire division and fires will not generally be spread 
from one unit to the next unless a conflagration is 
started. Small incendiary bombs scattered over the en¬ 
tire areas are the most effective weapon. The structures 
are usually so small that for present sizes of GP bombs 
near-miss damage is comparable to or greater than 
that due to direct hits. Therefore the greatest damage 
per ton of HE bombs will result if large bombs, fuzed 
for air burst, are used. The most effective of the pres¬ 
ent HE weapons is the 4,000-lb LC bomb with air- 
burst fuzing. If GP bombs smaller than the 100-lb 
size or LC bombs larger than the 4,000-lb size are 
developed their performance must be evaluated, that 
of the small GP bombs for direct hits, and of the 
large LC bombs for air burst. 

LTtilities 

Utilities such as electric power, gas supply, water 
supply, sewage systems, and telephone and telegraph 
service are important targets in strategic warfare. At¬ 
tacks may be directed at lines or at sources. The lines 
are usually not attacked as separate targets but are 
damaged as part of a general attack on an industrial 
target or area. Sources such as electric power plants 
and water supply and purification systems are good 
primary objectives. 


Underground Piping. Underground piping, whether 
gas lines, water lines, sewage lines, or telegraph lines, 
is vulnerable to damage by underground explosion. 
Weapon Data Sheet 6E1 of Chapter 19 gives radii of 
damage to cast iron and to ceramic piping as a func¬ 
tion of the weight of explosive charge for bombs ex¬ 
ploding underground. Radii of damage to under¬ 
ground electric cables are not given; these cables are 
usually sheathed in lead, are quite flexible, and have 
been found undamaged even inside bomb craters. 

Overhead Wiring. Overhead wiring is not a satis¬ 
factory target for bombing. Most observed damage to 
wiring can be attributed to debris or fragments. 

Electric Power Plants. Electric power plants are 
usually either hydroelectric or operated by steam tur¬ 
bines. In either case the power plant itself is attacked 
in the same manner as any other heavy industrial 
structure by using large GP bombs fuzed with short 
delay for damaging the buildings by blast and the ma¬ 
chinery by debris and fragmentation. Fragments can 
damage the windings in generators or the motors of 
turbines, and difficult and expensive repairs are neces¬ 
sary if only a few fragments enter one of these ma¬ 
chines. Hydroelectric power plants can be put out of 
operation for long periods by damaging or destroying 
the dams, penstocks, or controls for water flow. The 
penstocks and controls are vulnerable only to direct 
hits, and most dams are exceedingly difficult to dam¬ 
age even with large and special weapons; equivalent 
loss in production of electric power can usually be ob¬ 
tained more easily by other means. 

Transformer Substations. Transformers, switches, 
and other equipment in substations are highly vulner¬ 
able to damage by heavy fragments. A single fragment 
can perforate the case of a large transformer, short- 
circuit the windings, and cause the insulating oil to 
leak out. The entire transformer must be replaced. 
Fragmentation bombs equipped with instantaneous 
fuzes are the best weapon for attacking electric power 
substations or outdoor transformer installations at an 
electric power plant. The small 20-lb fragmentation 
bomb is most efficient for attacking small and medium 
sized transformers; large transformers having thick 
steel cases require the heavier fragments from the 90- 
and 260-lb fragmentation bombs for effective damage. 
GP bombs can also be used. Transformer installations 
are small and therefore difficult to hit in bombing. 
The large numbers of bombs needed for a reasonable 
assurance of several hits require that the resulting 
strategic effects must be compared with the effects of an 
equal tonnage of bombs dropped on some other target. 



WEAPON SELECTION 


331 


Special Industrial Targets 

The discussion of factories and machinery, at the 
beginning of this section, applies to many kinds of in¬ 
dustries operating in ordinary buildings. There are 
many other types of industry, e.g., steel manufacture 
and oil refining, that employ special plants and equip¬ 
ment and therefore need special study and planning 
for a successful bombing attack. Individual vulnera¬ 
bility analysis should be made of all important indus¬ 
trial targets in order to select the best objectives for 
attack and the most efficient weapon for damaging 
these objectives. For some types of assembly and light 
manufacturing, bombing of buildings, as discussed 
above, is satisfactory unless analysis of the target 
shows that special conditions exist. For other types of 
industry, requiring highly specialized construction 
and equipment, a detailed analysis is necessary for 
efficient strategic operations. 

No attempt will be made here to give a detailed 
analysis of a wide variety of targets. One example, 
Japanese steel production, will be discussed and the 
important points in the analysis brought to the atten¬ 
tion of the reader. Similar analyses may be made of 
any other strategic target systems. 

The Japanese Steel Industry. The Japanese steel 
industry was an important strategic target in World 
War JI. Before this war started, steel was produced in 
Japan from imported ores and in Manchuria from 
local ores. Most of the fabrication plants were located 
in Japan proper, and drew on Japanese steel produc¬ 
tion, Manchurian steel production, and imported iron 
and steel for supplies. Soon after World War II 
started, foreign imports of ores and of iron and steel 
were almost entirely cut olf, and the main source of 
supply was the Manchurian ore. 

After the imports of steel were stopped, the capacity 
of the fabrication plants in Japan was much greater 
than was needed to handle the steel produced locally 
and in Manchuria. This meant that steel fabrication 
plants were very poor strategic targets, since the 
work done by any one plant could be transferred to 
another plant with no overloading of facilities. The 
bombing of steel producing units in Japan and in 
Manchuria would have a much greater effect on pro¬ 
duction of finished products. Steel could be produced 
in Manchuria and shipped to Japan, or ores and coal 
could be shipped to Japan for local production. Ap¬ 
proximately 12 tons of ore and coal are needed to 
produce 1 ton of steel, and since shipping was critical 
the effects of destruction of steel furnaces in Man¬ 


churia would be multiplied about twelvefold when 
considered as an effect on production of finished prod¬ 
ucts in Japan. 

This analysis of the wartime Japanese steel in¬ 
dustry is somewhat naive in that all details are not 
fully considered, but a more thorough analysis leads 
to the same conclusion: the greatest loss in finished 
steel products in Japan, for a given bombing effort, 
could be achieved by destruction of steel mills in 
Manchuria, Decent historv has shown this conclusion 
to be correct. 

Bombing of Steel Mills. There are four principal 
operations in the production of steel, and the basic 
pieces of equipment for each operation, in the order 
of the operations, are: 

1. Coke ovens, in which coke is produced from coal 
with various gases as by-products; 

2. Blast furnaces, which are used for the reduction 
of iron ore to relatively pure iron; 

3. Steel furnaces, in which the iron is alloyed with 
other materials, principally carbon, to form steel; 

4. Blooming mills and rolling mills, in which steel 
is rolled to the shapes necessary for structural or 
mechanical use. 

In most steel industries all four of these processes 
are carried out on one site and all are integrated for 
producing a continuous flow of finished steels from 
the raw materials. Each process is dependent on a con¬ 
tinuous and regulated flow of products from the pre¬ 
ceding process. 

However, in the Japanese steel industry the first 
two steps were frequently carried out near sources of 
ore and coal in Manchuria, and the iron produced by 
the blast furnaces was shipped to Japan for conversion 
into steel and rolling into the required structural 
shapes. As stated above, the Manchurian production 
was the most important from a strategic point of view, 
so the primary objectives of strategic bombing of the 
Japanese steel industry should be the coke ovens and 
blast furnaces in Manchuria. These two targets will 
be considered separately below to select the one best 
suited for efficient bombing attack. 14 See Weapon Data 
Sheet 6C1 of Chapter 19. 

Cole Ovens. Steel cannot be produced without coke 
for use in the blast furnaces, so the destruction of 
coke producing facilities directly affects the produc¬ 
tion of steel. From the point of view of bomb damage, 
coke ovens can be classified into two types: the older 
type, which can be repaired after a bombing hit with 
only the directly damaged portions requiring repair; 





332 


TARGET ANALYSIS AND WEAPON SELECTION 


and the modern type, which undergoes excessive crack¬ 
ing as a result of cooling and therefore requires com¬ 
plete relining if cooled for repairs or cooled because 
of loss of control resulting from bomb damage. Dam¬ 
age to the older type of ovens is essentially limited to 
the radius of damage of the bomb, while an entire sec¬ 
tion of the newer type is damaged by a single effective 
bomb hit. Most coke ovens, both older and modern 
types, are built in batteries of four or five sections, 
each section being about 50 ft wide and 100 to 120 ft 
long and made up of some 30 to 40 ovens. The plan 
area for bombing attack is therefore 5,000 or 6,000 
sq ft, although part of this area is masked by control 
equipment and loading chutes. Cooling for repairs, 
repairing the ovens, and reheating may require sev¬ 
eral months. 

The tops of the sections of ovens are made of good 
quality brickwork about 3 ft thick. The 500-lb GP 
bomb is the smallest that can perforate the top without 
damage to the case, and if the top of the section is 
known to be more than 3V2 ft thick the 500-lb SAP 
bomb or the 1,000-lb GP bomb must be used. Delay 
fuzing will assure detonation inside of the oven sec¬ 
tion, and 0.025-sec delay is recommended. A delay of 
0.01 sec is not recommended because some bombs may 
have the fuzing mechanism initiated by overhead 
loading cranes and detonate before reaching the inside 
of the ovens. Since the bombs will be brought to rest 
within the ovens, delays longer than 0.025 sec are 
satisfactory but have no advantage. 

Near misses more than about 2 ft from a section 
of ovens do not cause damage to the ovens. The aux¬ 
iliary equipment may be damaged by near misses or 
direct hits, but since repairs can be made in a much 
shorter time than that required to repair ovens such 
damage is not serious except w r hen it causes loss of 
control of the ovens, resulting in cooling and cracking. 
The important factor is not the area of primary dam¬ 
age but the time required for repair. 

Blast Furnaces. The blast furnace plant consists 
of the furnace, charging equipment and storage and 
mixing bins, hot-blast stoves, blowdng plant, and other 
handling equipment. The blast furnace cannot oper¬ 
ate if any of the equipment related to it is damaged 
or destroyed. Destruction of some of the equipment 
will cause production to stop or to proceed at a re¬ 
duced rate, but the furnace can be emptied and cooled 
slowly without damage. Destruction or serious damage 
to the furnace, all of the hot-blast stoves connected 
to one furnace, or to the blowdng plant can cause op¬ 
erations to stop immediately, with “freezing” and 


consequent complete loss of the furnace. Such dam¬ 
age necessitates abandonment of the furnace and new 
construction requiring several months. 

Blast furnaces cannot be damaged except by direct 
hits of large bombs, exploding inside the furnace. 
Hits on the side of the furnace will ricochet, so the 
area vulnerable to direct hits is the top of the furnace, 
or about 300 sq ft. The 2,000-lb GP bomb is the small¬ 
est bomb that can be expected to cause serious damage; 
a fuze delay of 0.025 sec is recommended to cause 
detonation inside of the furnace. 

Hot-blast stoves heat the air for blast furnace oper¬ 
ation. There are usually four of these, placed close to 
the furnace, but only two or three are used at any one 
time and one stove or connections to stoves at other 
furnaces can keep the furnace in operation while 
emptying and cooling. Therefore all four must be 
destroyed or seriously damaged to put one furnace out 
of operation. The stoves are of heavy construction 
and a direct hit by a 1,000- or 2,000-lb GP bomb, 
fuzed for 0.025-sec delay, is needed for each stove 
that is damaged. Four hits are needed to put a fur¬ 
nace out of operation. Each stove has a vulnerable 
area of about 300 sq ft. 

The blowdng plant furnishes air under pressure 
for operation of blast furnaces, and usually several 
furnaces receive compressed air from one blow r er. Thus 
destruction of one blowing plant may cause freezing 
of several furnaces. The blowdng equipment is of very 
heavy construction and it is unlikely that a near miss 
by a 2,000-lb GP bomb will cause sufficient damage to 
stop or delay blast furnace operations. The target is 
so small that direct hits on the equipment are un¬ 
likely. No incidents of bomb damage to blowdng plants 
have been reported. 

Selection of Target. In the special case of the 
Japanese steel industry, analysis of the industry has 
shown that the best target from an economic point of 
view is the iron production in Manchuria. Further 
analysis of this as a target show r s that the coke ovens 
and related equipment, the blast furnaces and related 
equipment, or both, are suitable targets. Severe dam¬ 
age or destruction of either target will require several 
months for repairs or rebuilding. The coke ovens can 
be damaged by smaller bombs than are needed for 
damage to the blast furnaces and related equipment, 
and present a vulnerable area many times as large. It 
is therefore concluded that the best targets for attack 
are the coke ovens. These present a vulnerable area of 
5,000 to 6,000 sq ft per section and a direct hit by a 
single 500-lb GP bomb, fuzed 0.025-sec delay, will 







RECOMMENDATIONS FOR FUTURE WORK 


333 


cause such damage to oue section that several months 
will be required for repairs. 

1610 RECOMMENDATIONS FOR 

FUTURE WORK 

In any future war, new weapons, more complex and 
more powerful than those used in World War II, will 
be employed. Strategic warfare will probably be much 
more important than tactical operations. The vulner¬ 
ability of targets to new weapons will be so different 
from vulnerability to present weapons that a large 
part of present knowledge of the effects of weapons on 
targets is already obsolete. However, mechanisms of 
damage will not be changed by the introduction of 
new weapons and the principles of selecting weapons 
to act by the most effective mechanism will remain 
the same. 

The directions along which studies of weapon ef¬ 
fectiveness should be continued are not entirely cer¬ 
tain. It is true that present knowledge of the weapons 


used in World War II is far from exact or complete 
and, even though such weapons may soon be surpassed 
by others, there is reason to believe that analyses of 
the data obtained in Europe and Japan will be useful. 
High-explosive and incendiary weapons will continue 
to be effective. It is very probable that their power will 
be improved, and it is certain that methods of delivery 
will be greatly changed. It can be expected that aim¬ 
ing accuracies and velocities of impact will be greater 
in the future than they have been. These considera¬ 
tions will undoubtedly alter some of the recommenda¬ 
tions that appear in this chapter. 

Further study and analysis of the effects of bombing 
in Europe and Japan may be useful. However, the re¬ 
sults of these studies will be of great value only if they 
are interpreted and applied by men trained in the fun¬ 
damentals of terminal ballistics and explosive effects 
and capable of estimating the performance of new 
weapons from a knowledge of the performance of old 
ones. The training of such men, as outlined in Chap¬ 
ter 18, is recommended. 







































PART VII 


LIAISON 































































































Chapter 17 


THE DIVISION 2 TECHNICAL LIBRARY 


17.1 INTRODUCTION 

S ince the principal functions of Division 2 were 
the acquisition, analysis, and distribution of infor¬ 
mation on weapon performance a means of collecting, 
sorting, and preserving the reports containing this in¬ 
formation, especially those reaching the division from 
outside, was of utmost value to it. This need was rec¬ 
ognized soon after the formation of the division, or 
rather, soon after the formation of its predecessor, 
Section B of Division A, NDRC. A library for the use 
of the division was set up at the division office in 
Princeton and made the primary responsibility of one 
man. This library grew rapidly and by the end of World 
War II contained about 20,000 items. Since it played a 
very essential part in the functioning of Division 2, 
and since such a library is an essential part of any 
organization having similar functions, it was felt de¬ 
sirable to describe its operation in this volume. 


17.2 


ORGANIZATION 


The Division 2 library was organized with particu¬ 
lar attention to its ability to assist a search for all 
reports relating to a particular subject. The essential 
need for this was found to be a well-maintained subject 
reference system. Listing merely key words that ap¬ 
peared in the titles of reports was insufficient; instead 
it was necessary to assign the work to a person with 
reasonable acquaintance with the technical field cov¬ 
ered, so that he would be able to make an intelligent 
selection of subject references. In this library the cata¬ 
loguing was done according to the subject classification. 
As an example of the form which that classification 
took, the following were the main categories: 

1000-1999 Weapon Description, 

Impacts, 

Explosions, 

Armor, 

Structural Behavior, 

Materials Testing, 

Experimental Apparatus, 
Miscellaneous. 

The way this was worked out in detail is illustrated by 


2000-2999 

3000-3999 

4000-4999 

5000-5999 

6000-6999 

7000-7999 

9000-9999 


considering a particular number, such as, say 3101; 

3-Explosions 

31—Air Blast 

3101 Blast-Pressure Measurements. 

The fineness with which subject classification is car¬ 
ried out is limited only by the ability of the classifier. 
It was found that for maximum convenience in locat¬ 
ing reports it was well to have not more than a few 
dozen in each subject group so that it would not take 
too long to look through all of the reports of a group. 
In the subject classifications used, it turned out that 
one classification had 300 reports in it and another 
had 200, but few of the others had more than 20 or 
30. No need was found for any particular order within 
a subject group, so that reports were simply added in 
the order received, although provision was made to 
put closely related reports, such as addenda or succes¬ 
sive progress reports, consecutively. Thus each report 
was assigned a number having two parts, the first of 
which indicated the subject group while the second 
indicated merely the number of the report within the 
group. A typical number would be, say, 3101/52, 
which would mean the fifty-second report on air-blast 
pressure measurements. When the next report was 
received on the same subject, it would ordinarily re¬ 
ceive the number 3101/53, but if it was particularly 
closely related to, say, 3101/47 then it would receive 
the number 3101/47.1. 

It was found unnecessary to extend the subject clas¬ 
sifying to the reports within one group, since that 
would make for unnecessarily complicated reference 
numbers, and since each subject group did not contain 
many reports. 

It turned out to be very important not to limit the 
subject classification of a report to its primary subject 
but to make plentiful cross references to subsidiary 
subjects, because seldom is a report found that agrees 
exactly in subject with the breakdown used for clas¬ 
sification but, instead, contains parts of several classes. 
If these subject cross references had been omitted the 
subject index would have been much less useful. For 
the same reason, when a report such as a progress re¬ 
port consisted of several parts by different authors, 
care was taken to catalogue it according to the subject 


• '■M .i'i.VT! 


337 







338 


THE DIVISION 2 TECHNICAL LIBRARY 


of each part, and to prepare author and title cross ref¬ 
erence for each part as well. 

It was found convenient to the operations of the 
library to have a ready means of distinguishing its ref¬ 
erence numbers from others that might be used in 
connection with a report. Thus each of the Division 2 
classification numbers was prefixed by a pair of letters 
to supply this indication. The letters PF (Princeton 
Files) were used, so that a complete number would be 
PF-3101/52. 

Considerable care was taken to see that the cross 
references made were as extensive as possible. Thus 
not only were cross reference cards prepared for the 
author and the title of each report, but cards were also 
prepared for each of the various reference numbers 
that it contained. This was done even though certain 
reports contained fifteen or more such reference num¬ 
bers. The effort was found to be repaid by the greater 
number of times that reports could be located from 
fragmentary information. 

17.3 REPORT ABSTRACTS 

A technical abstract was made of each report as it 
was received. This had a dual purpose; it was used on 
accessions lists which were distributed to the research 
workers in the division to let them know that new re¬ 
ports had been received in their fields, and it also was 
put on the subject reference cards, thus permitting a 
subject search without the necessity of obtaining the 
actual reports from the files or calling them in from 
loan. 

17.4 CONTENTS 

The major supplier of reports to the library was the 
OSRD Liaison Office, which did an excellent job of 
obtaining and forwarding reports secured from the 
various British organizations. Through this means 
were received regularly the reports of the Static De¬ 
tonation Committee and the Anti-Concrete Committee 
of the Ministry of Supply, the Underwater Explosions 


Subcommittee of the Admiralty, and the Research and 
Experiments Department of the Ministry of Home 
Security. Group A of the OSRD Liaison Office per¬ 
formed the same function for reports issued by Ameri¬ 
can Service groups, including intelligence reports in 
the field of the Division. 

These sources were supplemented by information 
especially obtained by Division personnel in the course 
of various foreign missions. Thus early in World War 
11 the Division Chief, during a trip to England, ob¬ 
tained permission to have reproductions made of a 
number of analyses of bomb-damage incidents in Eng¬ 
land prepared by the Ministry of Home Security. Also 
the several operations analysis groups, some of whose 
personnel had been trained by the Division (Chapter 
18), sent back material expected to be useful to the 
Division’s work, and the same was done by several of 
the various bomb-damage surveys. Through these 
sources the library was able to keep abreast of the in¬ 
formation in the field of the Division, generally receiv¬ 
ing reports shortly after they were written. 

175 SECURITY 

One of the problems that required most careful con¬ 
sideration for its solution was that of maintaining ap¬ 
propriate security in the functioning of the library. 
It was found that this could best be solved not by 
limiting the library to coverage of a very narrow field, 
but by having the library cover a broad field, supplying 
to the individual research worker only information 
pertinent to his problem. Thus the librarian would 
have a large enough field from which to locate related 
information for the research worker. 

The accessions lists were handled in a special way 
because of the requirement of security. Instead of put¬ 
ting on one list all reports received by the library, it 
was necessary for the librarian to keep a tabulation of 
the interests of the various workers, and notify them 
only of the various reports in their fields. Thus the re¬ 
port titles and abstracts reproduced were sorted so that 
only appropriate ones reached each individual. 


CONFIDENT.! A|, 





Chapter 18 


TRAINING OF OPERATIONS ANALYSTS 


18.1 INTRODUCTION 

here has been a clear need for men, trained in 
the principles of damage assessment and weapon 
selection, to work with operations officers in combat 
zones and with planning and intelligence organiza¬ 
tions at various headquarters. These men act as con¬ 
sultants in weapon selection and operations planning, 
and aid in evaluating the damage caused by various 
operations. 

As the personnel of Division 2 acquired informa¬ 
tion and experience on the performances of weapons 
it became more and more evident that men with such 
knowledge would be of great use to those engaged in 
planning operations. In late 1942, operations analysis 
sections were being set up at various air force head¬ 
quarters, and Division 2 undertook to find and train 
men in the principles of weapon selection for such an 
assignment. In the spring of 1943 six men were 
brought to Princeton to be trained as operations ana¬ 
lysts ; all were later employed by the air forces as con¬ 
sultants in operations, working with planning groups 
in the theaters. 

The work of this first group of men was so well re¬ 
ceived that there were requests for additional men of 
similar training and abilities. Other groups were 
formed and were trained at Princeton; by August 
1945, five groups had received formal training and 
several men unable to come to the Princeton Univer¬ 
sity Station at the time of one of the regular training 
courses received individual training. Most of the men 
were civilians, although one group was composed en¬ 
tirely of naval officers. 

Approximately forty men received training in bomb 
selection and damage assessment and, except for those 
of the last group, nearly all were assigned to service 
with one of the air forces or with some other organi¬ 
zation where a knowledge of the effects of bombing 
was needed. Men worked with at least eight of the 
various air forces, with the Joint Target Group 
(AC/AS Intelligence), with the Research and Experi¬ 
ments Department, Ministry of Home Security (Brit¬ 
ish), and in various naval organizations. The last 
group of men completed their training in August 


1945. Two of these had orders to report for duty and 
others were awaiting orders when Japan surrendered. 

One man, accompanying landing forces so that he 
could make observations on the effects of bombing be¬ 
fore these effects were erased or changed by clean-up 
operations, was killed in action. The fact that he took 
the risk of going in with a landing force for the op¬ 
portunity of making direct and immediate observa¬ 
tions of the effects of bombing is an example of the 
sincerity and thoroughness of the work of all of these 
men. 

181,1 Liaison Provided by Training 

One important result of sending these trained men 
to the field was the liaison provided between field 
operations personnel and research organizations in 
this country. The men who had been through the 
training program described above were familiar with 
the research activities of various organizations and 
therefore knew where to seek information and advice 
on problems as they occurred, and were receptive to 
such information. Most of the men working on weapon 
selection and damage assessment had the common 
background of the training program and were per¬ 
sonally acquainted with each other. This provided an 
informal liaison between sections, and the men were 
interested in and receptive to ideas developed in sec¬ 
tions other than their own. 

The training program was very useful to Division 2 ,. 
in that reports and personal communications from 
men working in the field provided a contact between 
those engaged in research and those applying the re¬ 
sults of research. Such contact was especially helpful 
in guiding the programs of Weapon Analysis (see 
Chapter 16) and Weapon Data Sheets (see Chapter 
19). 

18.2 THE PRINCETON TRAINING 

PROGRAM 

All men receiving formal training at the Princeton 
University Station went through a six-to-eight-week 
course of study, supplemented by visits and short 
training courses with other organizations. 



CONFfDKXTJAi. 


339 





340 


TRAINING OF OPERATIONS ANALYSTS 


18 21 Selection of Men for Training 

Men to be trained as operations analysts for work 
with the air forces must have good background knowl¬ 
edge of engineering structures, mathematics, and ap¬ 
plied physics. Most of the men selected for training 
were trained as engineers or architectural engineers 
and had some professional experience in one of these 
fields. Men were also selected for emotional maturity, 
physical fitness, pleasing personality, and ability to 
work well with others, because all of these traits are 
important in acting as a field consultant to higher 
echelon combat officers. 

18 - 2 - 2 Training at Princeton 

All the men had a review course in mechanics and 
a special course in mathematical probability and its 
application to bombing problems. The men were 
trained to find and use reference material on weapon 
effects and required to make detailed studies of many 
of the operations reports and damage studies available 
in the Division 2 library. The men received lectures 
on effects of air blast and underground explosions, 
terminal ballistics of armor and concrete, and on the 
effects of weapons on targets. These lectures were 
given by the heads of the several research sections of 
the Princeton University Station who were available 
throughout the course for consultation and guidance 
of further studies. 

Training films, loaned to the station by the Army 
Air Forces, were used for instructional purposes. 

Features of the later training programs were visits 
to various industrial plants under the guidance of a 
structural engineer on the staff of the station. These 
plants were examined for vulnerability to various 
mechanisms of damage by bombing, and the managers 
of the plants discussed the critical nature of certain 
operations and equipment also from the point of view 
of vulnerability to bombing. 

18.2.3 Training by Other Organizations 

All formal training groups, except the first, and 
many of the men who were trained informally received 
additional training by other organizations, although 
no group received training by all of the organizations 
mentioned here. The U. S. Naval Bomb Disposal 
School gave the men a short course on the character¬ 
istics and properties of bombs and fuzes. Division 11, 
NDEC, sent representatives to Princeton to give lec¬ 
tures on the properties and effects of incendiary 
bombs. Several of the groups were given additional 
training in the theory of probability and analysis of 


data by the Applied Mathematics Panel. Many but 
not all of the men received further training at the 
Army Air Forces School of Applied Tactics 
[AAFSAT]. The last group of trainees received in¬ 
struction on rockets and their effects from Division 3, 
NDRC. 

1824 Reference Material 

All men who were trained for operations analysis 
prepared personal notebooks containing the most im¬ 
portant data and other information acquired in their 
training course and in study of reports in the Division 
2 library. All trainees were given a number of reports 
to be used in their future work, and provision was 
made to keep them supplied with revisions and addi¬ 
tions to these reports and with other new information. 
The most important reports given to the trainees are 
found in the bibliography. 2 ' 6 

Most of the men, on completion of their training, 
were assigned to operations analysis sections of the 
Army Air Forces. In the course of their work, these 
men prepared recommendations on bomb selection and 
estimates of bomb effectiveness. These reports were 
distributed among all Army Air Forces operations 
analysis sections. Copies of these reports were received 
in the Division 2 library and were used in training 
new men as operations analysts. 

183 OTHER TRAINING PROGRAMS 

Operations analysis covers a wide variety of sub¬ 
jects, and analysts worked with combat forces in many 
ways in World War II. Only weapon-effects analysts 
were trained at Princeton. Most of the operations ana¬ 
lysts who worked on weapon selection and damage as¬ 
sessment for the armed forces of the United States 
were attached to the Army Air Forces or the Navy; 
two men who had been engaged in research on weapon 
effectiveness at the Princeton University Station of 
Division 2 were attached to the Army Ground Forces 
as operations analysts in weapon effectiveness toward 
the end of World War II, but such work with the 
ground forces never received the interest and support 
given by the air forces. No formal training program 
for Army Ground Force operations analysts was es¬ 
tablished. 

18.3.1 British Operations Analysis 

and Training 

The British had operations analysis sections at¬ 
tached to most branches of their forces concerned with 



RECOMMENDATIONS FOR FUTURE WORK 


341 


combat operations, and used operations analysts to a 
wider extent than did our own forces. Several men 
who had taken the Princeton training course also took 
a training course in bomb selection and bomb damage 
analysis given by the British, and have described this 
course in detail. 1 

184 RECOMMENDATIONS FOR 

FUTURE WORK 

The need for information on the effectiveness and 
efficient use of weapons and the need for men trained 
to use this information has been obvious in World War 
II. In any future war more complex and more power¬ 
ful weapons than are now known will be used, and the 
need for men trained to evaluate the performance and 
to advise on the use of these weapons will be much 
greater than it has been in the past. Any future war 
will require more complete military organization and 
more interdependence between branches of a Service, 
between the Services, and between military and civilian 
organizations than did World War II. Such a complete 
organization should include a permanent operations 
analysis division to serve all branches concerned with 
operations. A single group to serve all forces is desir¬ 
able since close cooperation of the forces will probably 
be the future order. 

Strategic attack and defense in future wars will be 
entirely different from attack and defense in World 
War II and will overshadow tactical attack and de¬ 
fense in importance. The information that has been 
acquired on the effectiveness and use of weapons will 
be partly obsolete, but the need for such knowledge 
and for an adequate supply of men able to use it will 
be greater than before. The principles of terminal bal¬ 
listics and the effects of shock waves will not be 


changed; they must be thoroughly understood so that 
they may be used correctly in evaluating the perform¬ 
ance of new weapons. 

18.4.1 Peacetime Functions of Operations 

Analysis Divisions 

The peacetime functions of a permanent operations 
analysis division must include the following: 

1. The collection of information on the perform¬ 
ance of weapons as they are developed and the estima¬ 
tion of the performance of weapons as they are 
planned. 

2. The discovery of advantageous uses of existing 
weapons and recommendation of developments of new 
weapons. 

3. The evaluation of new weapons while still in the 
planning stage, as a guide to their best development. 

4. The procurement and training of suitable men 
for operations analysis in a future war, before the 
need for such men arises. 

5. The planning of field organizations and methods 
of operation in preparation for their need. 

18.4.2 Training of Future Operations 

Analysts 

The training of suitable men for work as operations 
analysts in weapon effectiveness and selection must be 
somewhat broader than it has been in the past, because 
the actual weapons of the future cannot be predicted 
very accurately and will certainly show greater variety 
than the weapons of World War II. Training should 
be as thorough as possible in the fundamentals of ap¬ 
plied physics and applied mathematics, including the 
fundamental principles of explosive effects and termi¬ 
nal ballistics. The subject matter of the present vol¬ 
ume, kept up to date, would be an excellent base for 
such broad training. 



Chapter 19 


WEAPON DATA SHEETS 


i9.i INTRODUCTION 

he chief functions of Division 2 have been to 
collect and organize information on the perform¬ 
ance of weapons and to supply this information to 
those needing it. Since it is obvious that the useful¬ 
ness of such information is always limited by the 
manner and extent of its distribution, considerable 
efforts have been made to make the distribution as 
effective as possible. 

The effective distribution of information on weapon 
performance is made difficult by the fact that such 
information is particularly useful to individuals who 
are in or very near the field; the wide dispersal and 
large numbers of prospective users of weapon data 
seriously limits the effectiveness of the usual methods 
of dissemination, such as personal contact and distri¬ 
bution of formal reports. The Weapon Data Sheets are 
designed to minimize this difficulty by putting weapon 
data in compact and accessible form suitable for wide 
distribution and immediate use. 

Material has been issued as a looseleaf notebook, 
entitled Weapon Data — Fire, Impact, Explosion (for¬ 
merly Effects of Impact and Explosion ). The looseleaf 
form was chosen so that available material could be 
issued at once and new sheets and revisions of old ones 
could be added as they became available. In general, 
each sheet deals with one aspect of weapon perform¬ 
ance, presenting the material in the form of a table, 
chart, or a combination of these. Incident Summaries 
have been included to give a detailed description of 
bomb damage to specific typical targets. 

1911 Distribution of the Report 

Two sizes of books were issued: a desk size and a 
pocket book. The first 50 copies of the desk-size loose¬ 
leaf notebook, containing 15 Weapon Data Sheets and 
6 Incident Summaries, were distributed in July 1943. 
Additional sheets have been prepared and old sheets 
revised as necessary, and the final edition of the book 
contains 81 Weapon Data Sheets and 17 Incident Sum¬ 
maries. The distribution list has grown rapidly. The 
total distribution, including the regular desk-size 
looseleaf notebook, the pocket edition for field use, 
and the bound final edition, reached nearly 1,200 


copies. In addition to this direct distribution by the 
Division, the Eighth Air Force reprinted more than 
600 copies of the early sheets for the use of ordnance 
officers, and later, U. S. Strategic and Tactical Air 
Forces requested 1,500 copies of each new sheet to con¬ 
tinue this distribution. In addition, several of the sheets 
have been reproduced in various reports and manuals 
of Division 2 and other organizations. 

1912 Final Edition of the Report 

The final edition of this notebook was issued as 
OSRD Report 6053, and more than 100 copies were 
bound and placed in permanent libraries. All sheets 
of the final edition, with one exception and a few 
minor corrections, are reprinted as part of this chapter 
to serve as reference material for other chapters of 
this report. 

19.2 MATERIAL INCLUDED IN THE 

NOTEBOOK 

The notebook was originally conceived as a collec- 

O %J 

tion of material useful to air force personnel and 
others concerned with the performance of bombs; 
hence all of the early sheets contain only data on the 
characteristics and performance of aerial bombs. The 
scope of the notebook was expanded later to include 
artillery weapons, demolition charges, and land mines, 
but the final edition still places the greatest emphasis 
on bombs. 

19,2,1 Choice of Subject Matter 

The choice of subject matter for the Weapon Data 
Sheets depended upon the importance of the subject 
and the availability of information. The ready avail¬ 
ability of personnel of the Princeton Universitv Sta- 
tion, Division 2, and of the Committee on Fortifica¬ 
tion Design [CFD] for consultation has resulted in 
a large proportion of sheets being on subjects with 
which the division and the committee were directly 
concerned. The extensive collection of British reports 
on bomb damage in the Division 2 library (see Chapter 
17) was used for preparation of the early sheets on 
damage to structures; additional sheets on this subject 
have been based on bomb damage surveys by the Army 



342 


RECOMMENDATIONS FOR FUTURE WORK 


343 


Air Forces Evaluation Boards in the Mediterranean, 
European and Southwest Pacific theaters, the U. S. 
Strategic Bombing Survey, the Bombing Analysis Unit 
(British), and similar groups. The close liaison be¬ 
tween Division 2 and various Service organizations 
such as the Office of the Chief of Engineers, the Ord¬ 
nance Department, and the Bureau of Ordnance has 
made much material available and thus influenced 
the choice of subject matter for Weapon Data Sheets. 

The sheets giving quantitative information on the 
effectiveness of weapons on specific types of targets 
are based on studies by the Weapon Effects Group of 
the Princeton University Station, Division 2, and the 
choice of subject matter was largely dictated by Service 
requests for target vulnerability studies. These studies 
were based on bomb-damage reports available in the 
Division 2 library and on reports from the various 
theaters, many of which were furnished by the Service 
organizations requesting the target studies. 

Much material prepared by contractors of Division 
2 other than the Princeton University Station and by 
other divisions of NDRC has been included in the 
notebook. The largest and most important single group 
of such sheets is the group of incendiary bomb sheets 
prepared by Section 11.3 of Division 11. 

1922 Sources of Information 

For each individual sheet an exhaustive survey of 
all available information was made, using the facilities 
of the Division 2 library (see Chapter 17), the advice 
of various Service liaison connections, and other sources 
described above. The results of the various British 
researches and reportings of bombing incidents have 
been made available through the cooperation of the 
Research and Experiments Department of the Min¬ 
istry of Home Security. 

Whenever possible, one or more experts on each sub¬ 
ject were consulted at the beginning of each study for 
advice on sources of information and again before 
printing the sheet for approval of what had been done. 

Sources of information for each of the Weapon Data 
Sheets are listed at the end of this chapter, after the 
sheets themselves. 

19.2.3 Presentation of Material 

The methods of presentation can best be understood 
by examination of the sheets making up the bulk of 
this chapter. Throughout, an effort has been made to 
present the material in a compact, immediately usable 
form. 


The various subjects treated have been arranged to 
keep sheets on similar subjects together. The arrange¬ 
ment of sections is as follows: 

1. Attacking Weapons 

1A Physical Characteristics 
IB Striking Velocity and Angle of Impact 
1C Aircraft Loading 

2. Impact 

2A Penetration 
2B Scabbing 
2C Perforation 

3. Explosion 

3A Air Blast 
3B Earth Shock 
3C Underwater 

4. Fire (no work done on this section) 

5. Fragmentation (no work done on this section) 

6. Target Vulnerability 

6A Components of Structures 
6B Industrial Buildings 
6C Special Industrial Targets 
6D Military Targets 
6E Utilities 
6F Transportation 

7. Bomb Performance 

APPENDIX 

0 Miscellaneous Information 

Incident Summaries 

193 RECOMMENDATIONS FOR 

FUTURE WORK 

The success of the looseleaf notebook form of data 
sheets warrants a continuation of the work, or at least 
a plan for having such material available for all who 
may need it at the beginning of any future war. The 
importance of having as much information as possible 
conveniently available at the beginning of a war is 
great; many users of the Weapon Data Sheets have 
expressed regret at receiving sheets only in the last 
half of World War II when they were sorely needed 
for guidance of new personnel in the early operations. 
All material issued in such a form should be subject 
to constant revision. A large part of the usefulness of 
such a notebook is in having a wide variety of useful 
information available in condensed form in one book, 
and this advantage is lost if the material is not kept 
up to date. 



344 


WEAPON DATA SHEETS 


19 31 Suggested Changes in the Present 

Notebook 

Not all Weapon Data Sheets that would be desirable 
in the notebook have been prepared. Sheets on charac¬ 
teristics of certain weapons such as rockets and artil¬ 
lery projectiles, information on terminal ballistics of 
materials such as brick, stone, and wood, and revision 
of several of the sheets on concrete perforation and 
armor perforation were planned but not executed 
before the end of World War IT. Other work that was 
planned but not completed concerned revision of pres¬ 
ent sheets and addition of several new sheets for Part 
3 on explosive effects. 

In the original plan of the notebook, Part 4 was to 
contain information of a fundamental nature on the 
effects of incendiaries, and Part 5 was to contain in¬ 
formation on fragmentation. A small amount of in¬ 
formation on these two subjects is included in Part 6, 
but no thorough studies of incendiary effects and frag- 
mentation have been included in the notebook. Any 
continuation of this work should certainly include de¬ 
tailed studies of these two important subjects. 

Part 6, dealing with target vulnerabilities, includes 
sheets based on studies made at the request of the Serv¬ 
ices. Any future work on a similar notebook or con- 
tinuation of the present notebook should include stud¬ 
ies of the physical vulnerabilities of a wider variety 
of targets, made along the lines suggested in Chap¬ 
ter 16. 

194 SOURCES OF INFORMATION FOR 
THE DATA SHEETS 

Each data sheet is based on the best information 
available to the Division at the time the sheet was pre¬ 
pared. The important sources are listed on each sheet, 
or are noted by a reference in the lower left corner of 
the sheet. The references AES, EWT, and OTB fol¬ 
lowed by numbers refer to the Division 2, NDRC, re¬ 
ports Air and Earth Shod’, Effects of T Vcapons on 
Targets, and Ordnance and Terminal Ballistics; the 
reference PTM refers to Princeton Technical Mem¬ 
oranda published by the Princeton University Station 
of Division 2, NDRC. The numbers following each of 
these references refer to a particular issue of the report. 
Some of these references are reports of original re¬ 
search. Others are studies of information from a num¬ 
ber of reports and include references to original 
sources. 

The most important sources of information for each 


sheet are listed below, with no attempt to list all 
sources. Some remarks on the method of analysis used, 
and anv information that might be useful in extra- 
polating the information to new weapons or in mak¬ 
ing further study of the subject are included. 

Explosives 

Sheet 1A1 summarizes the best available informa¬ 
tion on the properties and uses of currently used high- 
explosive [HE] fillings for bombs and demolition 
charges. Information from the following sources was 
used: 

1. Table of Military High Explosives, Explosives 
Research Memorandum No. 10 (first revision), Navy 
Department, Bureau of Ordnance. 

2. Introduction to Explosives, OSRD Report No. 
5401, Division 8, NDRC, August 1945. 

3. Report on HBX and Tritonal, OSRD Report No. 
5406, Committee on Fillings for Aerial Bombs, Divi¬ 
sions 2 and 8, NDRC, July 1945. 

4. Informal communication from Explosives Re¬ 
search Laboratory, Bruceton, Pa., Division 8, NDRC, 
July 1945. 

Physical Characteristics of Weapons 

Sheets 1A3, lA3a*, lA3b, lA3c, lA3d, lA4a, lA5a, 
lA5b, 1A6*, lA7a, lA7b, 1C1 are simple tabulations 
of the physical characteristics of weapons. Sheets giv¬ 
ing characteristics of United States weapons were sub¬ 
mitted to the relevant Service organizations before 
publication. Those listing characteristics of foreign 
weapons were checked by using several independent 
references where possible, and certainly are not com¬ 
plete. In using these sheets manufacturing tolerances 
must be allowed for and it must be remembered that 
total weights and weights of explosive fillings may 
vary by 5 per cent from the values given. The most 
important references for physical characteristics of 
weapons are listed below. 

5. Catalogue of Standard Ordnance Items, Tech¬ 
nical Division, Office of the Chief of Ordnance, U. S. 
Army. Continuing looseleaf publication, three vol¬ 
umes and Limited Procurement Supplement. 

6. Catalogue of Enemy Ordnance Material, Office 
of the Chief of Ordnance, U. S. Army. Continuing 
looseleaf publication. 

7. United States Bombs and Fuzes, British Bombs 
and Fuzes, Enemy Bombs and Fuzes, and similar pub¬ 
lications, United States Navy Bomb Disposal School, 
Washington. Additions and revisions issued fre¬ 
quently. 



SOURCES OF INFORMATION FOR THE DATA SHEETS 


345 


8. Advanced Fuze and Explosive Ordnance Bul¬ 
letin, United States Navy Bomb Disposal School, 
Washington. Published monthly. 

9. Intelligence Bulletin, United States Navy Bomb 
Disposal School, Washington. Biweekly publication. 

10. Bomb Disposal Technical Information, Army 
Service Forces, Ordnance Department, Ordnance 
Bomb Disposal Center, Aberdeen Proving Ground, 
Md. Semimonthly publication. 

11. Technical Manuals issued by the War Depart¬ 
ment. Manuals are published on a variety of subjects. 
Pertinent manuals were used for each sheet. 

12. Ordnance Pamphlets issued by the Bureau of 
Ordnance, U. S. Navy. Pamphlets are issued for vari¬ 
ous weapons. Pertinent pamphlets were consulted for 
each sheet. 

13. Engineer Intelligence Bulletins, Technical In¬ 
telligence Branch, Military Intelligence Division, Of¬ 
fice of the Chief of Engineers, Army Service Forces, 
U. S. Army. Several bulletins on mines and demoli¬ 
tion charges. Bulletin No. 3 and revisions tabulate 
dimensions of United States and foreign mines and 
demolition charges. 

Flight Data for Bombs 

Sheet 1B4 is based on calculations of the trajectory 
of bombs falling in a vacuum. These calculations 
neglecting air resistance are considered as accurate as 
more elaborate calculations for bombs dropped from 
altitudes below 5,000 ft. The equations used are given 
on the sheet. Sheets 1B5*-1B21 give striking veloc¬ 
ity and angle of impact for bombs as calculated using 
ballistic coefficients and condensed bombing tables 
furnished by the Ordnance Department, U. S. Army, 
and the Ballistic Research Laboratory, Aberdeen Prov¬ 
ing Ground, Md. The striking velocities were deter¬ 
mined by plotting the striking velocity as abscissa and 
the reciprocal of the ballistic coefficient for time of 
flight as ordinate, values being taken from condensed 
bombing tables. Separate graphs were made for each 
plane speed, and curves were drawn on the graphs for 
each altitude. Knowing the ballistic coefficient for time 
of flight of a given bomb as a function of altitude, a 
curve was drawn through the points determined by the 
reciprocal of the ballistic coefficient and the inter¬ 
section of this value with the corresponding line for 
each altitude. From this curve, plotted on each of 
the graphs described above, the striking velocity of 
the bomb dropped from any altitude at any horizontal 
plane speed could be determined. A similar method 
was used for determining the angle of impact, plotting 


the angle of fall as the abscissa and the reciprocal of 
the ballistic coefficient for range as ordinate, values 
being taken from condensed bombing tables. Separate 
graphs were made for each plane speed, and lines were 
drawn for each altitude. The procedure described above 
was followed to determine the angle of impact of the 
bomb for various combinations of altitude and plane 
speed, using the ballistic coefficient for range for each 
bomb. The results were used in drawing the sets of 
curves shown on the data sheets. The accuracy of 15 
per cent in striking velocity and 4 degrees in impact 
angle is due to inaccuracies in ballistic coefficients and 
not to inaccuracies in the method of presentation. 

Concrete Penetration, Scabbing, 
and Perforation 

Sheet 2A1 is a nomogram of the equation 


x 

d 


J + 282 S~* 


- j d 0 - 215 ( — 

<P ) V 1000 


3/2 


4 >( 0 ), 


where x is the penetration measured normal to the 
surface in inches, d is the projectile diameter in 
inches, S is the compressive strength of the concrete as 
measured by cylinders in pounds per square inch, w 
is the weight of the projectile in pounds, V is the 
striking velocity of the projectile in feet per second, 
and 6 is the striking obliquity measured from the 
normal. In constructing the nomogram a graphical 
function of the projectile diameter, which is very 
nearly d 0 - 215 , was used instead of d 0 - 215 given in the 
equation. A graphical function of the obliquity, based 
on averaged data for a large number of firings of pro¬ 
jectiles of various sizes and shapes was used for <f>(6). 

Sheet 2B1 is based on the nomogram of sheet 2A1 
and the relation s/d = 2.12 -f- 1.3 6x/d, where x/d 
is from the equation above, s is the thickness of target 
that can just be scabbed, and d is the projectile diam¬ 
eter; here s, x, and d are measured in the same units. 

Sheet 2C1 is based on the nomogram of sheet 2A1 
and the relation e/d = 1.32 -f- 1.24a: /d, where x/d 
is from the equation for sheet 2A1, e is the thickness 
of target that can be perforated, d is the projectile 
diameter, and e, x, and d are all measured in the same 
units. 

The equations are empirical relations based on 
analysis of approximately 600 rounds fired in tests 
of 37-mm, 75-mm, 3-in., 155-mm, 12-in., and 16-in. 
armor-piercing [AP] projectiles, and about 75 rounds 
of inert bombs dropped on reinforced-concrete tar¬ 
gets. Data are from the following sources: 

14. Penetration and Explosion Tests on Concrete 







346 


WEAPON DATA SHEETS 


Slabs. Report 1: Data, Interim Report No. 20 of the 
Committee on Passive Protection Against Bombing. 
National Research Council, January 1943. 

15. Armor-Piercing Projectile Tests on Concrete 
Slabs, San Francisco District U. S. Engineer Office 
at the direction of the Chief of Engineers, U. S. Army, 
May 1942. 

16. Report of Bomb Tests on Materials and Struc¬ 
tures, Passive Defense Bulletin No. 1, War Depart¬ 
ment, Office of the Chief of Engineers, September 
1941. 

17. Armor-Piercing Bomb Test, Protection Tests, 
Bulletin No. 3, War Department, Office of the Chief 
of Engineers, 1941. 

18. Report of Bomb Tests on Burster Slabs, Sec¬ 
ond Series, Passive Protection Bulletin No. 8, War 
Department, Office of the Chief of Engineers, Feb¬ 
ruary 1943. 

Since these sheets were published, new data have 
been obtained and a revision of the sheets is desirable. 
Analysis of recent data indicates that the relations 
used in sheets 2B1 and 2C1 for scabbing and per¬ 
foration should be s/d — 2.28 -f- lA3x/d and e/d 
— 1.23 -f- 1.07 x/d instead of the equations given 
above. Data also show that the dependence of pene¬ 
tration on the strength of the concrete is not so sim¬ 
ple as given by the equation above, that the size of 
the aggregate has a small but definite effect on pene¬ 
tration, that the effect of nose shape of the projectile 
on penetration is greater and more complicated than 
indicated by the correction factor of V 2 used in the 
penetration equation, and that if a larger factor is 
used for nose effect the exponent of velocity in the 
empirical equation is greater than %. Progress has 
been made towards a theory of penetration to replace 
the empirical interpolation formulas used for the 
nomograms but this has not reached a satisfactory 
stage at present. The following references contain 
new material on terminal ballistics of concrete: 

19. Effect of Concrete Properties on Penetration 
Resistance, Interim Report No. 27 of the Committee 
on Fortification Design, National Research Council, 
July 1944. 

20. Ballistic Tests on Concrete Slabs, Interim Re¬ 
port No. 28 of the Committee on Fortification Design, 
National Research Council, July 1944. 

21. Penetration Theory: Separable Force Laws 
and the Time of Penetration, NDRC Report No. 
A-333; OSRD Report No. 5258, Division 2, NDRC. 
June 1945. 


Sheet 2Cla is based on calculations from sheet 
2C1, with some corrections using data described in 
the preceding paragraph. Striking velocities and ob¬ 
liquities were obtained from sheets 1B5*-1B10*. 
The data on penetration in soil is included for com¬ 
parison purposes and is taken directly from sheets 
2A2* and 2A2a. The data on bomb case breakup was 
taken from reference 22. The values for perforation 
of combination targets of soil and concrete were 
computed by the method described in reference 23, 
based on small-scale test data. The information on 
bomb case breakup and on perforation of composite 
targets is limited, so that the values given on the 
sheet should be treated as approximations. 

22. Ballistic Data — Performance of Ammunition, 
Technical Manual TM 9-1907, War Department, 
1945. 

23. Composite Slabs. Interim Memorandum No. 
M-13 of the Committee on Fortification Design, Na¬ 
tional Research Council, July 1945. 

The crater profiles shown in sheet 2A3 are copied 
directly from the following report: 

24. Penetration and Explosion Tests on Concrete 
Slabs. Report II: Crater Profiles. Interim Report 
No. 21 of the Committee on Passive Protection 
Against Bombing, National Research Council, Janu- 
arv 1943. 

Soil Penetration 

These sheets are based on analysis of penetration 
tests using small-caliber projectiles, and penetration 
data for inert bombs dropped on various soils. The 
graphs in sheet 2A2* are based on an empirical re¬ 
lation between the caliber penetration, x/d, and the 
striking velocity, where x is the penetration measured 
along the path of the missile and d is the diameter of 
the missile, both measured in the same units. It was 
found that for projectiles having different caliber 
densities (weight/diameter 3 ) the caliber penetration 
at a given velocity was very nearly proportional to 
the cube root of the caliber density for a range of 
caliber density from 0.15 to 0.65 lb per cu in. Thus 
penetration is approximately proportional to the cube 
root of the projectile weight, as shown on the sheet. 
The figures given for the relation between the depth 
below the surface and the length of the curved un¬ 
derground trajectory are based on a small number 
of measurements of actual bomb penetrations and a 
large number of measurements of penetration of 
small-caliber bullets. These figures are used in sheet 
2A2a, and are not of great accuracy. Changing these 



SOURCES OF INFORMATION FOR THE DATA SHEETS 


347 


figures by 25 per cent lias small effect on the penetra¬ 
tion values given in sheet 2A2a. Sheet 2A2a is based 
on sheet 2A2*, using striking velocities from various 
altitudes as in sheets 1B5*-1B9*. The data and 
analysis for both sheets are given in the following 
reference: 

25. Penetration in Soils, Interim Report No. 30 
of the Committee on Fortification Design, National 
Research Council, July 1944. 

Ricochet 

Sheet 2A5 is based on data for small-caliber pro¬ 
jectiles, medium and large artillery shells, and bombs 
dropped from low altitude. Using the impact angle 
and striking velocity as variables, a graph was made 
by plotting each round fired, with indication to show 
whether ricochet did or did not occur. It was found 
that a band could be drawn separating the regions 
of ricochet and no ricochet for each material. The 
data are for ricochet or no ricochet from thick tar¬ 
gets. Ricochet from steel is not treated, since the 
limit is between ricochet and perforation instead of 
between ricochet and penetration, and is therefore 
different for every plate thickness. Most of the rico- 
ohet data are from the following sources: 

26. Pico diet Off Land Surfaces, BRL Report No. 
535, Ballistic Research Laboratory, Aberdeen Prov¬ 
ing Ground, Md. 

27. Ricochet of Bombs Off Various Surfaces When 
Released at 300 Miles per Hour, BRL Report No. 256, 
Ballistic Research Laboratory, Aberdeen Proving 
Ground, Md. 

28. The Ricochet of Bombs — Targets on Water, 
Service Branch, Technical Division, Office of the Chief 
of Ordnance, War Department. 

29. The Connexion between Striking Velocity and 
Ricochet Angle at Low Striking Velocities, Twenty- 
fifth Interim Report on Concrete for Defence Works, 
Road Research Laboratory, Ministry of Supply (Brit¬ 
ish). Note No. MOS/433/ACW. 

30. Ballistic Tests on Concrete Slabs, II: Effect 
of Nose Shape, NDRC Report No. A-388, OSRD Re¬ 
port No. 6459, Division 2, NDRC. 

See also references 14, 20, and 24. 

Plastic Protection 

Sheet 2C2 is based on British and American data 
on the performance of plastic armor in stopping 
small-caliber bullets. These data were used to deter¬ 
mine the thickness plastic protection required for 
““adequate protection” (5 per cent or less of the bul¬ 


lets perforating). Most of the data came from the 
following report: 

31. On the Probability of Perforation of Plastic 
Protection by Caliber .30 AP M-2 Bullets, NDRC 
Report No. A-246, OSRD Report No. 3231, Division 
2, NDRC, February 1944. 

Armor Perforation; Mild Steel Perforation 

Sheets 2C3, 2C3a, 2C4, 2C5*, 2C5a, 2C6, 2C7, 
and 2C8 are based on empirical relations between the 
scaled variables e/d and ( w/d 3 ) V 2 , where e is the 
thickness of plate perforated in inches, d is the diam¬ 
eter of the projectile in inches, w is the weight of 
the projectile in pounds, and F is the striking velocity 
of the projectile in fps. For small-caliber jacketed 
bullets, projectiles with cap or windshield which come 
off on impact, or tungsten-carbide cored projectiles, 
w and d are the weight and diameter of the core, or 
part of the projectile which penetrates the plate. An 
attempt was made to find an empirical equation re¬ 
lating the variables, but the results were unsatisfac¬ 
tory. The sheets show the experimental data in the 
form of bands which include most of the data for 
projectiles perforating without shatter of the missile. 
The curves for individual weapons, given in sheets 
2C3a and 2C5a, end at the combination of plate 
thickness, striking velocity, and obliquity at which 
shatter or body breakup begins. The other sheets are 
averages of a large quantity of data for various pro¬ 
jectiles and bombs, and the shatter limit is obscured 
by the method of presentation. The references for all 
sheets are listed below. References 32-35 are for sheet 
2C3; reference 36 is for sheet 2C3a; references 37 
and 38 are for sheet 2C4; references 39 and 40 are 
for sheet 2C5*; sheet 2C5a is based on an earlier edi¬ 
tion of reference 40 and should be revised; refer¬ 
ences 41-46 are for sheet 2C6; references 47 and 
48 are for sheet 2C7; references 49 and 50 are for 
sheet 2C8. 

32. Mechanism of Armor Perforation — 2nd Par¬ 
tial Report, Watertown Arsenal Report 710/492, May 
1943. 

33. Penetration of Homogeneous Armor by Un¬ 
capped Projectiles at 0° Obliquity, Naval Proving 
Ground Report 1-43, U. S. Naval Proving Ground, 
Dahlgren, Va., April 1943. 

34. Armor Penetration Data, Armor Penetration 
Graphs. Canadian Military Headquarters, Depart¬ 
ment of National Defense, 1943. 

35. Ballistic Tests of STS Armor Plate Using 
37-man Projectiles, NDRC Report No. A-156, Ballis- 




348 


WEAPON DATA SHEETS 


tic Research Group, Princeton University Station, 
Division 2, NDRC, March 1943. 

36. Armor Perforation Curves, Ballistic Section, 
Technical Division, Office of the Chief of Ordnance, 
U. S. Army. Most of these curves are also published 
in reference 22. 

37. Armor-Piercing Bullet Cores, Watertown Ar¬ 
senal Report No. 762/203, May 1943. 

38. Seventh Partial Report on Light Armor Inves¬ 
tigation, and Eighth Partial Report on Light Armor, 
Naval Research Laboratory Reports No. 0-1600 and 
0-1745, U. S. Naval Research Laboratory. 

39. Compilation of Data Resulting from Trials to 
Determine the Explosive Effects of Aircraft Bombs 
and Means of Protection Therefrom, Research Depart¬ 
ment, Woolwich, England, October 1938. 

40. Armor Perforation by Service Bombs, BuOrd 
Sketch No. 124400, Rev. B., U. S. Navy Department, 
Bureau of Ordnance, 1944. 

41. High-Velocity Armor-Piercing Ammunition, 
Ordnance Department, U. S. Army, August 1944. 

42. High-Velocity Development, Ordnance Depart¬ 
ment, U. S. Army, October 1943. 

43. Proving Center Firing Record P-3310J,\, Ord¬ 
nance Program 5962, Aberdeen Proving Ground, Md. 

44. S. D. Technical Artillery Report No. 21, Ca¬ 
nadian Military Headquarters, June 1943. 

45. Trials Carried out in Connection with A.T.D.B. 
Projects Number 6 and 7, Army Technical Develop¬ 
ment Board, Canada, 1944. 

46. Ordnance Board Proceedings (British), Nos. 
Q95, Q1471, Q1546, Q1716, Q1834, Q1838, Q1953, 
Q2521, 25242. 

47. Tactical and Technical Trends, No. 17, Mil¬ 
itary Intelligence Division, War Department, Wash¬ 
ington, January 1943. 

48. Ordnance Board Proceedings (British), Nos. 
Q1834, 26433. 

49. Second Partial Report on Light Armor Inves¬ 
tigation, Naval Research Laboratory Report No. 
0-1429, U. S. Naval Research Laboratory, March 1940. 

50. The Ballistic Properties of Mild Steel, NDRC 
Report No. A-lll, Ballistic Research Group, Prince¬ 
ton University Station, Division 2, NDRC. 

Air Blast 

Sheets 3A1, 3A2*, and 3A2a are based on analysis 
of a large quantity of data from various tests of ex¬ 
plosives. Individual sets of data were taken from a 
number of references, and the separate references are 


not listed here. All data for pressure or impulse were 
averaged for the sheets. The data for pressure were 
compared by relating the pressure P in psi to the scaled 
distance from the charge r/wd, where r is the distance 
in feet and w is the charge weight in pounds. The 
data for impulse were compared by relating the scaled 
impulse I/w* to the scaled distance from the charge 
r/w*, I being the impulse in pound-milliseconds per 
square inch and the other variables as above. The 
effects of different types of explosive were taken into 
account by means of multiplicative factors, based on 
equivalent weight of explosive. The effect of the bomb 
case on impulse is described in sheet 3A2a and in ref¬ 
erence 52 below. The effect of the bomb case on peak 
pressure has not been determined. 

Sheet 3A1 is a nomogram of the equation 

P = 412 (hr 3 — 105z~ 2 + 39. 5z~\ 

where P is the pressure in psi and z = r/w*, r being 
the distance from the explosion in feet and w being 
the weight of explosive in pounds. This equation is 
based on averaging a large number of pressure meas¬ 
urements, all made prior to June 1943, on bombs 
filled with various explosives and detonated on the 
ground. When this is compared to recent pressure-dis¬ 
tance curves obtained from explosion of small bare 
TNT charges in the air it is found to predict pressures 
which are lower than those that would be expected if 
ground detonation is taken into account by replacing 
the weight of charge by twice the weight used for the 
free air curve. The amount by which the nomogram 
is lower than the values predicted from the free air 
curve varies with the distance from the bomb from 
50 per cent at z = 10 to 3 per cent at z = 30. 
In view of the fact that the peak pressure is different 
for different explosives and that there may be an effect 
of the bomb case thickness on pressure, the difference 
in shape or the pressure-distance curve given by the 
nomogram and the pressure-distance curve given by 
the bare TNT charges is not unexpected, since the 
nomogram is based on simple averaging of measure¬ 
ments involving various types of explosive in cases of 
various thickness. 

A pressure-distance curve for bare TNT charges is 
given in the upper figure of sheet 3A9. 

Experiments using small bare charges of various 
explosives indicate that the pressures due to detona¬ 
tion of equal weights of various explosives have the 
following relative values: torpex 2, 1.15; HBX, 1.13; 
minol 2, 1.09; Composition B (RDX/TNT 60/40), 
1.08; tritonal, 1.07; TNT, 1.00 ; amatol (50/50). 0.93. 



SOURCES OF INFORMATION FOR THE DATA SHEETS 


349 


Sheet 3A2* and sheet 3A2a are based on the equa¬ 
tions given on the sheets. The equations are based on 
averaging a large quantity of data for charges deto¬ 
nated on the ground. The effect of explosive type on 
impulse and on pressure, the dependence of pressure 
and impulse on distance, and the effect of the bomb 
case on impulse are discussed in the following papers. 

51. Small Charge Air Blast Experiments, NDRC 
Report No. A-191, OSRD No. 1518, Division 2, 
NDRC, June 1943. 

52. Dependence of Positive Impulse of Blast on 
Charge-Weight Patio, AES-4, OSRD No. 4356, Air 
and Earth Shock, Yol. 4. p. 43, Division 2, NDRC, 
November 1944. 

53. Relation between Positive Blast Impulse and 
Charge-Weight Ratio for Bombs, AES-4, OSRD No. 
4356, Air and Earth Shock, Yol. 4, p. 51, Division 2, 
NDRC, November 1944. 

54. Order of Effectiveness of Explosives, IV, 
AES-6, OSRD No. 4649, Air and Earth Shock, Yol. 
6, p. 1, Division 2, NDRC, January 1945. 

55. The Air Blast Performance of Some High Ex¬ 
plosives, AES-7, OSRD No. 4754, Air and Earth 
Shock, Yol. 7, p. 9, Division 2, NDRC, February 1945. 

Sheet 3A3 gives a curve for the relation between 
side-on and face-on blast pressures in air. This curve 
is calculated from the requirement that the velocity 
imparted to the gas particles by the oncoming wave is 
just cancelled by the velocity imparted by the reflected 
wave. The value of these velocities may be found from 
the Rankine-Hugoniot equations, which give, among 
other things, particle velocities as a function of pres¬ 
sure. (See for instance, Aerodynamic Theory, edited by 
W. F. Durand. Division H by G. I. Taylor and J. W. 
Maccoll. J. Springer, Berlin. 1935.) 

Contact Explosions 

Sheet 3A4 was prepared directly from reference 56, 
which describes measurements of the impulse due to 
explosion of small charges of various shapes in contact 
with an impulse pendulum. 

56. Impulse Delivered to a Plane Slab by a Contact 
Explosion, II, AES-13d, OSRD No. 5506d, Air and 
Earth Shock, Yol. 13, p. 41, Division 2, NDRC, 
August 1945. 

Cone End Charges 

Sheet 3A5 was prepared on the basis of the available 
experimental data on penetration and perforation of 
reinforced-concrete slabs by cone end hollow charges 
detonated under controlled conditions. An attempt to 


correlate the data was made by plotting the depth of 
penetration as a function of the weight of explosive 
used, on log-log paper as shown on the sheet. The 
straight line giving a best fit to the data, as determined 
by the method of least squares, has a slope of 0.43. 
The large scatter in the data is such that this is not 
significantly different from the value of Vs for the slope, 
given by model laws. An attempt to reduce the scatter 
in the data by finding correlations with other variables 
such as type of explosive, thickness and material of 
cone liner, and cone angle failed. References used 
include: 

57. Shaped Charges for the Perforation of Concrete r 
Eastern Laboratory, Explosives Department, E. I. 
duPont de Nemours & Co., Inc., Gibbstown, N. J., 
May 1943. 

58. Theory and Application of the Cavity Effect, 
Report for November 1943, E. I. duPont de Nemours 
& Co., Inc., December 1943. 

59. Sixth Interim Report on Demolition of German 
Pillboxes, Road Research Laboratory, Ministry of 
Supply (British), April 1942. 

60. Fourth and Final Report on Demolition Tests 
on Concrete Bridge Piers, Road Research Laboratory, 
Ministry of Supply (British), August 1942. 

Sheet 3A6 is based on reference 61. The sheet is 
essentially an abstract of the reference. 

61. Performance of Hollow-Charge Weapons, OTB- 
12f, OSRD No. 5350f, Ordnance and Terminal Ballis¬ 
tics, A 7 ol. 12, Division 2, NDRC, July 1945. 

Effect of Air Burst on Blast 

Sheets 3A 7, 3A8, and 3A9 are based on experimen¬ 
tal studies of small bare charges and of bombs deto¬ 
nated at various heights above ground. The sheets are 
based on the following references. Some of the graphs 
given in the sheets are based on new adjustments of 
data given in the references. 

62. The Effect of Air Burst on the Blast from 
Bombs and Small Charges: I. Experimental Results , 
OSRD Report No. 4246, Underwater Explosives Re¬ 
search Laboratory, Woods Hole, Mass., with collabora¬ 
tion from Stanolind Oil and Gas Company, Tulsa, 
Okla., Division 8, NDRC, October 1944. 

63. The Effect of Air Burst on the Blast from 
Bombs and Small Charges: II. Analysis of Experi¬ 
mental Results, NDRC Report No. A-320, OSRD No. 
4899, Division 2, NDRC, April 1945. 

64. Air Burst for Blast Bombs, NDRC Report No. 
A-322, OSRD No. 4943, Division 2, NDRC, April 
1945. 





WEAPON DATA SHEETS 


350 

65. The Effect of Height of Burst on the Blast 
Characteristics from 67-lb Bare Cylindrical Charges 
of BDX/TNT 60/40, ARD Explosives Report 16/45, 
Armament Research Department, Ministry of Supply 
(British), February 1945. 

66. Peak Pressure Dependence on Height of Deto¬ 
nation, AES-1, OSRD No. 4076, Air and Earth 
Shock, Yol. 1, p. 1, Division 2, NDRC, August 1944. 

67. Impulse Dependence on Height of Detonation, 
AES-2, OSRD No. 4147, Air and Earth Shock, Yol. 
2, p. 17, Division 2, NDRC, September 1944. 

68. Mach Deflection of Shock Waves from Charges 
Detonated in Air, AES-3, OSRD No. 4257, Air and 
Earth Shock, Yol. 3, p. 17, Division 2, NDRC, Oc¬ 
tober 1944. 

69. The Effect of Height of Detonation on Peak 
Pressure and Positive Impulse Measured Close to the 
Ground, xAES-5, OSRD No. 4514, Air and Earth 
Shock, Yol. 5, p. 49, Division 2, NDRC, December 
1944. 

70. Dependence of Optimum Impulse on Height of 
Gauge in Air Burst, AES-9c, OSRD No. 5011c, Air 
and Earth Shock, Yol. 9, p. 17, Division 2, NDRC, 
April 1945. 

Underground Explosions 

Sheet 3Bla* is based on analysis of a large amount 
of data for craters formed in various soils by explo¬ 
sive charges ranging from a fraction of a pound to 
more than 3,000 lb. The variables used in plotting the 
data were suggested by model theory. Separate graphs 
were made for each soil, and although there was a 
large scatter in the data a smooth curve was drawn 
for each set of data. The final curves are shown on 
sheet 3Bla*. Data were taken from a large number of 
reports, and most of the measurements are of individ¬ 
ual craters made in tests for purposes other than the 
study of cratering. Since most of the sources list only 
a few craters, individual references are not listed here. 
Reference 71 describes extensive tests of cratering by 
100- and 1,000-lb general-purpose [CP] bombs. The 
other references describe tests made with small charges 
to determine the effect of different types of explosive 
and the effect of charge shape on crater dimensions. 

71. Supplementary Test of Selection of Bombs and 
Fuzes for Bombardment Targets, AAF Proving 
Ground Command, Project No. 4249C471.6, the 
Army Air Forces Board, December 1944. 

72. Effect of Charge Shape and Orientation on 
Cratering in Soil, AES-3, OSRD No. 4257, Air and 


Earth Shock, Yol. 3, p. 1, Division 2, NDRC, Oc¬ 
tober 1944. 

73. Weight of Material Required to Fill Bomb 
Craters (Model Experiments ), BRL Report No. 488, 
Ballistic Research Laboratory, Aberdeen Proving 
Ground, Md., September 1944. 

74. The Comparative Performance of Various 
Bomb Fillings—Crater and Earthshock Effects. Part 
I, REN 452, Research and Experiments Department, 
Ministry of Home Security (British). 

75. The Order of Effectiveness of Various Explo¬ 
sives in Earth, AES-13b, OSRD No. 5506b, Air and 
Earth Shock, Yol. 13, p. 13, Division 2, NDRC, 
August 1945. 

Sheet 3Bib gives diameter of craters formed by 
detonation of line charges on the surface of the ground. 
Data from a number of tests were correlated by means 
of the scale factor w* suggested by model theory. The 
analysis, data, and sources of data are given in ref¬ 
erence 76. 

76. Cratenng by Line Charges, AES-13a, OSRD 
No. 5506a, Air and Earth Shock, Yol. 13, pp. 1, Divi¬ 
sion 2, NDRC, August 1945. 

Sheet 3B2 gives earth displacements due to under¬ 
ground explosions, based on analysis of a large num¬ 
ber of tests on bombs and bare charges. The data were 
plotted in terms of the model-law variables u/w* and 
r/w* where u is the displacement, r is the horizontal 
distance from the explosion, and w is the weight of 
explosive. Separate curves were obtained for the maxi¬ 
mum transient horizontal, maximum transient ver¬ 
tical, permanent horizontal, and permanent vertical 
displacements. The permanent displacements were de¬ 
termined by measuring the displacement of stakes in 
the ground. The transient displacements were meas¬ 
ured by photographing the motion of a lamp fastened 
to a stake, or by using an inertia trolley. Data for 
charges at small depths showed appreciable departure 
from the other values, and data for detonations in 
chalk gave smaller displacements than those observed 
in clay soil. Only the data for charges buried deeper 
than in clay soil were used. The data came from 
the following sources: 

77. Earth Movements Due to Explosions, Data 
Compilation No. 14, Research and Experiments 
Branch, Ministry of Home Security (British), Feb¬ 
ruary 1940. 

78. Earth Movement Due to 50-kg Bombs Exploded 
in Clay Soil at Richmond Park, RC 328, Road Re¬ 
search Laboratory Report to the Ministry of Home 
Security (British), May 1942. 



SOURCES OF INFORMATION FOR THE DATA SHEETS 


351 


79. Earth Movements in Different Directions Due 
to Explosion of Buried 50-kg Bombs in Clay Soil, EC 
314, Road Research Laboratory Report to the Min¬ 
istry of Home Security (British), February 1942. 

80. Earth Movements Due to German Bombs Ex¬ 
ploded Below Ground, RC 259, Road Research Labo¬ 
ratory Report to the Ministry of Home Security (Brit¬ 
ish), August 1941. 

81. Earth Movement Due to German and Bntish 
Bombs Exploded Below Ground, RC 153, Road Re¬ 
search Laboratory Report to the Ministry of Home 
Security (British), November 1940. 

82. Earth Movements Due to 250-kg Bombs Ex¬ 
ploded in Clay Soil, RC 312, Road Research Labora¬ 
tory Report to the Ministry of Home Security (Brit¬ 
ish), February 1942. 

83. Earth Movement Due to German 250-kg Bombs 
Exploded Below Ground in Chalk Soil, RC 313, 
Road Research Laboratory Report to the Ministry 
of Home Security (British), February 1942. 

84. Earth Movements Due to Buried Standard 
Charges, RC 416, Road Research Laboratory Report 
to the Ministry of Supply (British), November 1943. 

Sheet 3B3* gives nomograms for the pressure and 
impulse underground due to explosions underground. 
The nomograms are based on extensive tests of under¬ 
ground explosions described in reference 85. A 7 alues 
of the soil constants are from reference 86. Factors 
for pressure and impulse due to explosives other than 
TNT are from reference 87. A recent series of tests on 
the pressure and impulse at different depths due to ex¬ 
plosions at various depths is described in reference 88. 

85. Effects of Underground Explosions (in three 
volumes), Interim Report No. 26, Committee on For¬ 
tification Design, National Research Council, June 
1944. 

86. The Seismic Method of Explorations Applied 
to Construction Projects, Military Engineer, Septem- 
ber-October 1939. 

87. The Order of Effectiveness of Various Explo¬ 
sives in Earth, AES-13b, OSRD No. 5506b, Air and 
Earth Shock, Yol. 13, p. 13, Division 2, NDRC, 
August 1945. 

88. Final Report on Effects of Underground Ex¬ 
plosives, C. W. Lampson, OSRD No. 6645, NDRC 
Report No. A 479, submitted on February 20, 1946, 
and approved March 1946. 

Underwater Explosions 

The nomogram given on sheet 3C1 is taken directly 
from reference 89. Data sheet 3C2 was prepared from 


material in references 90 and 91, as described on the 
sheet. 

89. Underwater Explosives and Explosions, Re¬ 
port UE-16, p. 3, Division 8, NDRC, December 
1943. 

90. Theory of the Pulsations of the Gas Bubble 
Produced by an Underwater Explosion, Report No. 
C4-sr20-010, Columbia University, Division of Na¬ 
tional Defense Research, New London, Conn., Octo¬ 
ber 1941. 

91. On the Best Location of a Mine Near the Sea 
Bed, AMP Report 37.1R, Applied Mathematics 
Group, New York University; Applied Mathematics 
Panel, NDRC, May 1944. 

Impulse Criterion—Damage Levels 

The method of analysis used in arriving at the con¬ 
clusions given in sheet 6A0 is described in the sheet. 
The sheet is based on the references listed below. A 
discussion of the impulse criterion may be found in 
pages 17-24 of reference 64. 

92. House Damage by HE Weapons Acting by 
Blast, REN 214 Revised, Research and Experiments 
Department, Ministry of Home Security (British), 
March 1944. 

93. A Modification of the Impulse Criterion for 
Blast Damage, RC 349, Research and Experiments 
Department, Ministry of Home Security (British), 
September 1942. 

Vulnerability of Components of Structures 

Sheet 6Ala* and 6Alb* are based on analysis of 
column damage taken from reports of building dam¬ 
age. The data for various incidents were correlated by 
plotting the scaled distance from the explosion as 
abscissa and the index of column slenderness and 
aspect as ordinate and separating the plotted values 
corresponding to different degrees of damage, as 
shown on the sheet. The index of slenderness and as¬ 
pect is defined as the area of cross section of the col¬ 
umn material divided by the free area of the column 
exposed directly to the blast. This definition is sug¬ 
gested by a semiquantitative theory which ascribes 
the damage to air-blast impulse, with the blast wave 
assumed to act for the length of time required for 
the diffracted wave to make its way around the col¬ 
umn. Data are from the following references: 

94. Effect of German RE Bombs on Industrial 
Structures, REN 224, Ministry of Home Security 
(British), May 1943. 

95. Damage to Single Story Buildings, R.E. 4, 





352 


WEAPON DATA SHEETS 


Data Compilation No. 2, Ministry of Home Security 
(British), May 1942. 

96. Air Raid Damage Report — Dolphin Court 
Flats, Ministry of Home Security (British), Novem¬ 
ber 1940. 

97. Air Raid Damage Report, Serial No. Clf, Min¬ 
istry of Home Security (British), 1942. 

98. Blast Effect of Bomb on Steelwork, R.E. 4, 
Data Compilation No. 27, Ministry of Home Security 
(British). 

99. Damage to R. C. Framed Buildings, Data Com¬ 
pilation No. 32, Ministry of Home Security (Brit¬ 
ish), February 1942. 

Sheet 6A2 is based on examination of data on bomb 
damage to British buildings. The data show a rough 
correlation between the area of concrete floor slab 
removed and the location and size of the bomb. For a 
given bomb size it was found possible to make sepa¬ 
rate analyses of the data for area of floor destroyed 
for the floors adjacent to the bomb, the floor next 
above or below the bomb, and the third floor above or 
below the bomb. The separate curves are shown on 
the sheet. The curve labeled total area, all floors is 
twice the sum of the area given by the three curves 
for individual floors. A recent analysis, made since 
publication of the sheet, shows that although the three 
lower curves represent the data very well, the damage 
is not always symmetrical above and below the bomb, 
and the curve for the total area of all floors does not 
fit all incidents. This later analysis indicates that a 
better approach to the problem might be made by cor¬ 
relating the volume made unusable with the weight 
of explosive. If the volume destroyed is determined as 
the height of each story multiplied by the area of de¬ 
struction of the floor immediately above or below, 
whichever is greater, these separate volumes being 
summed for the entire building, then the relation 

V = 140 w fits the data very well, where V is the volume 
destroyed and w is the weight of explosive in the 
bomb. For American GP bombs this relation becomes 

V = 701F, where W is the weight of the bomb. Data 
on destruction of floor slabs by HE bombs may be 
found in the following references: 

100. Air Raid Damage Report, Serial No. Ai 
Ministry of Home Security (British), February 1943. 

101. Air Raid Damage Report, Serial No. Cl, 
Ministry of Home Security (British), February 1943. 

102. Air Raid Damage Report, Serial No. C2, 
Ministry of Home Security (British), February 1943. 

103. Air Raid Damage Report, Serial No. D4, 
Ministry of Home Security (British), February 1943. 


104. Damage to Steel Framed Buildings, R.E. 4, 
Data Compilation No. 26, Ministry of Home Security 
(British), February 1943. 

105. Model (Vs scale) and Full-Scale Tests of 
Resistance of Reinforced Concrete to Attack by Bombs 
Nearby and in Contact, RC 358, Road Research Lab¬ 
oratory Report to the Ministry of Home Security 
(British), September 1942. 

106. Interim Report of a Portion of Bomb Tests 
Conducted by the Ordnance Department on the Rein¬ 
forced Concrete Test Structure at Area H, Gunpow¬ 
der Neck, Aberdeen Proving Ground, Aid., Corps of 
Engineers, U. S. Army, December 1942. 

See also references 96, 97, and 99. 

Sheet 6A3* is based on analysis of available in¬ 
cidents of explosions inside and outside steel framed 
factory-type buildings. The maximum radius of re¬ 
moval off roofing was plotted as a function of the weight 
of explosive in the bomb for both asbestos cement and 
sheet steel roofing. It was found possible to draw 
separate curves for internal and external explosion 
for each type of roofing, as shown on the sheet. The 
second graph on the sheet is a more detailed study 
of the effect of a German 50-kg SC bomb on the 
roofs of buildings of different size. Data were from 
the following sources: 

107. Damage to Light Roofing and Walling Mate¬ 
rials, R.E. 4, Data Compilation No. 8, Ministry of 
Home Security (British), May 1943. 

108. Damage to Walls, R.E. 4, Data Compilation 
No. 10, Ministry of Home Security (British), May 
1943. 

109. Variations in the Behavior of Factory Roof 
Sheetings Subject to Blast, REN 220, Research and 
Experiments Department, Ministry of Home Security 
(British), May 1943. 

Sheets 6A5* and 6A6* are based on references 110 
and 111 respectively. These describe the methods of 
analysis and give references to original sources: 

110. Damage to Underground Reinforced Concrete 
Walls, EWT-5g, OSRD No. 5405g, Effects of Weap¬ 
ons on Targets, Yol. 5, NDRC, August 1945. 

111. Damage to Reinforced Concrete Wall Panels 
by Detonation of Contact and Remote Charges, EWT- 
3h, OSRD No. 5176h, Effects of Weapons on Tar¬ 
gets, Yol. 3. NDRC, June 1945. 

Target Vulnerability 

The sheets in sections 6B through 6F are studies 
of the physical vulnerability of various target types. 
All of these sheets except numbers 6D2 and 6E1 are 
based on source material and methods of analysis de- 



SOURCES OF INFORMATION FOR THE DATA SHEETS 


353 


scribed in various articles published m the NDRC 
report Effects of Weapons on Targets . Sheet GDI is 
based on a study of references listed on the sheet. 
Sheet 6E1 is based on a study of references 123 and 
124 listed below. The separate references for each 
sheet in this group are listed below in the order in 
which the sheets appear in the book. Sheet numbers 
are given immediately after the reference number. 

112. 6B1 Direct-TIit Effects of U.S. 500-lb GP 
Bombs on European Industrial Buildings: HE Struc¬ 
tural Damage, EWT-2f, OSRD No. 5045f, Effects of 
Weapons on Targets, Yol. 2, NDRC, May 1945. 

113. 6B1 Incendiary Effects of U. S. 500-lb GP 
Bombs on European Industrial Buildings: Probability 
of Initiation of Destructive Fires, EWT-3b, OSRD 
No. 5176b, Effects of Weapons on Targets, Vol. 3, 
NDRC, June 1945. 

114. 6B1 Spread of Fire within Single-Story Euro¬ 
pean Industrail Fire Divisions, Mixed HE-IB At¬ 
tacks, EWT-3c, OSRD No. 5176c, Effects of Weapons 
on Targets, Yol. 3, NDRC, June 1945. 

115 6B2 The Probability of Fire-Starting by In¬ 
cendiary Bombs, I: General Principles and Methods, 
EWT-5b, OSRD No. 5405b, Effects of Weapons on 
Targets, Yol. 5, NDRC, August 1945. 

116. 6B2 The Probability of Fire-Starting by In¬ 
cendiary Bombs, II: Estimates for the Mlffl Incendiary 
Bomb, EWT-5c, OSRD No. 5405c, Effects of Weapons 
on Targets, Yol. 5, NDRC, August 1945. 

117. 6B2 The Probability of Fire-Starting by In¬ 
cendiary Bombs, III: Estimates for the M50 Incen¬ 
diary Bomb, EWT-5d, OSRD No. 5405d, Effects of 
Weapons on Targets, A 7 ol. 5, NDRC, August 1945. 

118. 6C1 Air Attack on Steel Mills, EAVT-6d, 
OSRD No. 5657d, Effects of Weapons on Targets, 
Yol. 6, NDRC, September 1945. 

119. 6C2a Attack on Dams, EWT-5f, OSRD No. 
5405f, Effects of Weapons on Targets, Yol. 5, NDRC, 
August 1945. 

120. 6C2b Attack on Penstocks, EWT-2b, OSRD 
No. 5045b, Effects of Weapons on Targets, Yol. 2, 
NDRC, May 1945. 

121. 6D1 Attack on Open Gun Einplacements, 
EWT-6a, OSRD No. 5657a, Effects of Weapons on 
Targets, Yol. 6, NDRC, September 1945. 

6D2 References are listed on the Data Sheet. 

122. 6D3 MAE’s Calculated from Ashley Walk 
Trials, EWT-6b, OSRD No. 5657b, Effects of Weap¬ 
ons on Targets, Yol. 6, NDRC, September 1945. 

123. 6E1 The Padius of Damage for Underground 


Services. RC 290, Ministry of Home Security (Brit¬ 
ish), November 1941. 

124. 6E1 Final Report 6f Bombing Tests on Un¬ 
derground Piping, Corps of Engineers, IT. S. Army, 
May 1942. 

125. 6E1 Aerial Bombing Attacks Against Aero¬ 
dromes—Runways and Landing Grounds, EWT-lc, 
OSRD No. 4918c, Effects of Weapons on Targets, 
Ami. 1, NDRC, April 1945. 

126. 6F2 Attack of Railroads, EWT-2d, OSRD 
No. 5045d, Effects of AYeapons on Targets, A 7 ol. 2, 
NDRC, May 1945. 

127. 6F3 Air A ttack on Bridges, EWT-3j, OSRD 
No. 5176j, Effects of Weapons on Targets, A 7 ol. 3, 
NDRC, June 1945. 

128. 6E4 Attack of Tunnels, EWT-2e, OSRD No. 
5045c, Effects of AYeapons on Targets, Yol. 2, NDRC, 
May 1945. 

Tentative Data—Performance of Large Bombs 

Sheet 7A1 gives tentative data for performance of 
the 12,000-lb GP bomb T10 and the 22,000-lb GP 
bomb T14. These bombs are essentially the same as the 
British bombs Tallboy-M and Grandslam except that 
the IT. S. bombs are filled with Tritonal instead of 
Torpex D-l. Performance predictions are estimated by 
extrapolation of the data given in the sheets in Sec¬ 
tions 2, 3, and 6 of this book, with use being made of 
the observed performance of the British bombs where 
possible. The estimated performance in perforation of 
concrete, perforation of armor, and cratering in soil 
agrees very well with the observed performance of the 
British bombs. No observations of performance for 
other effects have been reported. Copies of principal 
papers describing the characteristics and performance 
of the British Tallboy-M and Grandslam and a critical 
discussion of these bombs may be found in refer¬ 
ence 129. 

129. Study of the Requirements, Employment, 
and Effectiveness of Large Bombs, AAF Project No. 
4614A471.6, the Army Air Forces Board, Orlando, 
Fla., April 1945. 

Miscellaneous Information 

Sheet 0M1 gives a graphical method for solving the 
spherical triangle by which the altitude of the sun is 
determined at any point on the earth’s surface and at 
any date. From the graphs, the ratio of object height 
to length of shadow on level ground can be determined 
to a good approximation. The only information that 
is needed is the latitude and longitude of the place in 
question, and the date and Greenwich Civil Time 


* 









354 


WEAPON DATA SHEETS 


when the shadow was measured. This sheet is useful 
in determining heights of buildings from aerial photo¬ 
graphs. Data on solar declination and Greenwich 
Hour Angle are from reference 130. 

130. Marine and Air Navigation, J. Q. Stewart 
and M. Pierce, Ginn & Co., New York, 1944. 

The detailed calculations for sheet 0M2 are given 
in reference 131. 

131. Bombing Densitg Calculations for Sloping 
Targets, EWT-3g, OSRD No. 5176g, Effects of Weap¬ 
ons on Targets, Yol. 3, NDRC, June 1945. 

Incident Summaries 

The Incident Summaries are based on the refer¬ 
ences listed below, the number of the Incident Sum¬ 
mary being listed with the reference number. 

132. A550 Air Baid Damage Beport, Serial No. 
A.2, Ministry of Home Security, February 1943. 

133. A1100 Air Baid Damage Beport, Serial No. 
A.3, Ministry of Home Security, February 1943. 

134. A3100 Air Baid Damage Beport, Serial No. 
A.5, Ministry of Home Security, February 1943. 

135. A-pm Air Baid Damage Beport, Serial No. 

A. 7, Ministry of Home Security, February 1943. 

136. B110 Air Baid Damage Beport, Serial No.B.l, 
Ministry of Home Security, February 1943. 

137. B550 Air Baid Damage Beport, Serial No. B.2, 
Ministry of Home Security, February 1943. 

138. B2200 Air Baid Damage Beport, Serial No. 
BA, Ministry of Home Security, February 1943. 

139. B-pm Air Baid Damage Beport, Serial No. 

B. 7, Ministry of Home Security, February 1943. 

C110 See reference 101 
C550 See reference 102 
Cl000 See reference 106 
Cl 100 See reference 96 
C2200 See reference 97 

140. DUO Air Baid Damage Beport, Serial No. 
D.l, Ministry of Home Security, February 1943. 

141. D1100 Air Baid Damage Beport, Serial No. 
D.3, Ministry of Home Security, February 1943. 
D2200 See reference 103. 

142. D-pm Air Baid Damage Beport, Serial No. 
D.7, Ministry of Home Security, February 1943. 

General References 

The following publications contain much general 
material similar to that in Weapon Data—Fire, Im¬ 
pact, Explosion or contain information of general in¬ 
terest on the effectiveness of weapons. Much of the 
material in these works and in the present report is 


based on the same sources, and in many instances the 
interpretation used in one of the reports is taken 
directly from one of the others. Such repetition of in¬ 
formation and interpretation should by no means be 
interpreted as lending authenticity to the material. 

143. Selection of Bombs and Fuzes for Bombard¬ 
ment Targets, the Army Air Forces Board, Project 
No. 3554A471.6, the Army Air Forces Board, Or¬ 
lando, Fla., October 1944. 

144. The Belative Effectiveness of V arious Type 
Bombs and Fuzes Against Strategic and Tactical Ob¬ 
jectives, Army Air Forces Evaluation Board, Mediter¬ 
ranean Theater of Operations, October 1944. 

145. Selection of Bombs and Fuzes to be Used 
Against Various Targets, OPNAY-16-Y JA6, Air 
Intelligence Group, Division of Naval Intelligence, 
Office of the Chief of Naval Operations, Navy Depart¬ 
ment, Washington, March 1944. 

146. Selection of Bombs and Fuzes for Destruction 
of Various Targets, FM 1-110; FTP 224, War and 
Navy Departments, Washington, April 1945. 

147. Ballistic Data, Performance of Ammunition, 
TM 9-1907, War Department, Washington, Septem¬ 
ber 1944. 

148. Selection of Weapons for Fighter Bombers 
Against Tactical Targets, Operations Research Sec¬ 
tion, Ninth Air Force, Memorandum No. 70, Feb¬ 
ruary 1945. 

149. Effects of Explosion of HE Bombs: I. Gen¬ 
eral and Air Blast, BRL Report No. 554, Ballistic 
Research Laboratory, Aberdeen Proving Ground, Md., 
June 1945. 

150. Performance of Bombs and Projectiles Against 
Shore Installations, Ordnance Pamphlet 1172, Bureau 
of Ordnance, Navy Department, Washington, May 

1944. 

151. Air Attach of Japanese Coast Defense Batter¬ 
ies, Target Analysis, CINCPAC-CINCPOA Bulletin 
No. 17-45, February 1945. 

152. Effects of Weapons on Targets, Volumes 1-6, 
Divisions 2 and 11 and the Applied Mathematics 
Panel, NDRC, monthly publication, April-September 

1945. 

153. Study of the Physical Vulnerability of Mil¬ 
itary Targets to Various Types of Aerial Bombard¬ 
ment, NDRC Report No. A-385, OSRD Report No. 
6444, Division 2, NDRC. 

154. Effectiveness of U. S. Incendiary and High 
Explosive Bombs, NDRC Report No. A-386, OSRD 
Report No. 6445, Divisions 2 and 11 and the Applied 
Mathematics Panel, NDRC. 










/ 


WEAPON DATA 
FIRE, IMPACT, EXPLOSION 




355 








Foreword 


WEAPON DATA 


I: Attacking Weapons 

Physical Characteristics: 

Explosive Fillings - Properties & Uses.I Al 

U.S. Bombs & Fuzes - Fuze Characteristics.I A3 

American - HE Bombs.. I A3a* 

American - Incendiary Bombs.| A3b 

American - Incendiary Bomb Clusters.I A3c 

American - Depth Bombs, A/C Mines, Torpedoes... I A3d 

British - HE Bombs.I A4a 

German - HE Bombs.I A5a 

German - Incendiary Bombs, Mines.I A5b 

Japanese - HE and Incendiary Bombs.I A 6 * 

American - Land Mines and Firing Devices.I A7a 

American - Demolition, Shaped, Line Charges....! A7b 

Striking Velocity and Angle of Impact: 

Low Level Bombing. .I B4 

100 - I b GP, AN-M30; 250- I b GP, AN-M57.I B5* 

500-lb GP, AN-M64; 500-1 b SAP, AN-M58.I B 6 * 

1 000 -lb GP, AN-M65; 1000 -lb SAP; AN-M59.I 87* 

1000-lb AP, AN-Mk33; 1000- I b AP, M52AI.I B 8 * 

I 600-lb AP, AN-Mkl; 2000-1 b GP, AN-M 66 .I B9* 

2000-lb SAP, Ml 03; 4000-lb LC AN-M56.I BIO* 

12 , 000 -lb GP, TIO; 22 , 000 -lb GP, TI4.I BI2 

90-lb Frag. AN-M82; 260-lb Frag. M81.I BI5 

Flight Characteristics of IB's, l 8 Clusters....i B 20 

100 -lb IB, AN-M47; 500-1 b IB, AN-M76.I B21 

Aircraft Loading: 

Incendiary Bombs and Clusters.I Cl 


2: Impact 


Penetration 

Reinforced Concrete by Bombs & Projectiles. 2 AI 

Bombs into Soil. 2 A2* 

Bombs and Small Caliber Bullets into Soil. 2 A2a 

Projectile Ballistic Limits and Craters. 2 A3 

Ricochet from Water, Soil & Concrete. 2 A5 

Scabbing: 


Reinforced Concrete by Bombs and Projectiles... 2 Bl 

Perforation: 

Reinforced Concrete by Bombs and Projectiles...2 Cl 
Reinforced Concrete by Specific Bombs &Rockets.2 CI a 


Plastic Protection. 2 C2 

Homogeneous Armor by Projectiles. 2 C3 

Homogeneous Armor by American Projectiles. 2 C3a 

Homogeneous Hard Armorby Ca .30 & .50 Bui lets.. 2 C4 

Homogeneous Armor by Bombs (General). 2 C5* 

Homogeneous Armor by Specific Bombs. 2 C5a 

Homogeneous Armor by TC Cored Projectiles. 2 C6 

Homogeneous Armor by German Projectiles. 2 C7 

Mild Steel by Uncapped AP Projectiles. 2 C8 


3: Explosion 

Air Blast: 


Maximum Peak Pressure. 3 A I 

Positive Impulse. 3 A2* 

Impulse due to Det. of Bombs, Ground Level. 3 A2a 

Side-on vs Face-on Measurement. 3 A3 

Impulse - Contact Explosions. 3 A4 

Cone-end Charges against Concrete. 3 A5 

Cone-end Charges against Homogeneous Armor. 3 A6 

Mach Reflection. 3 A7 

Optimum Height for Maximum Impulse. 3 A8 

Pressure i Impulse on Ground due to Air Burst.. 3 A9 

Earth Shock 

Craters in Soil - Diameter and Depth. 3 Bla* 

Cratering by Line Charges. 3 Bib 

Earth Displacement. 3 B2 

Underground Pressure and Impulse. 3 B3* 

Underwater: 

Pressure and Impulse. 3 Cl 

Maximum Radius of Bubble. 3 C2 


* revised data sheets replacing former equivalent sheets 


Table of Contents 

Final Edition 


6: Target Vulnerability 


Impulse Criterion: Damaqe Levels. 6 AO 

Components of Structures: 

Steel Columns - Blast Damage. 6 Ala* 

Concrete Columns - Blast Damage. .6 Alb* 

Concrete Floor Slabs - Blast Damage. 6 A2 

Sheet Roofing - Removal by Blast. 6 A3* 


Underground R/C Walls - Damage by Earth Shock_ 6 A5* 

Reinforced Concrete Walls - Damage by Air Blast. .6 A6* 


Industrial Buildings: 

Damage by HE Bombs. 6 Bl 

Damage by Incendiary Bombs. 6 82 

Special Industrial Targets: 

Bombing of Steel Mi Its. 6 Cl 

Bombing of Dams.6 C2a 

Bombing of Penstocks. 6 C2b 

Mi 1itary Targets: 

Bombing of Gun Positions. 6 Dl 

Passage of Wire and Obstacles. 6 D2 

Frag. Damage - Aircraft, Vehicles, Personnel. 6 D3 

Util itiee: 

Underground Piping. 6 El 

Transportation: 

Bombing of Airfield Runways. 6 FI 

Ai r Attack on Rail roads. 6 F2 

Bombing of Bridges. 5 F3 

Bombina of Tunnels .6 F4 

7: Bomb Performance: 

12,000-lb GP, TIO; and 22.000-lb GP, T 14. 7 Al 


APPENDIX 

Mi seel Ianeous: 


Solar Shadow Ratio Chart. 0 Ml 

Equivalent Horizontal Area for Sloping Target. 0 M2 


Incident Summaries: 


A*. (MS-SF) Multi-story, Steel Frame Construction 

550-lb GP Bomb - Office Building.A 550 

1100-lb GP Bomb - Apartment Building.A MOO 

3 I 00-I b AP Bomb - Railway Station.A 3100 

Parachute Mine - Office Building.A Para- 

mine 

B: (SS-SF) Single-story, Steel Frame Construction 

110-lb GP Bombs - Shed Buildings.B NO 

550-lb GP Bombs - Factory Building.B 550 

2200-lb GP Bomb - Factory Building. 8 2200 

Parachute Mine - Office Building.B para- 

mi ne 

C: (MS-RCF) Multi-story, R/C Frame Construction 

I 10— lb GP Bomb - School Building.C NO 

550-lb GP Bomb - Warehouse.C 550 

1000-lb GP Bomb - American Test Bui lding..C 1000 

I I 00-I b GP Bomb - Apartment Building.C MOO 

2200-I b GP Bomb - Warehouse.....C 2200 


D: (MS-WB) Multi-story, Wall Bearing Construction 


I 10-1b GP Bomb - School Building. 
I 100-Ib GP Bomb - Office Building 

2200-lb AP Bomb - Warehouse. 

Parachute Mine - Factory Building 

Sources of Information 


D NO 
D I 100 
D 2200 
D para- 
mi ne 


M 


V7\7 


TyTj 


357 





























































































































































































































































































































































* i 




























* 

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WEAPON DATA 

EXPLOSIVE FILLINGS FOR WEAPONS: 
PROPERTIES AND USES 


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rt W B 


SEPTEMBER 1945 


359 


and pressure of the detonation. 
















































WEAPON DATA 


UNITED STATES BOMBS AND FUZES 


r 


J 

A 

„ page one 

k u.s. 

BOMBS & FUZES , 


ABBREVIATIONS: 

primer-det 

- primer-detonator 

Inst - instantaneous 

adap. bstr 

- adapter booster 

mech - mechanical 

aux. bstr 

- auxi1iary booster 

mod(s) - modif ication(s) 

CV 

- aircraft carrier 

v. rev - vane revolutions 

arm. 

- arming 

air tr - air travel 

imp. 

- impact 

pyro - pyrotechnic 

A/C 

- aircraft 

* Time is given in seconds unless noted otherwise. 

ie: feet of water, hours or minutes. 

** if air burst setting fails to function, these fuzes will function instantaneously up- 

on impact, providing fuze is armed. 




NOTE: The nominal functioning time and 

the actual 

range of functioning 

t ime 

of some of the important fuze settings. 

determined 

from static 

firing 

test 

data, are given below: 






NOMINAL FUNCTIONING TIME, seconds ACTUAL RANGE 

OF 

FUNCTIONING 

TIME, seconds 

Inst. (av. 0.001). 

0.000 

to 

0.003 



Non-delay (av. 0.003). 

0.0025 

to 

0.006 



0.01 . 

0.008 

to 

0.013 



0.025 . 

0.018 

to 

0.032 



0.1 . 

0.100 

to 

0.150 



0.24 . 

- 


- 




A- BOMB-FUZE COMBINATIONS for High Explosive Bombs 


ARMY "M" and ARMY-NAVY "AN-M" BO€S 


BOMB 

NOSE FUZE 

TAIL FUZE 

model 

model 

functioning 

model 

functioning 

number 

number 

time, seconds* 

number 

time, seconds’ 


FRAGMENTATION BOMBS - F 


4-lb, F 

M83 

"Butte rf1y" 



Ml 29 

T48 El 
(MOO) 

T49 
(MI3I ) 

impact or 

air burst** 

10; 20; 30; 
m mute s 

ant i- 
d isturb. 

20-lb, F 

AN-M41 AI 

Ml 10 

AN-MI10 AI 

i nst. 

- 

- 

23—lb, F 

AN—M40 AI 
M72 AI 

AN-MI 04 
AN-MI20.AI 

1 nst ► 

“ 

- 

90-lb, F 

M82 

AN-M103,A 1 

Ml 63 

MI35 

1nst., (0. 1) 

5-92 air burst 

** 

10-92 air burst 

5-30.6 
air burst** 
10-30.6 
ai r burst** 

Inst.;(O.Ol) 
Inst.; (0.025) 

; 

- 

220-lb, F 

M88 

260-lb, F 

AN-M61 

Ml35 AI 

MI36 

MI36 AI 

H139,A1 ; Ml 64 

M140,A1 ; M165 

AN-MI00 AI 
AN-M100 A2 
MI60 

non-de1 ay; 

(0.01; 0.025; 

0. I;0.24) 

120-lb, F 

M86 

AN-MI04 

AN-M120,A 1 

1 nst. 

Inst. 


- 

FRAGMENTAJ1 ON CLUSTERS - FC 

100-lb, FC 

M28 

500-lb, FC 

M29 

500-lb, FC 

M26 

500-lb, FC 

M27 

Ml 1 1 

Mill AI 

Mill A2 

15-93 

air burst** 

5-92 

air burst*’ 


- 

MI46- 5.92 air burst** used 
in M28 A M29 only. 


Ml 65 - 5.92 air burst** used 
i n M26 & M27 only. 


GENERAL PURPOSE BOMBS - GP 


100-lb, GP 

AN-MI03.AI 
Ml 63 

Ml 35 

Ml 35 AI 

AN-M30, A 1 


250-lb, GP 

Ml 36 

AN-M57,AI 


500-1b, GP 

MI36 AI 


AN-M43 
AN-M64,A I 

1000-1b, GP 
AN-M44 
AN-ti65,A I 

2000-lb, GP 

AN-M66,A I 


MI39,AI;MI64 
Ml 40,A f;M165 

MI49 


AN-Mk219 

Mk232 -I 

(special) 

Mk239-0 
Mk243.0 


Inst.; 0.1 
5-92 

ai r burst” 
10-92 

air burst** 

5-30.6 

ai r burst** 

10-30.6 
air burst** 

Inst.; 0.01 
Inst; 0.025 

Blast Pres¬ 
sure. .. see 
fuse table 

I nst 

Inst or 
elec.impuIse 

0.01 

0.025 


AN-MI00,AI,A2 
A MI60 series 

Ml 12 series 
Ml 12A I series 
Ml 15 serIes 
HI 23, AI series 
MI32 series 

AN-Mk230 

I AN-M64.65.66 
A AI series) 

Mk23l-0 

(A»-M64,AI ) 

Mk237-0 

(AN-M64,A I ) 

Mk238-0 

IAN-M65,AI; 
AN-M66,A I ) 
4k240 
AN-M65, AI; 
AN-M66, A I 1 


non-deI ay; 
0.01;0.025; 

0.I; 0.24 
4-5; 8-11 
4-5; 8-1 I; 8-15 
4-5;8-1 I;8-1 5 
1-144 hrs 
10 minutes 

25-125 ft 
of water 

25 ft of 
water 

2; I0;30 firs 


2;10;30 hrs 


25 ft of 
water 


100-lb, GP 
250-lb, GP 
500-lb, GP 


Anti-ricochet Bombs 


MI5I 


8-15 


LIGHT CASE BOMBS - LC 


*000-1b, LC 

AN-M56 

AN-MI03,A1 

MI35 

Ml35 AI 

Ml 36 

Ml36 AI 

MI39.AI 

MI40.AI 

MI49 

AN-Mk219 

Inst, only 

5-92 air b'st Jf 
10-92 air b'st^ 
5-30.6 air b'st 
10-30.6 air b'st 
Inst, only 

Inst, only 

Blast Pressure 

1 nst. 

AN-MI02 AI 
AN-M102 A2 
Ml 62 

non-de1 ay 
.{to avoid 
b reak-up 
of bomb 
case ) 


SOURCE: 

Publications of the U.S.Navy and U.S.Army Bomb Disposal Schools and the 
Ballistic Research Laboratory, U.S.A., Aberdeen Proving Ground, Md. 


ARMY "M" and ARMY-NAVY "AN-M" BOMBS (continued) 


BOMB 

NOSE 

FUZE 

TAIL 

FUZE 

model 

model 

functioning 

model 

functioning 

number 

number 

time, seconds* 

number 

time, seconds * 


SEMI-ARMOR-PIERCING BOMBS - SAP 


500-lb, SAP 

AN-M58 

AN-M58 AI 
AN-M58 A2 

AN-MI03,A1 
MI63 

(M135) 

(MI35 AI) 
(Ml36) 

(Ml36 AI) 

Ml 39,A 1 
MI64 

Ml 40,A 1 
MI65 

(MI49) 

AN-Mk 219 

(Mk 232-1 

special ) 

Mk239-0 

Mk243-0 

1 Inst I; 0. 1 

(5-92 air b'st) 

1 10-02 ai rb'st) 

15-30.6 a i r b 'st I 

I 10-30.6 ai r b'st 

1 Inst ); 0.01 

AN-MI01 AI.A2 
MI6I 

Ml 13 

Ml 13 AI 

Ml 16 

Ml 24,A1 

Ml 33 

non-de1 ay; 

0.01; 0.025; 

0.1; 0.24 

4-5; 8-1 1 

4-5; 8-1 1; 8-15 

4-5;8-1If 8-15 

1-144 hrs 

10 minutes 

1000-lb, SAP 

AN-M59 

AN-M59 AI 

2000-1b, SAP 

MI03 

1 no nose 

fuzes) 

I Inst ); 0.025 

I8last Pressure! 

(Inst. I 

(1nst or 
elec, impulse) 

O.Ol 

0.025 

AN-MI02 AI,A2 
MI62 

Ml 14 

Ml 14 Al 

Ml 17 

M125, A1 

Ml 34 

non-de1 ay 

0.01;0.025; 

0.1; 0.24 

4-5; 8- 1 1 

4-5; 8-1 1; 8- 15 

4-5; 8-1 1; 8- 15 

1-144 hrs 

10 minutes 

NAVY "Mk" and 

ARMY-NAVY " 

AN-Mk" BOMBS 




GENERAL PURPOSE BOMBS - GP 


100-lb, GP 

Mk 4 A mods 

(obsolescent ) 

AN-Mk219 

Mk233 

(special) 

1 nst 

elec, impulse 

- 

- 

• 

AN-Mk219 

Mk221 

Mk232 -1 

(special) 

1 nst 

0.01 

Inst or 
elec, impulse 

Mk223 

0.01 

500-lb, GP 

Mk239-0 

0.01 

Mk229 

25-125 ft 

Mk 12 & mods 

Mk243 

0.025 

of water 

( obsolescent) 

AN-MI03,A1 

1 nst; 0.1 

AN-MI02 A1.A2 

non-de1 ay; 

0.01;0.025; 

1000-lb, GP 

MI63 

Ml 35 

5-92 air b'st 

Ml 62 

0. 1; 0.24 

Mk 13 & mods 

• B 

Ml 14 

4-5; 8- 1 1 

( obsolescent 1 

Ml35 AI 

10-92 air b'st 


Ml 36 

5-30.6 air b'st 

Ml 14 AI 

4-5; 8-1 1; 8- 15 


Ml36 AI 

10-30.6 air b'st 

Ml 17 

4-5; 8-1 1; 8- 15 


AN-MI39.AI 

MI64 

AN-MI40,A 1 
MI65 

M149 

Inst; 0.01 

Inst; 0.025 

Blast Pressure 




ARMOR-PIERCING BOMBS - AP 


1000-lb, AP 

AN-Mk33 

1600-lb, AP 

AN-Mk1 

- 

- 

AN-Mk228 

AN-MI02 AI.A2 
MI62 

0.08 

non-de1 ay; 

0.01;0.025; 

0. 1; 0.24 

DEPTH BOMBS - DB 

325-lb, OB 

AN-Mk17' 

AN-Mk41 

AN-Mk44 

AN-Mk47 

(obso1escent) 

AN-Mk219 

Mk232 -1 

(special) 

AN-MI03,A1 
MI39.AI 
AN-MI40.AI 

Ml 49 

MI63 

Ml 64 

1 nst 

Inst or 
elec, impulse 

Inst; (0. 1 ) 

Inst; (0.01) 

Inst; (0.025) 

Blast Pressure 

Inst; (0.1) 

Inst; (0.01) 

AN-Mk224 
AN-Mk234 
(Athwartship 
fuzes) 

25-125 ft 
of water 

325-lb, DB 

Mk53 

350-lb, DB 

Mk54 

AN-Mk230 

Mk 231—0 

25-125 ft 
of water 

25 ft of 
water 

650-lb, DB 

Mk37 

Mk38* 

700-lb, DB 

Mk49 

(obsolescent) 

AN-Mk224 

AN-Mk234 

(Mk38, 49 only) 
(At hwa rtship) 

Mk229 

AN-Mk230 

25-125 ft 
of water 


ANTI-AIRCRAFT BO 

MBS - AA 



5-lb, AA 

Mk34 

Mk227 

1 nst 

- 

- 


NOTE: 

Parentheses ( ) enclosing functioning time or fuze number indicate that use is 
possible but unlikely or not recommended. 


360 


j 


PTM No. 109 
April 1945 


































































































S M Ml US A - f* r > 



B'FUZE CHARACTERISTICS fror High Explosive Bomb Fuzes) 


ARMY "M" and ARMY-NAVY "AN-M" FUZES 


MODEL 

NUMBER 


TYPE 


NOMINAL 
FUNCTIONING 
TIME ,seconds 


ARMING TIME 
OR D ISTANCE./i 


MIN.ALT. 
TO ARM AT 
200 mphUt 


BOMBS USED IN: 


COMPANION 

FUZE 


ADDITIONAL 

COMPONENT 

PARTS 


REMARKS 


AH-MIOO A I 


AN-MIOO A2 


AN-MIOI A I 


AN-MIOI A2 


AN-MI02 A I 


AN-MI02 A2 


Tail: 

mech. impact 


non-de1 ay 

0.01 

0.025 

0.1 

0.24 


720 v .rev 


150- 170 v. rev 
445-485 air tr 


720 v.rev 


150-170 v.rev 
555 air tr 


720 v.rev 


150-170 v.rev 
465-665 air t r 


40-50 


60-70 


85 


100 GP, AN-M30,AI; 
250 GP; 220 F; 260 F 


500 GP, AN-M43(64AI); 
500 SAP 


AN-MI 03 
Mk243 


1000 GP; 500 GP,Mk12; 
2000 GP; 1000 SAP; 
4000 LC 


M I 4 

p r i me r-det 
Ml 02 adap 
bstr with 
Navy GP's 


non-delay only for 260 F, 

4000 LC.for GP's and 

SAP's delays are governed 

by tact ical use.the 

AN-MIOO AI series can be 
prearmed 350 v. rev; this 
series is obsolescent 


AN-M103 


Nose: 

mech. impact 


AN-MI03 A I 


Inst. 

0.1 


inst: 330 v„rev 
760-1600 air tr 

0.1: 220 v.rev 

510-1080 air tr 


I nst: 
450 

0. I: 
210 


All depth bombs, GP's 
(except 100 GP, Mk4) 
and 90F(except MI03) 
220 F, 260 F...may be 
used in SAP's for 
frag effects; results 

are inconsistent. 

4000 LC 


AN-MIOO AI, 
A2 series 


usable for dive bombing, 
not recommended for mast¬ 
head attack..AN-M103: not 
crash-proof,unsafe for CV 
use..AN-MI03 Al:is crash¬ 
proof, safe for CV use... 
modified arming vanes re¬ 
quired for use with flat 
nose bomb 


AN-MI04 


Nose: 

mech. impact 


Inst. 


2.5 seconds 
py rotechn i c 


80 


23 F, AN-M40; 
120 F, M86 


M72 


sensit ive mushroom striker 
head. .. .being replaced by 
AN-M I 20, AI ..unsafe for CV 
use 


Ml 10 


AN-MI10 AI 


Nose: 

mech. impact 


570 v.rev 


Inst. 


260 v.rev 


60 


20 F, AN-M4I 


unsafe for CV use...alter¬ 
nate for AN-MI03 using 
Ml 17 adapter booster 


Ml I I 


Mill AI 


Mill Ai 


Nose: 

mech. time 
aerial burst 


15-93 
imp. inst 


5-92 

imp. inst 


5-92 

imp. inst 


570 v.rev 


450 


570 v.rev 


450 


260 v.rev 


185 


500 F Clusters: 

M26 (20 - 20 F's) 

M27 ( 6 - 90 F's) 

M29 (90 - 4 F's) 

100 F Cluster: 

M28 (24 - 4 F's) 


not detonator safe...obso¬ 
lescent; being replaced by 
T55 E2 (MI 46)4 T7 I (MI55) 


Ml 12 


4-5 

8-11 


MI6 

p rime r-det 


Ml 12 AI 


4-5 

8-11 

8-15 


100 GP, AN-M30, AI; 
250 GP 


MI6;MI6 A I 
p rime r-det 


Ml 13 


MM3 AI 


Tail: 

mech. impact 
pyro. delay 


4-5 

8-11 


MI6 

prime r-det 


4-5 

8-11 

8-15 


15-20 v.rev 
100 air t c 


500 GP; 500 SAP 


MI6;MI6 AI 
p rime r-det 


Ml 14 


4-5 

8-11 


Ml 14 AI 


4-5 

8-11 

8-15 


1000 GP; 1000 SAP; 
2000 GP; 500 GP, Mk12 
1000 GP, Mk 13 4 mods 
using MI02 adapter 
bstr 4 spacer ring 


these fuses (Ml 12-MI 14,4 
mods) are supersensitive 
min.altitude bombing fus¬ 
es and wiI I function at 
impact angle of 3*-unsafe 
for CV use...MI02 adapter 
booster used with Navy 
GP's 


MI6 

p rime r-det 


Ml 6; Ml6 A I 
p rimer-det 


Ml 15 


150-170 v.rev 
485 air t r 


Ml 16 


Tail: 

mech. impact 
py ro . del ay 


4-5 

8-11 

8-15 


150-170 v.rev 
555 air t r 


Ml 17 


I 50-170 v.rev 
665 air t r 


40-50 


60-70 


85 


100 GP; 250 GP 


500 GP; 500 SAP 


1000 GP; 2000 GP; 
1000 SAP; 500 GP, 
Mk 12; I000GP, Mk 13 


MI6;MI6 A I 
prime r-det 
Ml 02 adap . 
bstr. with 
Navy GP's.. 


minimum altitude bombing 
fuses.safe for CV use 


AN-MI20 


AN-M 120 AI 


Nose: 

mech. impact 


Inst. 


2.5 sec(±0.25) 
mech. delay 


1.9 sec(±0.15) 
mech. delay 


23 F, AN-M40 AI, 
M72 AI; 120 F, M86 
using Ml 17 adapter 
booster 


none 


unsafe for CV use.not 

available in Navy clusters 
..for lower level attack, 
the AN-M 120 AI is preferred 


Ml 23 


75.6- 190 v. rev 
370 air t r 


180 


MI23 AI 


Ml 24 


Ml24 AI 


MI25 


Tail: 

chem. time 
anti-removaI 
(Ai series: 
direct drive; 
earl ter mods: 
year reduct) 


4-6 v. rev 


I00GP,AN-M30.AI;250 GP 
220 F; 260 F 
(A I mods preferred) 


MI9 

p rime r-det 


I. 2, 6, 
12,24,36, 
72,144 
hours 


75.6-190 v.rev 
370 air tr 


215 


4-6 v.rev 


500 GP; 500 SAP (A I 4 
A2 mods preferred) 


anti—dis— 
tu rbance 
nose fuse 
is being 
deveI oped 


Mi9 A2 
p r i mer-det 


MI9 

prime r-det 


Ml9 A2 
p ri mer-det 


75.6-190 v.rev 
370 air t r 


310 


MI25 AI 


4-6 v.rev 


1000 GP; 1000 SAP; 
2000 GP (A I and A2 
mods preferred) 


MI9 

p rime r-det 


chemicals in glass ampoule 
considered armed if dropped. 
..sensitive to temperature 
changes..not to be used in 
temp, over I20°F...deI ays 
vary with concent rat i on of 
a I coho I-acetone solution 4 
thickness of ceI I uI oid d isc 
.equipped with ball-lock¬ 
ing anti-removal device... 
cannot be fyrearmed 


Ml9 A2 
prime r-det 


MI29 


ground or 
air burst 


Impact or 
air burst 


2.5 seconds 


4 F,M83 "Butterfly’ 


impact has slight inherent 
deI ay....fuse is shipped 
i nstalied' in bomb 


EBmS 




361 




















































































































































B-FUZE CHARACTERISTICS (continued) 


ARMY "M" and ARMY-NAVY "AN-M" FUZES (continued/ 


MODEL 

NUMBER 

TYPE 

NOMINAL 

FUNCTIONING 

TIME ,seconds 

ARMING TIME 

OR DISTANCE ,ft 

MIN.ALT. 
TO ARM AT 
200 mph Jt 

BOMBS USED LN: 

COMPANION 

FUZE 

ADDITIONAL 

COMPONENT 

PARTS 

REMARKS 


T48 tl 
(MI30) 

mech. time 

10,20,30 

minutes 

3i rotations of 
arming spindle 


4 F,M83 "Butterfly" 

none 

none 

setting pre-set at factory 
..fuse is shipped installed 
in bomb 

T49 
(M1 3 1 ) 

ant i - 

d i sturbance 

- 

about 5 secs, 
after impact 


4 F.M83 "Butterfly" 

none 

none 

supersensitive; vibrations 
from nearby A/C propeller 
sufficient to fire fuse... 
fuse is shipped installed 
in bomb 

Ml 32 

Tail: 

chem. time 
ant i - removal 

10 minute 
nominal 
delay.... 
range of 

6-80 min. 
delay due 
to temp, 
var iation 

63-84 v.rev 

300 air t r 


100 GP, AN-M30 ,AI; 250GP 

none 

MI9 

prime r-det 

similar to MI23 series,but 
safer in that solvent is in 
copper bellows instead of 
glass ampou1e..de1 ays vary 
with change of temperature 
but always sufficient to 
allow forward planes of 
large formations to drop 
bombs from low altitude 
without endangering rear 
p1anes .... has ball-locking 
anti-removal device 

Ml 33 

63-84 v.rev 

370 air tr 

500 GP,AN-M64,A1; 

500 SAP 

M19 

prime r-det 

Ml 34 

63-84 v.rev 
300-450 air tr 

1000 GP,AN-M65,AI; 

1000 SAP; 2000 GP 

Ml 35 

Nose: 

mech. time 
ai r burst 

5-92 or 
imp.inst. 

app roximate 1y 

260 v. rev 

750 air t r 


All GP's (except 

100 GP Mk4) 4000LC, 
may be used in 90 F, 
220 F and 260 F 
(and SAP's) 

no rma11y 
none,un less 
AN-M100 A2 
series is 

used as an 

i nsurance 
fuse 

none 

Setting can be adjusted to 

0. 1 second.will f i re 

accurately to + one sec... 
detonator safe; not suit¬ 
able for naval use....min. 
setting of 10 sec. recom¬ 
mended 

Ml35 Al 

10-92 or 
imp. inst. 

Ml 36 

Nose: 

mech. time 
air bu rst 

5-30.6 or 
imp.inst. 

app roximate 1y 

260 v.rev 

750 air t r 


All GP's (except 

100 GP Mk4) 4000LC; 
m ay be used in 90 F, 
220 F, and 260 F 
(and SAP's) 

no rma1 1 y 
none,un 1 ess 
AN-MI00 A2 
series is 

used as an 

i nsurance 

fuse 

none 

improved clockwork, more 
accurate than MI35, Al.... 
setting can be adjusted to 

0. 2 second.will f i re 

accurately ±0.3 sec. 

detonator safe; not suit¬ 
able for naval use....min. 
setting of 10 sec recom¬ 
mended 

MI36 Al 

10-30.6 or 
imp. inst. 

Ml 39 

AN-Ml39 Al 

Nose: 

mech. impact 

Inst. 

0.01 

1 nst : 

330 v.rev 
765-1600 air tr 

0.01 A 0.025: 

220 v. rev 

1 nst : 

450; 

0.01 

A 0.025: 
210 

All depth bombs,GP's 
(except 100 GP,Mk4 ) 

A 90 F ,220 F ,260 F .. 
may be used in SAP's 
...4000 LC 

AN-M100 A2 

se ries 

M 1 4 

prime r-det 

companion fuses to AN-MI00 
AZ series with shorter de¬ 
lays than AN-MI03,AI .... 

Ml 39 Al and Ml 40 Al are 
c rash-proof 

Ml 40 

AN-MI40 Al 

Inst. 

0.025 




Ml "6 

Nose: 
c1ockwork 
a i r burst 

5-92 

imp. inst 

approximate 1y 

260 v. rev 


100 F Cluster: 

M28 (24 - 4 F's) 

500 F Cluster: 

M29 (90 - 4 F's) 

none 

none 

detonator safe 

MI48 

Nose: 

mech. impact 

Inst: 

0.1 

same as AN-MI03 

same as 

AN-M103 

Japanese Navy bombs 

none 

modified 
booster cup 

modified AN-M103 

MI49 

Nose: 

blast pres¬ 
sure or 
mech. impact 

see 

remarks 

12 - 13 v. rev 


All GP's (except 

100 GP, Mk4); 4000 LC 
(and SAP's) 

none 

none 

•first bomb of stick deton¬ 
ates on impact; remainder 
by blast pressure of pre¬ 
ceding bomb - about 25 -ft 
apart for 500 GP dropped 

in train of 0.05 sec. inter¬ 
vals, air speed 200 mph, 

altitude 10,000 feet . 

detonator safe 

MI5I 

Tail: 

mech. impact 
pyro. delay 

8-15 

approximately 

12 v.rev 


100, 250 GP (ant i- 
r icochet) using M7 
parachute and M202 
fuse adapter; 500 

GP (anti-ricochet) 
using M6 parachute 

A M200 fuse adapter 

..... 

none 

MI6 Al 
primer-det 

similar to MII2 Al series 
with transverse arming stem 
and anemometer vane 

Ml 55 

Hose: 

mech. time 

air burst 

5-92 
imp. inst 

6-9 v.rev 


500 F Clusters: 

M26 (20 - 20 F's) 

M27 ( 6 - 90 F'S) 

none 

none 

supercedes Mill A2 with 
omission of gear reduction 
system resulting in quick¬ 
er arming 

Ml 60 

Tail: 

mech.impact 

non-delay 

0.01 

0.025 

0.1 

0.24 

. 

720 v. rev 

1780-i950 air t r 

650 

100 GP, AN-M30, Al; 

250 GP; 220 F; 260 F 

Ml 63 

Ml 4 

pri me r-det 

Ml 02 

adap.bst r 
with Navy 
GP's 

similar to AN-M 100 series 
except for slower arming 
designed to prevent prema¬ 
ture explosions of bombs 
within range of releasing 
aircraft (especially 629) 
...non-delay only for the 
i 220 F, 260 F and 4000 LC 

Ml 61 

720 v.rev 
1910-2230 ai r tr 

805 

500 GP, AN-M43 (64 Al ) 
500 SAP 

Ml 62 

720 v.rev 

17 10-2600 ai'rtr 

1 130 

1000 GP, AN-M44(65 Al) 
2000 GP; 1000 SAP; 

4000 LC 

Ml 63 

Nose: 

mech.impact 

Inst. 

0.1 

1 nst; 

1710-3625 ai r tr 

0.01 A 0.025: 

1 140-2420 ai r tr 

1775 

915 

All depth bombs,GP's 
(except 100 GP, Mk4) 

A 90 F;220 F; 260 F 
and SAP's 

Ml 60 
series 

none 

similar to AN-MI03, MI39, 

Al, MI40,AI respectively, 
except for slower arming 
des i gned to prevent prema¬ 
ture explosions of bombs 
within range of releasing 
a i rc raft(especia 1 1 y 8295 ) 

M164 

Inst. 

0.01 

MI65 

Inst. 

0.025 






























































































































IV.FUZE CHARACTERISTICS (continued) 



NAVY "Mk" and ARHY-NAVY "AN-Mk 1 FUZES 


MOO EL 
NUMBER 

TYPE 

NOMINAL 
FUNCTIONING 
TIME ,seconds 

ARMING TIME 

OR DISTANCE,/* 

MIN.ALT. 
TO ARM AT 
200 mph Jt 

B0M8S USED IN: 

COMPANION 

FUZE 

ADDITIONAL 

COMPONENT 

PARTS 

REMARKS 

AN-Mk219 
& nods 

Nose: 

mech. impact 
rotor arm. 

Inst. 

170 v.rev 

1100 air tr; 
2000-2500 air 
tr.for flatnose 
depth bombs 


All GP's and DB's 

and SAP's 

GP's 4 SAP's: 
M<223 

(Navy GP's) 
AN-MI00 A2 
and Ml60 
series 

DB's: 

AN-Mk224 

Mk229 

AN-Mk230 

AN-Mk234 

adap.ring 4 
Mk l,aux. bst r 
with all DB's 
and 500 GP, 
Mk 12; 1000 GP 
Mk 13 4 mods 
.. adap. r i ng 
4 Mk4 bstr 
pellet with 
al1 "M" and 
"AN-M" GP'S 

will funct ion on impact with 
water or denser medium pro¬ 
viding it has been dropped 
from sufficient altitudeto 
arm. .crash-proof.. .36" and 
42" extension rods avail¬ 
able with this fuse 

Mk221 

Nose: 

mech. impact 
rotor arm. 

0.01 

165 v. rev 

850-1100 air tr 


500 GP, Mk 12 

1000 GP, Mk 13 

Mk223 

none 

obsolescent, will fit nose 
of all DB's, but delay may 
rupture case....400 ft/sec 
striking velocity is needed 
to activate fuse on water 
impact 

Mk223 

4 mods 

Tail: 

mech. impact 
rotor arm. 

0.01 

approximately 

150 v.rev 

850-1100 air t r 


500 GP, Mk 12 4 mods 

1000 GP, Mk 13 

AN-Mk219 
Mk22 1 
and. . . 

see remarks 

none 

obso1escent..other compan¬ 
ion fuzes:AN-MI03,AI;MI35, 
Al; MI36, Al; AN-MI39 Al; 
AN-M140A1;M149;Mk239;Mk243 

AN-Mk224 

4 mods 

Athwartship 

hyd rostatic 

25,50,75, 

100,125 ft 
of water 

completely armed 
at 12 to 25 ft 
dept h 

- 

All DB's except 

Mk53 and Mk54 

AN—Mk219i 
AN-M103; 
Mk221 and 
Mk229 in 

650 4 7Q0 
DB's 

spacer ring 
required 
with 650 4 
700 DB's 

obsc1escent 

Mk227 
mod 0 

Nose: 

mech.impact, 
cent rifuga 1 
force arm. 

Inst. 

at sea 1 eve 1 : 

1 500 air t r 
20,000' alt: 

3000 air t r 


5 AA bomb, Mk34 

none 

none 

fuse designed for air to 
a i r .bomb i ng, but proved un¬ 
successful ..... 1 i mi ted use 
against parked aircraft 

AH-Mk228 

4 mods 

Tail: 

mech.impact 
rotor arm. 

0.08 

14-0-160 v.rev 
1100 air t r 

200 

1000 AP; 1600 AP; 

1500 GP, Mk 12 mod 2 

1000 GP, Mk13 mod 2) 

none 

none 


Mk229 

4 mods 

Tail: 

hyd rostatic 
mech.arming 

25,50,75, 

100,125 ft 
of water 

1 10 v . rev 

500 air t r 

60 

650 4 700 OB's; 

500 GP, Mk12; 

1000 GP, Mk13 

AN-Mk219 
AN-MI03 
Mk243 

none 

mod 3 preferred in opera¬ 
tional missions for its ad¬ 
ditional safety features 

AN - Mk230 

4 mods 

Tail : 

hyd rostat i c 
mech. armi ng 

25,50,75, 
100,125 ft 
of water 

110 v.rev 

30C-400 air t r 

60 

325 D8,Mk53; 350 DB, 
Mk54; 500,1000,2000 
GP's AN-M64,65,66,4 
mods by removing a- 
dapter from Ml 15 a- 
dapter booster; 650 

4 700 DB's by remov¬ 
ing Mkl bstr pel let 
and inserting 2 Mk2 
booster pellets 

AN-Mk2IQ 

AN-MI03 

Mk243 

- 

mod 1.3 obso 1 escent... mod4 
is preferred for its crash¬ 
proof features.mod5, 

identical to mod4, is con¬ 
verted from Mk229 










Mk231 
mod 0 

Tail : 

hyd rostatic 

Identical to Ml 

— 

25 ft of 
water 

(231 but has lo 

_ 

40-45 v.rev 

nger arming stem 

60 

325 DB,Mk53; 350 DB, 
Mk54; 500 GP,AN-M64,AI 


none 

under development.no 

availability date set.... 
crash-proof and detonator 
safe 

Mk240 


1000 GP, AN-M65,A 1 

2000 GP, AN-M66,A 1 

Mk232 

4 mods 

Nose: 

impact or 
e 1 ec. f i r i ng 

Inst, or 
electr ic 
impulse 

8 v. rev 


GP's, ( SAP's) and DB's 
except 100 GP, Mk4 

usual 1 y 
none 

none 

special purpose fuze... 
will not function on impact 
with water at striking ve¬ 
locity less than 700 ’ft/sec 

Mk233 
mod 0 

Nose : 

e1ec.firing 

electrica1 
impulse 



100 GP,Mk4 



specia 1 purpose fuse. 

1imi ted avai1abi1 i ty 

AN-Mk234 

4 mods 

Athwartsh i p 

hyd rostatic 

25,50,75 
100,125 ft 
of water 

pa rt i a 1 ly armed 
when d ropped... 
completely armed 
at 12 to 25 ft 
dept h 


all DB's except 

Mk53 and Mk54 

AN-MI03 
AN-Mk219 - 
Mk22 1 
Mk229 

spacer ring 
requ i red 
with 650 4 

700 DB’s 

differs from AN-Mk224 in 
that it has external set¬ 
ting device..not air arming 
type; not recommended for 
use. .. .cannot- be installed 
when trunnion band is used 

Mk237 
mod 0 

Tail : 

long delay 

2,10,30 
hrs at 60°F 

approximate 1y 

150 v.rev 
plus impact 


500 GP,AN-M64, Al 

none 

none 

detonator 4 jettison safe 
...anti-remova1 device... 
fuse may function without 
delay on multiple impact., 
minimum safe altitude same 
as for instantaneous fuses 

1000 GP.AN-M65, Al 

2000 GP.AN-M66, Al 

Mk238 
mod 0 

Mk239 
mod 0 

Nose : 

mech.impact 
rotor arm. 

0.01 

1100 air t r 


All GP's(except 100 
GP,Mk 4) 4 SAP's 

Mk223 
for Army 
bombs use 
Army fuzes 


mod i f i ed Mk22 1. .. . requ i res 
400_ft/sec striking velo¬ 
city to function on impact 
with water 

Mk243 
mod 0 

Nose : 

mech.impact 

0.025 

130 v.rev 

500 air t r 


All GP's(except 100 

GP, Mk4 ) and SAP's 

AN-MI00 

series 

AN-Mk230 

Mk229 

Ml 4 

pri mer-det 

designed specifically for 
use against submarines and 

ships. will function on 

impact with 4" plate, but 
not with waiter from altitude 
of 15,000 ft or at impact 
angle of less than 45° 



363 
































































































WEAPON DATA 

PHYSICAL CHARACTERISTICS OF AMERICAN BOMBS 


I A5a * 

AMERICAN 

L HIGH EXPLOSIVE BOMB^ 



TOTAL 

TYPE OF 

WEIGHT OF 

CHARGE 

MAX. 

LENGTH OF 

WALL 


DESIGNATION 

WEIGHT 

CHARGE 

CHARG 

E ,[b 

WEIGHT 

BODY 

BOMB 

,tn 

THICK- 

REMARKS 


W, Lb 


w 

w L/ 3 

RATIO 

DIA. 

WITHOUT 

OVER 

NESS 







w/W 

in 

TAIL 

ALL 

i n 



GENERAL PURPOSE BOMBS 


*IOO-1b GP, 

Mk1 4 Mods 

1 16 

TNT 

65 

4.0 

56 

7.9 


48.8 


Bomb has teardrop shape 

Mk4 Mod 1 

120 

TNT 

55 

3.8 

46 

8.0 

28.0 

36.2 

0.18 

Single piece stee1 
forging, cylindrical 
with ogival nose. 

Mk4 Mod 4 

105 

TNT 

55 

3.8 

52 

*500-lb GP, Mk 1 2 Mod 2 

504 

TNT 

256 

6.4 

51 

14.0 

42.6 

59.5 

0.36 

Sling we 1ded to bomb 
for suspension in 
torpedo racks 

1000-1b GP, Mk 13 Mod 2 

1005 

TNT 

51 1 

8.0 

51 

17.7 

53.0 

72.6 

0.45 

100-lb GP, AN-M30;A 1 

1 10 

115 

121 

Amatol 

TNT 

Tritonal 

54 

57 

63 

3.8 

3.9 
4.0 

49 

50 
• 52 

8.2 

29.0 

36.0 

0.16 

Al models may have 
anti-withdrawa 1 fuze. 
T'hese bombs may have 
parachute attachment 

M6 to prevent rapid 
descent and ricochet 

of bombs in low-level 
bombing 

250-1b GP, AN-M57;A 1 

256 

260 

273 

Amatol 

TNT 

Tr itonal 

124 

129 

142 

5.0 

5.1 

5.2 

48 

50 

52 

10.9 

36.0 

45.4 

0.27 

500-lb GP, AN-M43 

AN-M64;A 1 

510 

525 

535 

544 

Amatol 

TNT 

Comp. B 

Tritonal 

262 

267 

274 

293 

6.4 

6.4 

6.5 

6 .6 

51 

51 

51 

54 

14.2 

45.0 

56.8 

0.3 

500-lb AN-M43 and 

AN-M64;AI may have 
parachute attachment 

M7 to prevent rapid 
descent and ricochet 

of bombs in lowlevel 
bombing. A 1 mode 1s may 
use anti-withdrawa1 
fuze; baseplates and 
adapter boosters can¬ 
not be removed.AN-M64, 
65, 66 &A 1 mode 1 s hav e 
tai 1 fuze pockets tak¬ 
ing hydrostatic fuze 
AN-M230 ( 1 1.5-1 bs heav- 
i er than AN-MI00 ser¬ 
ies fuzes). AN-M66A2 
has slightly heavier 
nose section. 

1000-lb GP, AN-M44 
AN-M65;A1 

964 

990 

1040 

1044 

Amatol 

TNT 
Comp. B 

Tritonal 

530 

558 

595 

612 

8.1 

8.2 

8.4 

8.5 

55 

56 

57 

59 

18.8 

53.1 

67.1 

0.5 

2000-lb GP, AN-M34 
AN-M66;A 1 
AN-M66 A2 

2050 

2105 

2140 

2212 

Amatol 

TNT 

Comp. B 

Tr itonal 

1063 

1 117 
1142 
1220 

10.2 

10.4 

10.5 
10.7 

52 

53 

53 

55 

23.3 

70.0 

90.4 

0.5 

4000-lb GP, T8 

4084 

4229 

TNT 

Tritonal 

1857 

2002 

12.3 

12.6 

45 

47 

28.0 

86.5 

118.9 

0.88 

12000-lb GP, TIO 

1 1750 

Tr i tonal 

5100 

17.2 

43 

38 

124 

252 

1 .25 

1 ne rt i a tail fuzes. 
For performance see 
Data Sheet 7A1. Re - 
spectively same as 
British "Tallboy-M" 
and "Grand Slam",but 
British mode Is fi1 led 
Torpex D-1 

22000-lb GP, T14 

22115 

Tritonal 

9440 

21.3 

43 

46 

150 

305 

1.75 

LIGHT CASE BOMBS 

4000-lb LC, AN-M56;AI 

4232 

4205 

4531 

Amatol 

TNT 

Tr i tonal 

3238 

3362 

3690 

14.8 

15.0 

15.5 

77 

80 

81 

34.0 

94.9 

117.3 

0.37 

A 1 mode 1s have hoisting 
at center of gravity 
as well as provision 
for suspension in Bri¬ 
tish pianes. 


SEMI ARMOR-PIERCIPG POMPS 


500-lb SAP, 

AN-M58 

4 72 

TNT 

160 

5.4 

34 

11.8 

46.8 

57.8 

0.75 

. ■ - ■"-== 

A2 mods may use anti- 
withdrawal fuzes. 

AN-M58A1,A2 

494 

TNT 

162 

5.5 

33 

1000-lb SAP, AN-M59;A1 

995 

TNT 

320 

6.8 

32 

15.1 

57.3 

69.3 

1.0 

Al mod may use anti- 

withdrawa1 fuzes. 

Solid nose construc- 
t i on 

2000-lb SAP, M103 

2040 

Picratol 

556 

8.2 

27 

18.7 

67.7 

88.5 



ARMOR-PIERCING BOMBS 


1000-lb AP, AN-Mk33 

1025 

Explosive D 

140 

5.2 

14 

12.0 

58.0 

73.0 


:i 

1600-lb AP, AN-Mkl 

1590 

Explosive D 

215 

6.0 

14 

14.0 

59.5 

83.5 

1.3 

Recent bombs have 

grooves on body to 
position suspension 
band 

ANTI-AIRCRAFT BOMBS 


j 5-lb AA, Mk34 

5.5 

TNT 

1.9 

1.2 

35 

3.0 

12.0 

15.0 

0.05 

Cluster of 20 bombs 

in Mk3 or Mk3 Mod 1 
containe r 


ObsoIescent 


Rev i sed : 
August 1945 





































































































































PHYSICAL CHARACTERISTICS OF AMERICAN BOMBS 

continued 


DESIGNATION 

TOTAL 

WEIGHT 

W, lb 

TYPE OF 
CHARGE 

WEIGH1 

CHARGE 

OF 

.lb 

CHARGE 
WEIGHT 
RATIO 
w/W % 

MAX. 

BODY 

DIA. 

1 n 

LENGTF 

BOMB. 

OF 

1 n 

WALL 

THICK- 

NESS, 

in 

REMARKS 

w 

1/3 

W 

WITHOUT 

TAIL 

OVERALL 

FRAGMENTATION BOMBS 

.Adaptation of German 

4-1b F, M83 (Butterfly) 

3.2 

TNT 

0.47 

0.77 

15 

3.0 

3.0 


0.25 

SD-2; dropped inclus- 
te rs 

23-lb F, AN-M40;A 1 

M72;A1 

20** 

TNT 

2.7 

1.4 

14 

3.6 

1 1.3 

26.7 

0.56 

Bombs dropped in clus¬ 
ters. M72 is modified 
version of AN-M40 

adapted for vertical 
suspension. Al mods 
faci 1 itateclustering 
with fuzed bombs 

20-lb F, AN-M41;A1 

20 

TNT 

2.7 

1.4 

14 

3.6 

1 1 .3 

19.5 

0.56 

Des igned also forver- 
tical suspension,may I 
bedropped incluster 

0 f 6 bombs. Al mods 
faci1itate clustering 
with fuzed bombs 

90-lb F, M82 

90 

Comp. B 

1 1 

2.2 

12 

6.0 

19.8 

28.0 

0.94 

Suspended by single 
lug or in cl ust er of 

6 bombs 

120-1 bF, M86 (Para) 

90** 

Comp. B 

11 

2.2 

12 

6.0 

19.8 

55.3 

0.94 

May be suspended sing¬ 
ly or in a two-bomb 
cluster in a 500-lb 
bomb station 

220-lb F, M88 

260-lb F, AN-M8I 

216 

260 

Comp. B 
Comp. B 

47 

34 

3.6 

3.2 

22 

13 

8.0 

8.0 

32.8 

32.8 

43.7 

43.6 

1.00 

1.25 

Horizontal suspension 
helical steel spring 
wound around steel 
tubing 


FRAGMENTATION CLUSTERS 


DESIGNATION 

CLUSTER 

FUZING 

TOTAL 

WEIGHT 

pounds 

MAX. BODY 
DIAMETER 

inches 

OVERALL 

LENGTH 

inches 

REMARKS 

100-1b Ml or AN-MIAI 

6-20 lb F, AN-M4I 


125 

8.8 

46.6 

Fuzes shipped installed. Use cluster adapter 

AN-MIA2 

100-lb AN-MIA2 

6-20 lb F, AN-M4IAI 


125 

8.8 

46.6 

Fuzes shipped in sealed cans; installed in the 
field. Use cluster adapter AN-MIA3 

100-lb SIZBL 

6-20 lb F, AN-M4I 


125 

8.8 

46.6 

Navy designation. Use cluster adapter AN-MIA2. 

100-lb AN-M4 

3-23 lb F, AN-M40 


87.2 

1 1 

31 .0 

Use cluster adapter AN-M3. Fuzes shipped in- 
sta11ed 

100-lb AN-M4AI, A2 

3-23 lb F, AN-M40;A1 


87.2 

1 1 

31.0 

Fuzes shipped in sealed cans; installed in 
field. Use cluster adapter AN-M3, Al. 

1 00-lb M28, M28A 1 ,A2 

24 - 4-lb F, M83 

Ml 1 IA2 

M146 

Ml 55 

155 

8.0 

47.3 

Should be released from altitude of 3000-5000 
feet with fuze set to function 5IM28) & 8(M29) 
sec. after release, to form a pattern of approx . 
200x300 feet.. Use MI5,AI,A2 adapters for M28,AI, 
A2; use MI6,AI, A2 for M29, Al. 

500-lb M29, M29AI 

90-4 lb F, M83 

415 

14 

59.6 

500-lb M26, M26AI ,A2 

20-20 lb F, AN—M41;A 1 

Ml 1 IA2 

M146 

Ml 55 

T77 

415 

15 

53.5 

Use cluster adapter MI3,A|,A2; can have quick 
or delayed opening 

500-1b M27 

6-90 1 b F , M82 

Ml 1 IA2 

Ml 46 

Ml 55 

590 

15 

59.0 

Use cluster adapter MI4. Has inst. and 5-92 
second delay 


‘Obsolescent “Weight without parachute 

NOTES: 


Bomb weight given includes weight of standard Army - Navy fuzes, 
AN-MI03 (nose) and AN-MIOO (tail); due to slight variations in 
case thickness and density of fiI Iing,weights are accurate to*5%. 

The designation Amatol, above, implies a fiI Iing of 50 % Amm.Nitr.i 
50% TNT; TNT represents 100% TNT; Tritonal signifies 80% TNT ana 
20% Aluminum. Tritonal has been approved as the main charge in GP 
and LC bombs which are to be used where those Ioaded TNT we re for¬ 
merly considered suitable. The charge weights of tritonal - filled 
bombs listed above were calculated using a density of 1.70 fortri¬ 
tonal as compared with 1.55 for TNT. 

For Bomb-Fuze combinations, see Weapon Data Sheet I A3. 


Abbreviations: 

BOMB TYPE, U. S. BRITISH APPROXIMATE 

DESIGNATION CHARGE-WEIGHT RATIO 


General Purpose, GP 

MC 

50% 

Light Case, LC 

HC 

80% 

Semi-Armor-Piercing, SAP 

GP 

30% 

Armor Piercing, AP 

AP 

15% 


Fragmentation, F 
Anti-Airc raft, AA 


SOURCE: Information supplied by the United States Navy Bomb Disposal School. 






































































WEAPON DATA: INCENDIARIES 

PHYSICAL CHARACTERISTICS 
OF AMERICAN INCENDIARY BOMBS 


-\ 



INCENDIARY BOMBS 


DESIGNATION 

nominal 

weight model no. 

ACTUAL 

WEIGHT 

pounds 

DIMENSIONS. 

INCENDIARY 

CHARGE 

OTHER 

CHARGES 

TOTAL HEAT 
LIBERATED 

BTU 

FUSING 

type 6 
number 

STRIKING 

VELOCITY 

from20,00O(t 

feet/sec 

CLUSTER SIZES 
AND TYPES 

DIAM 

inches 

LENGTH 

inches 

100-lb. AN-M47A2 
AN-M47A3 

72* 

73* 

8.12 

8.12 

48.9 

51.9 

401b. Gasoline 

Gel 

M12 Burster: 

Black Powder 7.8 oz. 
Mg. Powder 7.4 oz. 
M13' M9,Burster- Igniter 
W.R-2loz.,TNT-2.4«, 
Tetryl- 0.07 oz. 

669,000 

(includes heat 
of White Phos) 

Nose 

Impoct 

M-I26AI 

or 

M-108 

740 

Not clustered but 
sometimes loaded by 
multiple suspension 
on 100-lb. and 500-lb 
stations 

4-lb AN-M50A2 

3.6 

1.69 

21.3 

l.l lb Mag alloy 
0.61b Therm-64C 

First Fire*0.7l oz. 

13,100 

Toil 

Inertia 

420 

500-lb size, Aimable 
100-lb size, 1 Quick- 
500- lb size,)Opening 

4-lb AN-M50XA3 
(anti-personnel 
explosive nose) 

3.7 

1.69 

21.3 

1.05 lb Mag. alloy 
0.61b Therm-64C 

First Fire* 0.71 oz. 

Tetryl (type A) l.4oz 
Tetryl (type B)l.6oz 

12,300 

Tail 

Inertia 

425 

Clustered with 
AN-M50A2 

2-lb AN-M52AI** 

1.7 

1.69 

14.2 

0.95 lb Mag. alloy 
05 lb Therm-64C 

First Fire* 0.7oz. 

11,200 

Tail 

Inertia 

340 

500-lb size, Aimable 
100-lb size,) Quick- 
500-lbsize,) Opening 

4-lb AN-M54 

3.7 

1.69 

21.3 

1.6 lb Thermate 

First Fire* 0.7oz. 

2,600 

Tail 

Inertia 

420 

100-lb size,! Quick- 
500-lb size,)Opening 

6-lb AN-M69** 

6.2 

2.87 

ia5 

2.6 lb Gasoline 
Gel 

Black Powder 0.27oz 
Mag. Powder 0.23oz 

44,000 

Nose 

Inertio; 

M 1 

230 

500-lb size, Aimable 

100-lb size, 1 Quick - 
500-lb size,! Opening 

6-lb M69X 
(anti-personnel 
explosive nose) 

7.0 

2.87 

ia5 

2.21b Gasoline 
Gel 

Black Powder 0.27oz 
Mag.Powder 0.23oz 
Tetryl 4.6oz 

37,000 

Nose 

Inertia; 

M 1 

245 

Clustered with 

AN-M69 

10-lb M74 

8.4 

2.87 

19.5 

2.81b PT-I 
mixture 

White Phos. 6.0oz 
Mag. Powder 0.1 loz 
Black Powder 0.07oz 

38,000 

(includes heot 
of white Phos) 

Nose 
Inertia; 

M142 

420 

500-lb size, Aimable 
100-lb size,l Quick - 
500-lb size,) Opening 

500-lb AN-M76 

475 

14.18 

59.2 

1751b PT-I 
mixture 

Tetryl 1.2 lbs. 

White Phos. 9.0 lb 

2,210000 
(includes heat 
of white Phos) 

Nose Impact 
AN-MI03 
Tail Inertia 
AN-MIOIA2 

965 

Not clustered 
































AN-M69 and M74 are tail ejection type bombs - explosive charge throws incendiary material out of the 
tail. Other gasoline gel filled bombs are burster types which disperse the incendiary material in 
chunks in all directions. 

From time of impact until explosion of head, AN-M50XA3 Type A burns 2-4 min; Type B burns 60-70 sec. 

* First Fire is the agent for initiating- combustion of main filling. 

** Several redesigns of this bomb are now under consideration for standardization. 

+ Weight given is for this bomb with M13-M9 burster-igniter and.M126Al fuse. The 1412 burster weighs 
3 pounds less than the M13-M9 burster-igniter; the M108 fuse, 0.5 pounds less than M126A1 fuse. 

+* New type AN-M69 in production has gross weight of 6.4 lb. and contains 2.2 lb. of gasoline gel, 
6.0 oz. of white phosphorus and liberates 41,000 BTU. 


December 1944 





























WEAPON DATA: INCENDIARIES 

PHYSICAL CHARACTERISTICS 

OF AMERICAN INCENDIARY BOMB CLUSTERS 



V7>e 


a 

AMERICAN 
INCENDIARY CLUSTERS 


'bomb type 

model no. 
nomina1 wt. 

CLUSTER DESIGNATION 

nominal model type 

siz e,lb number 

ACTUAL 

WEIGHT 

★ 

pounds 

NUMBER 
OF BOMBS 

★ A 

TOTAL HEAT 
PER CLUSTER 

BTU 

DISPERSION PATTERN* 

FUSING 

position 
and model 

BOMBING 

TABLE 

8 T: 

A A 

RACE-TRACK 

Sq.ft/Bomb 
(90% of bombs) 

AN-M50 
(4 lb) 

500-lb, AN-MI7AI Aimable 
100 -lb, AN-M6 1 Ouick- 

500-lb, AN-M7 J opening 

465 

135 

525 

110 

34 

128 

1,420,000 
440,000 

1 ,660,000 

420 x 630 
700 x 2450 
700 x 2450 

2,300 

53,000 

14,000 

Nose: MI45® 
Q.0:no fuse 
Q.0:no fuse 

500-J-2 

4-B-l 

4-B- 1 



















AN-M52 
(2 lb) 

100-lb, AN-MI0 1 Quick- 
500- lb, AN-MI1 J opening 

105 

425 

51 

192 

570,000 

2 ,150,000 

1100 x 3300 

1lOOx 3300 

75,000 

20,000 

Q.0: no fuse 
Q.0:no fuse 

2-A-l 

2-A-l 



















AN-M69 
(6 lb) 

500-lb, M18(E6R2) Aimable 
500-lb, E46 Aimable 

100 -lb, AN-MI2 1 Quick- 

500-1b, AN-MI3 I opening 

350 

425 

105 

4 25 

38 

38 

14 

60 

1,670,000 
1,670,000 
620,000 
2,640,000 

340 x 510 
240x 360 
400 x 1000 
400 x 1000 

4,300 

2,200 

29,000 

6,800 

Nose: Ml45® 
Ta i 1:2-M1 bf 
Q.0:no fuse 
0 .0:no fuse 

500-K-2 

500-Q-l 

6-A-2 

6-A-2 



















M 74 
(10 lb) 

500-1b, E48 A imable 

100 -lb, E64 1 Quick- 

500-lb, E57 J opening 

525 

140 

550 

38 

14 

60 

1,440,000 
530,000 
2,280,000 

640 x 960 

15,400 

Tail:2-MI 52® 






























NOTES 

* Weights may vary as much as 5% from average values given. 

**A11 incendiary clusters are supposed to contain 20% of corresponding X-bomb (anti-personnel type), but the percentage 
may vary with supply and operational requirements. 

a Patterns given include 90% of the bombs and are for quick-opening clusters dropped from 10,000 feet and for aimable 
clusters dropped from 20,000 feet and opened at 5,000 feet. Data on quick-opening clusters are less reliable than 
those on aimable clusters. 

aa A race-track figure (rectangle with semi-circular ends) was selected as the most suitable figure for representing the 
patterns of aimable and quick-opening clusters (better than ellipse, rectangle, circle or square). The area of a race¬ 
track is given by xy - 0.215 x 2 , where x = the smaller dimension. In determining dimensions of 90% pattern, axial ratios 
•used were restricted to 1.5, 2.0, 2.5, 3.0, 3.5, 4.0. 

® Ml 45 (T55 EI), M138 (T39EI), and M127 (T39) are alternate fuses for these clusters; M145 preferred. 

® M152 (T53EI), M153 (T73) and M145 (with reversed vanes) are alternate fuses for these clusters; M|52 preferred. 


February 1945 



367 




































WEAPON DATA 

PHYSICAL CHARACTERISTICS OF AMERICAN 
DEPTH BOMBS, AIRCRAFT MINES AND TORPEDOES 


I A 7 ) cl 

JL AMERICAN BOMBS 
MINES AND TORPEDOES 


DESIGNATION 

nominal 

weight model 

TOTAL 

WEIGHT 

W 

lbs 

TYPE 

OF 

CHARGE 

WEIGHTof CHARGE 
pounds 

CHARGE 
WEIGHT 
RATIO 
w/W, % 

DIMENSIONS 

DIAM 

inches 

WALL 

THICK¬ 

NESS 

inches 

FUSING 

LENGTH 

OVERALL 

inches 

LENGTH 
of Bocnr 
inches 

NOSE 

ATHWART 

SHIP 

TAIL 

w 

w b 

A depth BOMBS 

325-lb AN-Mkl7-2 
350-lb AN-Mk44 

323 

355 

TNT 

TPX 

242 

268 

6.23 

6.45 

75 

76 

52.5 

31.1 

15.0 

0.06 

(AN-Mk219 

(AN-Mk221 

AN-Uk23A 

AN-Mk224 


325-lb AN-Mk41 
350-lb AN-Mk47 

325 

351 

TNT 

TPX 

222 

248 

6.06 

6.28 

68 

71 

49.9 

27.8 

15.0 

0.06 

(AN-LA103 
(AN-kk219 
(AN-Mk221 

AN-iik224 

AN-Mk234 

- 

325-lb Mk53-1 

350-lb Mk54-1 * 

320 

339 

TNT 

TPX 

225 

252 

6.08 

6.32 

70 

74 

54.6 

30.1 

13.5 

0.06 

(AN-M103 

(AN-Mk219 

- 

jAN-kk230 

650-lb Mk37 ** 
Mk38-1 
700-lb Mk49-1 

635 

634 

669 

TNT 

TNT 

HBX 

464 

425 

472 

7.74 

7.52 

7.79 

73 

67 

71 

58.5 

36.4 

17.7 

0.12 

/AN-Mk219 
[AN-M103 

AN-Mk224® 

AN-Wk231* 

Mk229 * 

) 

^AN-Mk230 














]> AIRCRAFT MINES 

1000-lb,Mkl3-0,4,5 

1025 

TNT 

621 

8.53 

- 

68.8 

- 

19.9 

0.12 

m0,4: Mag.Indue.Type 
m5: Acoustic Type 

1000-lb,Mk26-l 

1000 

1060 

TNT 

TPX 

465 

525 

7.75 

8.07 

- 

68.5 

- 

18.6 

0.12 

Magnetic Induction 

Type 

1000-lb,Mk36 

1020 

1085 

TNT 

TPX 

570 

635 

8.29 

8.59 

- 

70.6 

- 

18.6 

0.12 

Magnetic Induction 

Type 

1600-lb Mkl2-1 | 

4 I 

1595 

1725 

1565 

1690 

TNT 

TPX 

TNT 

TPX 

1095 

1225 

1065 

1190 

10.3 

10.7 

10.2 

10.6 

- 

134 

134 

- 

20.8 

20.8 

0.25 

0.25 

Magnetic Needle Type 

Magnetic Needle Type 

1800-lb,Mkl0-6,8,9 

1850 

TNI 

420 

7.49 

- 

121.5 

- 

20.8 

0.25 

Magnetic Needle Type 

2000-lb,Mk25 

1863 

2017 

TNT 

TPX 

1120 

1274 

10.38 

10.84 

- 

86.5 

- 

22.5 

0.15 

Magnetic Induction 

Type 












{) AIRCRAFT TORPEDOES 

Mk 13-2A, 3, 5 

Mk 13-6, 7, 9 

2140 ® 
2228® 

TNT 

TPX 

600 

600 

8.43 

8.43 

- 

161.0 

- 

22.4 

0.12 

Contact: Mk4-6 

Mk8-6 













NOTES: 

*.This Depth Bomb is currently being filled with HBX instead of Torpex (TPX). 

** Because the tail assembly was too weak, the Mk37 was revised producing the Mk38. 
e In this group, these fuses are used in the 650-lb Mk37 D.B. only; the Mk38 and Mk49 do not use an 
athwart-ship or side fuse. 

x The Mk229 fuse is vised only in the Mk37 D.B.; the newer depth bombs, Mk38 and Mk49, use the AN-Mk230. 
o The total weight may vary as much as i 20 pounds from the weight given. 

General Purpose bombs (GP 500-lb AN-M64, 1000-lb AN-M65, 2000-lb AN-M66) fitted with the AN-Mk230 hydro¬ 
static tail fuse are also used as depth bombs. 

Since Aircraft Mines are usually dropped by parachute, the over all length dimension is given includ - 
ing the parachute pack; without it this dimension is approximately 4 inches less. 

SOURCE: Publications of the Bureau of Ordnance and the Bomb Disposal School, U.S.Navy. 


PTM No. 97 December 1944 


368 


CONFIDEN 












































































WEAPON DATA 


PHYSICAL CHARACTERISTICS OF BRITISH BOMBS 


4 4 a 


1 - 

PHYSICAL 
CHARACTERISTICS 


A HIGH EXPLOSIVE BOMBS 


DESIGNATION 

name,type and model 

TOTAL 

WEIGHT- 

pounds 

TYPE Of 
CHARGE 

WEIGHTof 

CHARGE 

pounds 

CHARGE" 
WEIGHT RATIO 

percent 

MAX. BODY 
DIAMETER 

inches 

LENGTH 
without TAIL 

inches 

OVERALL 

LENGTH 

inches 

BODY WALL 
THICKNESS 

inches 

20-lb. F., MklE 

20 

TNT 

3 

15 

3.9 

11.9 

21.8 

0.35 

40-lb. G. P, MkEL 

38.5 

Amotol 60/40 

6.5 

17 

5.0 

15.9 

27.3 

0.47 

250-lb. G. P., MkEZ 

230 

Amotol 60/40 

67 

29 

10.3 

25.6 

55.7 

0.52 

500-lb. G.P., MkEZ - 

470 

Amatol 60/40 

143 

30 

13 X) 

36.5 

70.3 

0.72 

500-lb. G.P., MkEZ 

467 

Amatol 60/40 

143 

31 

13.0 

36.5 

57.3 

0.72 

1000-lb. G.P.,Mk II 

1072 

Amato 160/40 

357 

33 

16.2 

52.5 

72.5 

0.77 

1900-lb. G. P.,MkE 

1785 

Amatol 60/40 

470 

26 

18.5 

65.5 

101.0 

1.15 

4000-lb. G.P^MkiaH 

3587 

Amotol 60/40 

1072 

30 

24.5 

81.0 

106.0 

1.35 

250- lb. S.A.P., Mk3£ 

245 

TNT 

42 

17 

9.2 

31.5 

42.2 

0.91 - 0.99 

500-lb. S.A.P., Mk3£ 

490 

TNT 

89 

18 

11.5 

41.8 

62.0 

1.22—1.32 

500-lb. S.A.P., Mk3T 

483 

TNT 

89 

19 

11.5 

41.8 

52.0 

1.22-1.32 

2000-lb.A.P., MklE 

1934 

Shellite 

166 

9 

13.5 

80.0 

113.0 


100- lb. A.S.,Mkl2 

98 

TNT 

44 

45 

8.0 

25.0 

42.0 

O.ll 

250-lb. A.S.,MkIE 

243 

TNT 

134 

55 

11.3 

36.0 

58.0 

0.14 

500-lb A.S.,MkEZ 

490 

TNT 

282 

58 

14.3 

50.0 

73.5 

0.18 

500-lb. M.C.,Mk l&E 

447 

Amatol 60/40 

224 

50 

12.9 

42.0 

70.6 

0.3 

500-lb. M.C.,Mkiai 

4 39 

Amatol 60/40 

224 

51 

12.9 

42.0 

57.8 

0.3 

500 -lb. M.C.,MkIE 

5 10 

Amatol 60/40 

210 

41 

12.9 

42.0 

70.6 

0.42 

500-lb. M.C.,MkHI 

502 

Amotol 60/40 

2 10 

42 

12.9 

42.0 

57.8 

0.42 

500-lb. M.C., MkDZ 

440 

Amotol 60/40 

174 

40 

12.9 

36.5 

70.3 

0.42 

500-lb M.C^MkBZl 

437 

Amotol 60/40 

174 

40 

12.9 

36.5 

57.3 

0.42 

500-lb. M.C.,Mk3L 

510 

Amatol 60/40 

210 

41 

12.9 

42.0 

70.6 

0.42 

1000-lb. M.C,MkI 

102 1 

Amatol 60/40 

475 

47 

17.5 

52.5 

72.5 

0.42 

4000-lb. M.C.,Mk I 


Amatol 50/50 
Amatol 60/40 
Amatol 60/40- 
f ine groined 
Amotex9 
RDX/TNT 


55 

30.0 

74.5 

109.5 

0.75 

2000-lb.H.C., Mk I 

1842 

Amatol 60/40 

1340 

73 

18.5 

99.5 

162.0 

0.19 

2000-lb. H.C., MkiranL 

1723 

Amotol 60/40 

1230 

71 

105 

89.0 

131.0 

0.19 

4ooo-ib. ho, Mkmaisr 

3944 

Amatol 60/40 

2960 

75 

30.0 

82.0 

110.0 

0.31 

8000 -lb. H.C.,Mk I an 

7860 

Amotol 60/40 

5361 

68 

38.0 

nose 47.2 
rear 47.8 

133.0 

0.50 

12000-lb. H.C. 

11800 

Amatex 9 

7800 

66 

380 


180.0 



ABBREVIATIONS 



AMERICAN 

EQUIVALENTS 

GERMAN 

EQUIVALENTS 

M.C. 

MEDIUM CHARGE, charge-weight ratio about 

50% 

G.P 

S.C. 

H.C. 

HEAVY CHARGE , charge - weight rotio about 

70-75% 

L.C. 


G.P. 

GENERAL PURPOSE,charge-weight ratio about 

30% 

SAP. 

SD. 

A.P. 

ARMOR PIERCING, charge-weight ratio obout 

5-8% 

A.P. 


S.A.P. 

SEMI-ARMOR PIERCING, chg-wt ratio about 

18% 


PC. 

A.S. 

ANTI-SUBMARINE 




F. 

FRAGMENTATION, anti-personnel 




NOTE: COMPILED from 

DATA SUPPLIED BY THE BRITISH MINISTRY OF SUPPLY 





December 1943 



369 






































































WEAPON DATA 

PHYSICAL CHARACTERISTICS 
OF GERMAN BOMBS AND MINES 


A HIGH EXPLOSIVE BOMBS 


TYPE 

TOTAL 

WEIGHT- 

pounds 

TYPE of 
CHARGE 

WEIGHTof 

CHARGE 

pounds 

CHARGE- 
WEIGHT RATIO 
percent 

MAX. BODY 
DIAMETER 

inches 

LENGTH 
without TAIL 

inches 

BODY WALL 
THICKNESS 

inches 

NOSE 

CORRECTION 

inches 

2 kg. S.D.2 
Anti-personnel 
"Butterfly " 

4.4 

TNT -cast 

75 oz 

1 1 

3.0 

3.1 

3/ 8 


12-kg. S.C. 10 
Anti-personnel 

26 

TNT 

2.0 

7.7 

3.25 

15 

0.5 

30-35-kg. S.Be50 
Anti-personnel 

66-77 

TNT 

15 


7.0 

27 

1.7 5 


10-kg. B.D.C. 









50-kg. S.C. 

1 1 3 

TN Tor Amatol 

53.7 

48 

8.0 

28-31 

3/16 

3.83 

50-kg. S.D. 

1 1 3 

TNT 

36.1 

32 

8.0 

23.5 

3/8 

3.83 

70-kg. S.C. 

154 

TNT 

46.2 

30 

8.0 

28-31 

0.39 


100-kg. S.C. 

220 


NO 

50 

10 

33 

5/32 


250-kg. S.C. 

519 

TNTor Amatol 

2 86 

55 

14.5 

46.5 or 47.0 

9/32 or 5/16 

6.80 

250-kg. S.D. 

528 

TNT 

1 74 

33 

14.5 

36.0 

7/8 

6.80 

500-kg. S.C 

1 120 

TNTorAmatol 

4 84 

43 

18, l8.5orl9 

60,52or 545 

’ reso 

9/32 or 5/16 

9.39 

500-kg. S.D. 

1087 

1 100 

TNT/wax 
TNT-cast 

1 65 

1 65 

1 5 

15 

15.6 

15.0 

54.0 

32.5 

0.9 

1 .6 

8.35 

8.35 

500-kg. S.D. 

1 190 

TNT 

420 

35 

17.5 

54 

1 .19 


500-kg. P.C. 

Rocket Bomb 

1 100 

TNT-cast 

220 

20 

15.6 

42.7-54.0 



1000-kg.S.C. 

"Hermann" 

2200 

2400 

TNT- cast 8 
granulated 

11 90 

54 

50 

26.2 

75.0 

3/8 

1 2.57 

1000-kg.S.C. 

2070 ? 





65 ? 



1000-kg. S.D. 

II __ M 

Esau 

2240 

TNT/wax 

319 

1 4 

19.8 

57.8 

1 .38 


1000-kg. PC. 
Rocket Bomb 

2200 

TNT-cast 

308 

14 

19.8 

58.0 


1 1 .72 

lOOO-kg.R.S.-P.C. 

2200 


121 

5.5 

15.5 

47.0 



1200-kg. S.C. 

2640 


1590 

60 

26.2 

74.0 



1400-kg. S.D- 
Fritz 

3010 

TNT/wox 

660 

22 

22.0 

75.0 

1.5 


1400-kg. PC. 

3080 


660 

21 

21.9 

76.5 


1 2 .06 

1700-kg. SC.D. 

3760 

TNT-cast 

1630 

43 

25.5 

92.0 

15/16 

1 1 .73 

1730-kg. S.C. 

" Moorhead " 

3810 


1600 

42 

25.5 

91.5 

1.0 


1800-kg. S.C. 
Satan 

3900 

TNT or Amatol 

2100 

54 

25.9 

104 

0.4 

1 3.72 

1800- kg.R.S.-P.C. 

3960 


374 

9.4 





2500-kg.S.C. 

H . . ii 

Max 

5500 

TNT 


Excessive 
(80 9) 

30-31 





A 5 a 


i- 

PHYSICA L 
CHARACTERISTICS 



ABBREVIATIONS 

S. C. (SPRENGCYLINDRISCH) THIN WALLED, GENERAL PURPOSE.. ..CHARGE-WEIGHT RATIO APPROXIMATELY 
50%. USED PRIMARILY FOR GENERAL DEMOLITION....MAIN FILLING USUALLY TNT OR AMATOL. 

S . D. (SPRENGDICKENWAND) THICK WALLED,SEMI-ARMOR- PIERCING OR ARMOR-PIERCING ... CHARGE-WEIGHT 
RATIO APPROXIMATELY 30%.... USED PRIMARILY AGAINST SHIPS AND FORTIFICATIONS.. CO NT AI N TNT 
PELLETS COATED WITH LIGNITE WAX TO REDUCE THE SENSITIVITY OF THE EXPLOSIVE. 


P. C. ARMOR-PIERCING....CHARGE-WEIGHT RATIO APPROXIMATELY 20%. 


ALL BOMBS LARGER THAN THE 50-kg. HAVE A COLUMN OF TNT PELLETS WR APPED IN PAPER AND EXTEND I NG 
THROUGH THE CENTER OF THE BOMB TO INSURE HIGH-ORDER EXPLOSION. 

COMPILED FROM DATA IN THE U.S . WAR DEPARTMENT TECHNICAL MANU AL , TM-E9 -1983 
AND FROM DATA SUPPLIED BYTHE BRITISH MINISTRY OF HOME SECURITY 


August 1943 


































































WEAPON DATA 

PHYSICAL CHARACTERISTICS 

OF GERMAN BOMBS AND MINES (continued) 


FI A!iir 

M. PHYSICAL 
CHARACTERISTICS 

l -/ 


1> INCENDIARY BOMBS 


TYPE 

TOTAL 

WEIGHT 

pounds 

TYPE of 
CHARGE 

WEIGHT of 

CHARGE 

pounds 

CHARGE- 
WEIGHT RATIO 
percent 

MAX. BODY 
DIAMETER 
inches 

LENGTH 
WITHOUT TAIL 
inches 

BODY WALL 
THICKNESS 
inches 

B 1 - kg. EL 

2.03 

Thermite 

0.44 


1.97 

9.64 

25/64 

B 1 - kg. El. plus 
explosive chorge 

2.03 

Thermite 

TNT 

0.44 

0.016 


1.97 

9.64 

25/64 

B 1.3-kg. St eel Nose 

2.78 

Thermite 

0.44 


1.97 

9.64 

25/64 

B 2.2-kg.El-2(IBEN) 
Incend.&anti-Derson’l 

4 Ib.-I4oz. 

Thermite 

TNT (in nose) 

0.56 

0.37 


lncend.1.96 
Nose 1.78 

16.8 

Incend. 25/64 
Nose 1/4 

50-kg. Thermite 
Incendiary 

75.0 

Thermite 

TNT 

20.0 


8.0 

28.0 

0.15 

50-kg. 

Phosphorus 

Incendiary 

90.0 

Benzine 86% 
Phosphorus4% 
Rubber 10% 

30.0 

33 

8.0 

30.0 

1/8 

50-kg. Sb. C 

no 


16-17 

15 


28.3 - 30.3 


IIO-kg. (Flam) 
Incendiary 

242 

Gasoline 

TNT 

110 

45 

14.5 

40.0 

1/16 

250-kg. (Flam) 
Incendiary 

550 

Gasoline 

TNT 



18.0 

62.0 

1/16 

ABB 500 (152-kg.) 
Incendiary Container 

336.0 

120 1-kg. 
Incend. Bombs 


79 

18.4 

25.2 

0.05 


(1 MISCELLANEOUS BOMBS AND MINES 


TYPE 

TOTAL 

WEIGHT 

pounds 

TYPE of 
CHARGE 

WEIGHT of 

CHARGE 

pounds 

CHARGE- 
WEIGHT RATIO 
percent 

MAX. BODY 
DIAMETER 
inches 

LENGTH 
WITHOUT TAIL 
inches 

BODY WALL 
THICKNESS 
inches 

Mortar Grenade 

2.2 

TNT-cast 

4.2oz. 

12 

2.0 

4.2 

0.16 

Hand Grenade 
Chemical Warfare 





1.5 

4.1 

0.026 

Plane Destroying 
Bomb 

6.6 

TNT 



Dimensions in inches- 
7.5 x 6.5 x 2.8 


Ring Charges 
(2 sizes) 

A- 2.64 
B- 7.04 

TNT - 
compressed 



inside 4.0 
inside 6.8 



Shrapnel 

9.0 

Tolite (TNT) 

1.0 

II 

3.9 

height 5.7 

0.08 

Tel le rmine 

19 

Tolite (TNT) 

II 

56 

12.8 

height 4.0 

1/16 

Bell Demolition 
Charges (2 sizes) 

A - 27.5 

B -110.0 

TNT 

TNT 






500-kg. D 
Parachute-mine 

MOO 


675 

58 

26.0 



1000-kg. C 
Parachute-mine 

2200 


1536 

70 

26.0 



1000-kg. G 

Bomb- mine 

2200 


1615 

73 

25.5 

78.0 



ABBREVIATIONS 


Sb. - THERMITE INCENDIARY CONTAINING AN EXPLOSIVE CHARGE 
EL - THERMITE INCENDIARY WITH ELECTRON METAL CASE (?) 


COMPILED FROM DATA IN THE U.S. WAR DEPARTMENT TECHNICAL MANUAL, TM-E9-I983, AND FROM DATA SUPPLIED BY THE 
BRITISH MINISTRY OF HOME SECURITY 


August 1943 














































WEAPON DATA 

PHYSICAL CHARACTERISTICS OF JAPANESE 
HIGH EXPLOSIVE AND INCENDIARY BOMBS 


A. HIGH EXPLOSIVE AND FRAGMENTATION BOMBS 


DESIGNATION 

FUZE 

SETTING 

TOTAL 

WEIGHT 

W 

pounds 

MAX. 

BODY 

DIAM. 

inches 

LENGTH 

WITHOUT 

TAIL 

inches 

WALL 

THICK¬ 

NESS 

inches 

TYPE 

OF 

CHARGE 

WEIGHT 

OF 

CHARGE 
w, Lb. 

CHARGE 
WEIGHT 
RATIO 
w/W, % 

REMARKS 

l/3-kg AA, 
grounded, Army 

Inst. 

0.66 

1.6 

4.6 

0.03 

TNT 

0.24 

32 

80° cone-end charge; air burst 
containers of 30 or 76 bombs. 

Bolo Bomb, AA 

Army 

Inst. 

0.87 

2.5 

4.4 

3^32 

CycIonite 
and TNT 

0.53 

60 

Parachute attached; air-to-air 
bombing. 

l/2-kg AA, 
grounded, Army 

Inst. 

0.90 

2.1 

2.7 

3/64 

RDX/TNT 

0.44 

49 


l-kg AA, 

Sphe rica1 Missile 


2.3 

5.5 

5.5 

0.1 

Black Pwdr 

bu rste r 



Paper wall. 32 pellets @ 2/3 
oz . 

l-kg AA 

Navy 

1 nst. 

2.2 

1.8 

8.4 

0.07 

TNA/HND 

0.69 

31 

cone-end charge; air burst 
container of 40 bombs. 

l-kg Anti-pers. 

Navy 

Inst. 

2.2 

2.4 

5.5 

1/32 

TNA/HND 

1 .1 

50 

36 i n air-burst container. 

10-kg Anti-pers. 
Type 94, Army 
substitute 

Inst. 

22 

4.1 

18.2 

1.0 

Black Pwdr 

1.2 

5.5 

Concrete case; steel central 
tube. 

15-kg Anti-pers. 

Army 

Inst. 

32 

4.0 

14.5 

1/32 

Picric 

burster 



Cast steel case filled with 
concrete and steel pellets. 

15-kg Anti-pers. 
Type 92 Army 

Inst. 

33 

3.9 

14.6 

0.53 

Picric 

9.7 

29 

I 

Body wall made of 26 steel 
r i ngs. 

30-kg Anti-pers. 
Type 1 , A rmy 
substitute 

Inst. 

63 

5.1 

19.9 

1/16 

Black Pwdr 

bu rste r 



Cast steel case filled with 
concrete and steel pellets. 

30-kg Anti-pers. 
Type 2, Army 
s ubstitute 

Inst. 

66 

5.1 

20.6 

1/16 

B1ack Pwdr 
burster 



Cast steel case filled with- 
conc rete 

30-kg GP, 

Type 99, Army 

Inst; short 
delay; 1 5-16 
seconds 

66 

5.9 

19.7 

0.29 

Picric 

26 

39 


32-kg Stream- 
1 i ned, Navy 

Inst. 

70 

7.6 

19.7 

1/4 




Resembles British Bombs. 

50-kg GP, 

Type 94, A rmy 

Inst; short 
delay;15-16 
seconds 

110 

7.1 

24.4 

0.27 

Picric or 
RDX/TNA 

44 

40 


50-kg Time Bomb, 
Type 1 4 94 
(mod) A rmy 

15-16 sec; 
2-24 hrs. 

1 10 

7.1 

23.2 

9/32 

Picric 

44 

40 

Type I can use ant i-wi thd rawa 1 
tail fuze. 

60-kg Type 3 

Navy 

Inst; short 
delay 

143 

7.9 

21.8 

0.28 

Picric 

86 

60 


60-kg Type 97 

Navy 

In Navy 

Ga i ne* 

124 

7.9 

21 .8 

0.28 

Hexan i te 
and TNA 

50 

41 


60-kg Anti-Sub 
Type 99 Navy 

3s, 10 sec. 
delays 

141 

9.4 

21.0 

0.18 

TNA/HND 

86 

61 


63-kg Stream- 
1ined , Navy 

Inst. 

139 

9.0 

25.5 



65.8 

47 

Resembles British Bombs. 

63-kg GP, 

Type 99 Navy 

Inst. 

139 

8.9 

25.5 

0.25 

Picric or 
TNA/HND 

70 

50 


100 -kg GP, 

Type 3 and 94 

Army 

Inst; short 
delay;15-16 
seconds 

220 

9.5 

31.2 

0.4 

Picric 

99 

45 


100-kg Time, 

Type 1 and 94 
(mod ) A rmy 

15-16 sec; 
2-24 hrs. 

238 

9.5 

30.2 

0.4 

Picric 

104 

44 

Type 1 can use anti-withdrawa1 
tail fuze. 

250-kg GP, 

Type 1, Navy 

Inst; short 
delay; 5 -125 
hrs. 

550 

13.8 

35.5 

0.25 

TNA/HND 

330 

60 


250-kg GP, 

Type 1, Blunt 
Nose Navy 

Inst; short 
delay 

378 

1 1 .7 

30.4 

0.5 

TNA/HND 

175 

33 

May use electric firing mech¬ 
anism for proximity bursts. 
Explosive-filled tail. 

250-kg Anti- 
Ship, Type 3 

A rmy 

245 secs. 

550 

1 1.8 

46.5 

0.5 

Picric 

4 TNT 

230 

42 


250-kg Explo- 
sive-fi 11 ed Ta i 1 
Type 3, Navy 

In Navy 

Ga i ne* 

650 

12.0 

39.6 

0.5 

TNA/HND 

263 

40 

Designed for better 
fragmentation of tail 


t - 



M 


▲ /> * 

1 


A(> 

M 


JAPANESE 

HE AND 

IB BOMBS 



J 


July 19»V5 


372 




rii ! 



























































JAPANESE HIGH EXPLOSIVE a INCENDIARY BOMBS 

continued 


I DESIGNATION 

FUZE 

SETTING 

TOTAL 

WEIGHT 

W 

pounds 

MAX. 

BODY 

DIAM. 

inches 

LENGTH 

WITHOUT 

TAIL 

inches 

WALL 

THICK¬ 

NESS 

inches 

TYPE 

OF 

CHARGE 

WEIGHT 

OF 

CHARGE 
w, lb. 

CHARGE 
WEIGHT 
RATIO 
w/W, % 

REMARKS 

II 250-kg GP, 

Type 92 Army 

In Navy 

Gaine* 

550 

1 1 .7 

59.5 

1/4 

Picric 

230 

42 

Length includes tail cone. 

250-kg GP, 

Type 98 Navy 

Inst; short 
delay; 

5-125 hrs. 

532 

12.0 

39.6 

0.5 

Picric or 
TNA/HND 

210 

40 


250-kg Time, 

Type 1 A rmy 

2-24 hrs. 

527 

11 .7 

45.4 

1/4 

Picric 

228 

43 

Anti-withdrawa1 device in 

nose 

250-kg Anti¬ 
sub,Type 1 Navy 

Inst; short 
delay;5.5 4 

10 secs . 

650 

14.0 

35.6 

0.25 

TNA/HND 

396 

61 

Mod 1 has anti-ricochet 
nose ring. 

250-kg SAP, 

Type 99 Navy 

In Navy 

Gaine* 

540 

1 1 .5 

39.7 

0.75 

TNA 

133 

25 


250-kg Stream¬ 
line Navy 

Inst; short 
delay 

556 

14.0 

44.5 

0.60 

Picric 

229 

41 

One-piece cast or forged 
steel body. 

500-kg AP, 

Type 2 Navy 

In Navy 

Ga i ne* 

1 100 

15.5 

38.5 

Nose-.7i 
Base: 1 

TNA/HND 

148 

13 


500-kg GP, 

Type 92 Army 

Inst; short 
delay 

1100 

14.5 

77.0 


Picric 

493 

46 

Length includes tail cone. 

500-kg Anti- 

Ship, Type 4 

Army 

245 secs. 

1123 

15.0 

57.5 

0.56 

Picric 

4 TNT 

540 

48 

Explosive-filled tail. 

500-kg SAP, 

Navy 

In Navy 

Ga ine* 

1080 

16.5 

45.0 

Nose:4 
Base :5 

TNA/HND 

457 

42 


800-kg GP. 

Navy 

Inst; short 
delay 

1820 

17.5 

62.0 


TNA 

770 

42 

One-piece forged steel 
body possibly carried 
in torpedo racks 

800-kg Type 3, 
#80 Land Bomb 

Navy 

Inst; short 
delay 

1584 

17.8 

71.1 

15/32 

TNA/HND 

922 

58 

Also delays incorporated in 
Navy G a i ne* 

800-kg GP, 

Type 3 Navy 

Inst; short 
del ay 

1760 

18.0 

72.0 


Picric 

842 

48 

May use electric firing 
mechanism for proximity 
bursts 

800-kg, AP, 

Type 99 Navy 

Short delay 

1642 

16. 1 

48.3 

Nose:4 
Base:2 

TNA 

66 

4 

One-piece forged machine 
steel...two base fuzes 


B. INCENDIARY BOMBS 


1 1—kg A rmy 

Inst. 

2.7 

2.1 

8.3 

3/8 

Thermite-filled magnesiurn containers dropped in clusters. 

5-kg 

1 nst. 

1 1 

3.7 

6.7 

1/8 

Thermite filled 

12-kg, Type 97 

A rmy 

Short delay 

26 

4.0 

14.5 

3/16 

Thermite-filled magnesium firepots; black powder ignition 
charges. 

32-kg,Shrapnel 
Type 99, Navy 

0-20; 5-20 
0-50 sec. 
air burst 
delay 

70 

5.7 

13.5 

0.19 

198 phosphorus-filled steel pellets; picric acid charge. 

50-kg, Type 97 

A rmy 

Inst; short 
delay 

1 10 

7.5 

26.4 

0.2 

Gas bomb used as incendiary. CS 2 solution of white phos¬ 
phorus with 475 rubber bungs...picric acid charge. 

50-kg, Type 100 

Army 

Inst; short 
delay 

96 

7.0 

23.8 

0.125 


60-kg, Type 3 

Navy 

0-20; 5-20; 
0-50 sec. 
air burst 
delay 

118 

7.8 

23.0 

0.12 

Three cylindrical cannisters each containing 87 white 
phosphorous-fit1ed steel pellets. Explosive tube of 
TNA/HND 

70-kg, Type 98 
Short Delay, 

Navy 

short delay 

156 

7.9 

21.8 

0.3 

"Electron" firepots filled with thermite scattered by 
black powder charge. 

70-kg, Type 98, 

Oil Navy 

short delay 

145 

9.5 

21.0 

0.18 

20-lb inflammable mixture; 75 -d b thermite scattered by 
black powder charge. 

1 70-kg, Type 1 

Navy 

In Navy 

Ga i ne* 

160 

9.5 

21 .0 

0.125 

Contains 182 cylindrical incendiary pellets and grey 
powder bursting charge. 

250-kg, Type 2 

Navy 

0-20; 5-20; 
0-50 sec. 
air burst 
delay 

550 

12.0 

40 

0.22 

750 steel tubes filled with incendiary metallic rubber 
mixture. 33 kg. bursting charge of H.E. or black pow¬ 
der scatters mixture over 175 yds. radius when air burst 
occurs 100 ft. above ground. 


*Four types of Navy Gaine are known. Type A has delays of 0.014, 0.017, 0.025 and 0.031 seconds; Type B is instanta¬ 
neous; Type C is instantaneous; Type D has selective delay from a fraction of a second to 1.5 second. 


Source: US Navy Bomb Disposal School and Ordnance Department, US Army. 
































































WEAPON DATA 

PHYSICAL CHARACTERISTICS OF 
AMERICAN LAND MINES AND FIRING DEVICES 


1 


A7a 

AMERICAN 
LAND MINES 


A: LAND MINES 


DESIGNATION 

THICKNESS 
OR HEIGHT 

inches 

DIAM OR 
WIDTH 

inches 

TOTAL 

WEIGHT 

founds 

CASE 

EXPLOSIVE 

FUZE 

FORCE TO 
OPERATE 

pounds 

FUZE FUNCTION 

REMARKS 

TYPE 

WEIGHT 

pounds 

I Mine, 

Anti-Tank, 

Ml 

4 

8 diam 

10.6 

Steel 

Cast 

TNT 

5.5 

Ml 

500 center 
250 edge 

Pressure cuts shear 
pin. Balls release 
striker 

No longer in produc¬ 
tion. Booster inte¬ 
gral with fuze. Spi¬ 
der 8.2 in diameter. 

Mine, 

Ant i-Tank, 

Ml A1 

4 

8 d iam 

10.6 

Steel 

Cast 

TNT 

5.5 

Ml A1 

500 center 
250 edge 

Pressure cuts shear 
pin. Balls release 
str iker 

Booster separate from 
fuze. Spider 8.2in 

Ml A2 

500 center 
250 edge 

Same as mine with fuze 

Ml A 1 except fuze MIA2 
has more powerful de¬ 
tonator to insure high 
order detonat ion.Sp i- 
der 8.2 m diameter. 

I Mine, 
Anti-Tank, 

M4 

4 

8 diam 

10.6 

Steel 

Cast 

TNT 

5.5 

M4 

500 

"Cricket" metal dia- 
phragm snaps strik¬ 
er down 

2 activator wells* : 
side, bottom.Internal 
construction of fuze 

M4 makes mine safe to 
re-use. Spider 8.2xn 
diameter. 

Mine, 

Anti-Tank, 

M5 

5.5 

10 diam 

14.5 

Ceramic 

TNT or 
Tetr y- 
tol 

5.6 

M5 

Chem. 

275-425 

Pressure breaks glass 
vial. Chem. ignites 
flash mixture 

1 activator well* : 
bottom..fuze made of 
plastic. 

Mine, Heavy 
Anti-Tank, 

M6 

3.25 

12.5 

diam. 

20 

Steel 

Cast 

TNT 

12 

M600 

Chem. 

300-400 

Piston crushes glass 
vial. Chem. ignites 
flash mixture 

2 activator wells*: 
side; bottom. Sol id 
pressure plate 

Mine, Light 
Anti-Tank, 

M7 (or Anti- 
Personnel-see 
remarks) 

2.5 

4.5x7 

4.5 

Steel 

Tetry- 

tol 

3.25 

M60I 

Chem. 

300-400 

Piston crushes glass 
vial. Chem. ignites 
flash mixture 

1 activator well*: 
side. Any standard 
firing dev ice may be 
used in activator well 
to convert to anti¬ 
personnel mine. 

Mine, Anti¬ 
personnel , 

M2 

(M2A1,M2A2, 
M2A3.M2A3BI, 
M2A3B2.M2A4, 
M2A4B2) 

6.12 

Body: 
2.5 
diam. 
Base: 

54 diam. 
or 3x4 

Shell: 

2.5 

Total: 

5 to 
6.5 

Steel 

or 

Malle¬ 

able 

iron 

Flaked 

TNT 

0.34 

M2 

M2AI 

PULL 

PRESS 

Pressure or pull on 
trip wire releases 
spring driven strik¬ 
er 

3 prongs...pressure 
on 1 or more prongs 
or pull on release 
pin releases spring 
driven str iker. 

Various mods differ | 
in manufacturing de¬ 
tails of base. Pro¬ 
jects 2i lb shell 
which detonates 6-8 
ft from mine. Lethal 
range 30-60 ft. Dan¬ 
gerous to 150 ft .Any 
standard firing de¬ 
vice with igniter 
tube may be used as 
a fuze. 

3-6 

20-40 

6.5 

M6 

6-10 

10-30 

Mine, Anti- 
Personnel, 

3.5 

3.5x5.4 

9.6 

Cast 

Iron 

Flaked 

TNT 

0.85 

M3 

M3AI 

3-6 

20-40 

Lethal range approx. 

30 ft. 3 activator 
wells*: Top, side, 
and end. 

M7 

6-10 

10-30 


‘Activator wells have standard thread to fit any of the standard firing devices listed below. These may be used for anti¬ 
personnel ,dev ices or for otherwise booby trapping mines. 

Note: In addition to the mines listed above, various demolition charges, the bangalore torpedo, hand grenades, etc. may 
be equipped with one or more of the standard firing devices listed below and used as anti-tank or anti-personnel mines. 


Source: 


Publications of War Department; Ordnance Department, US Army; Office of the Chief of Engineers-, US Army; Bureau 
of Ordnance, US Navy; and US Navy Bomb Disposal School. 


Ref: PTM No. 110 
July 1945 



374 




















































]»: FIRING DEVICES 



DESIGNATION 

FORCE TO 

OPERATE, Lb 

r 

METHOD OF FUNCTIONING 

REMARKS 

Firing Device, 

Pull Type, Ml 

3-6 pull 

Pull on release pin releases spring driven 
striker 


Firing Device, 

Pul 1 Friction Type, M2 

3-9 pull 

Pulling coated wire through friction com¬ 
pound ignites compound. 

Made of plastic for use In non- 
metal lie mines or booby traps. 

Fir ing Device, 

Pressure Type, MIAI 

20 press 
(see remarks) 

Moving trigger pin inward allows spring 
driven striker pin to operate 

Operates on 5 lb press with trig 
ger spring removed. Has adjust¬ 
able extension rod with 3 prongs 

Firing Device, 

Release Type, Ml 

Restraining load 
at least 2 lb. 

Removal of restraining load allows spring 
driven hammer to drive striker pin. 

In sheet metal box, 

1-7/8 x 1-7/8 x 2-3/8 inches 

Fir ing Device, Pul 1 
Release Type, M3 

6-10 pull or ten¬ 
sion release 

Pull or release of tension on release pin 
releases spring driven striker 


Firing Device, Pres¬ 
sure Release Type,M5 

Restraining load 
at least 5 lbs. 

Removal of restraining loadallows spring 
driven striker to detonate cap. 

In sheet metal box 

1-3/4 X 15/16 X 11/16 inches 

Firing Device, 
Combination, Ml 

3-6 pull or 20 
press 

Pressure on cap or pull on release pin re¬ 
leases spring driven striker 

With igniter or blasting cap this 
is fuze M2 or M3 for anti-person¬ 
nel mines M2 and M3 

Fuze 

Combination, M6 

6-10 pull or 

10-30 press 

Pressure on one or more prongs or pull on 
release pin releases spring driven striker 

Firing devices complete with ig¬ 
niter. M6 has black powder igni- 
ter; M7 has blasting cap.Used as 
fuzes in anti-pers. mines M2,M3 

Fuze 

Combination, M7 

6-10 pull or 

10-30 press 

Pressure on one or more prongs or pull on 
release pin releases spring driven striker 

Firing Device 

Delay Type, Ml 

15-25 to crush 
ampule 

Crushing ampule releases corrosive liquid 
which eats away restraining wire, releas¬ 
ing spring-driven striker pin. 

Widely variable delays, color cod¬ 
ed on safety tab. Delay is 

strongly temperature dependent. 

Detonator, 

15-second Delay, Ml 

5-20 pull 

Pulling coated wire through friction com¬ 
pound causes flash igniting 15 sec. delay 
powder train. 

Made of plastic. May be used un¬ 

der water. Complete with blast¬ 
ing cap as igniter. 

Firing Device (Navy) 
Demol it ion, Mk 1 mod 0 

31 pull, release, 
or pressure 

Pressure on cap or pull or release of trip 
line releases spring driven striker 

Mkl mod 0 and Mk 1 mod 1 differ in 
mounting details. Mkl mod 1 rat- 
chet takeup for adjusting trip 
line. Can be used for pull-re- 
lease or pressure, but not for 
both. 

Firing Device (Navy) 
Demolit ion, Mkl mod 1 

11-16 pull, re¬ 
lease or pressure 

Pressure on cap or pull or release of trip 
line releases spring driven striker 

Firing Device (Navy) 
Demolition, Mk6 mod 0 

concussion detonator 


Air or water pressure snaps diaphragm 
through dead center driving striker pin 

For sympathetic detonation in 
air or water up to 12 ft deep. 
Various arming cells to give 
arming delays of 9-90 minutes 
in sea water at 60° F. 


All firing devices listed here have standard threaded coupling and may be used to detonate anti-personnel mines, demoli¬ 
tion charges, bangalore torpedoes, hand grenades, etc. which have standard threaded activator wells. Igniter tube, non¬ 
electric blasting cap, or Activator Ml must be used with all firing devices uhless otherwise noted (Fuze M6, Fuze M7, 
Detonator Ml). Primacord, properly attached, may be used to connect firing device to demolition charge. 



375 































WEAPON DATA 

PHYSICAL CHARACTERISTICS OF AMERICAN 
DEMOLITION, SHAPED AND LINE CHARGES 

A: DEMOLITION CHARGES 


DESIGNATION 

LENGTH 

WIDTH 

THICKNESS 

TYPE 

WEIGHT 

TOTAL 

CASE 

REMARKS 


inches 

inches 

inches 


pounds 

WEIGHT 

MATERIAL 








Pounds 




DEMOLITION CHARGES, U f S. ARMY 


Demolition Block, Chain, Ml 

M8 

9 

4i 

Tetrytol 

20 

22 

Cloth 

Bag 

8 blocks, strung on pri- 
macord, in bag. 

Demolit ion Block, M2 

11 

2 

2 

Tetrytol 

2.4 

2.5 

Paper 

Issued as 8 blocks in 
bag with strap. 

Demolition Block, M3 

11 

2 

2 

Comp C-2 

2i 

2i 

Paper 

Issued as 8 blocks in bag 
with strap. 

Demolition Block, M4 

6 

1 

18 

Comp C-2 

1 

2 

5 

Paper 


Block, TNT, 5 -lb. 

3 

* le 

1 — 

1 3 2 

1 ff 

Pressed TNT 

1 

2 

1 

2 

Cardboard 


Block, TNT, l-lb 

7 

1 -H 

1 H 

Pressed TNT 

1 

1 

Cardboard 
Metal Ends 

Two i-lb Blocks in one 
container. 

Block, Nitrostarch, 5 -lb. 

2 s 

18 

li 

Nitrostarch 

1 

4 

1 

4 

Paper 

Three-lb Blocks wrap¬ 
ped together. 

Block, Nitrostarch, 5 -lb. 

3 rs 

1 n 

1 If 

Nitrostarch 

1 

2 

1 

2 

Cardboard 
Metal Ends 


Block, Nitrostarch, l-lb. 

2{ 

25 

2i 

Nitrostarch 

l 

l 

Paper 

Four A-1b Blocks wrap¬ 
ped together. 

Cratering Explosive 

17 

85 -in. diam. 

Ammonium 

Nitrate 

40 


Metal 


Commercial Dynamite, 5 -lb. 

8 

li-in. diam. 

Dynamite 
40%,50%,60% 

1 

2 

1 

2 

Paper 



1 


1 -' 


V7b 


AMERICAN 


DEMOLITION CHARGES 


DEMOLITION CHARGES, U.S. NAVY 


Demolition Charge, Mk2 Mod 0 

14.2 

9.25 

9.25 

TNT 

55i 


Steel 

For electrical firing 

Demolition Charge, Mk2 Mod 1 

14.2 

9.25 

9.25 

TNT 

55i 


Stee 1 

For electrical or me- 
chanica1 firing. 

Demolition Charge, Mk2 Mod 2 

14.2 

9.25 

9.25 

TNT 

55^ 


Steel 

Has standard threaded 

activator we 11 

Demolition Charge, Mk3 

3 — 

° 10 

1 — 

1 3 2 

1 — 

1 3 2 

Pressed TNT 

1 

2 

1 

2 

Cardboard 
Metal Ends 

Same as Army Block, 

TNT i-lb. 

Demolition Charge, Mk4 

3 — 

0 10 

1 — 

1 — 

Cast TNT 

1 

2 

1 

2 

Cardboard 

Two tetryl pellet boos¬ 
ters. 

Demolition Charge, Mk5 

13 

13 

13 

TNT 

120 


Fiber 

Board 

2A-lb Tetryl booster 
Obsolescent; See Mkl4 

Demolition Charge, Mk9, Mod 0,1 

13 

13 

13 

Cast TNT 

112 

115 

Steel 

Fitted with standard 
bomb nose fuze seat 
for l8-in. fuzes. 

Demolition Charge, MklO 

11 

2 

2 

tetrytol 

2 i 

2 i 

Paper 

Same as one section of 
Army Demolition Block, 
Chain Ml, with detonat¬ 
ing cord attached. Is¬ 

sued as 8 blocks in cloth 
bag with strap. Obsolete 

Demolition Charge, Mkl4,Mod 0 

13 

13 

65 

Cast TNT 

485 

50 

F i ber- 
board 

46- 1 bs Cast TNT p 1 us 2i- 1 b 
tetryl booster. Self-con¬ 
tained detonating cord . 

Demol i t i on Charge, Mkl4,Modl 

13 

13 

65 

Cast TNT 

49 

50 

Fiber- 

Board 

No booster. Designed for 
sympathetic detonation. 

Demolition Charge, Mk20 

12 

2 s 

18 

Comp C-2 

25 

2 s 

Paper 

Issued as 10 blocks in 
haversack with strap.Two 
sacks issued together as 
Dem. Outfits, Mkl27. 


IS- SHAPED CHARGES cone-end 


-=- 

DESIGNATION 

OVERALL 

LENGTH 

STAND- 

CONE 

CONE 

CONE 

LINER 

CHARGE 

TOTAL 

CASE 

REMARKS 


LENGTH 

OF BODY 

OFF 

DIAM. 

ANGLE 

THICKNESS 

MATER IAL 

TYPE 

WEIGHT 

WEIGHT 

MATERIAL 



inches 

inches 

inches 

inches 

degree. 

inches 



pounds 

pounds 




SHAPED CHARGES, U.S. ARMY all have standard threaded activator well. 


Charge, Shaped, 10-lbMI 

13.5 

8.8 

4.7 

6 

80 

0.125 

Stee 1 

TNT 

9.5 

13 

Stee 1 

Obso1ete. 

Charge, Shaped, 10-lb M2 

15.8 

10.2 

5.6 

6 

60 

0.39 

Glass 

Pen- 

10 

13.5 

Plast ic 

Standoff t ube 
7.5 in. diam. 

Charge, Shaped, 10-1 b M2A1 

14.3 

8.7 

5.6 

6 

60 

0.39 

Glass 

to- 
1 ite 
50/50 

10 

13.4 

Impreg. 
Cloth 

Same as M2 with 
top reduced in 

1 enqth. 

Charge .Shaped, 15-lb, M2A3! 

16.4 

10.9 

5.4 

6 

60 

0.39 

Glass 


11 .5 

14.7 

Fiber-Bd. 


Charge, Shaped, 40-1b M3 

29.5 

15.4 

14.1 

9.5 

60 

0.16 

Steel 


29.2 

43.5 

Stee 1 

Detachab1e 1 egs 


CAVITY CHARGE CONTAINERS, U.S. NAVY 


Cavity Charge Container,Mk 1 

78 

4 a 

3 

28 

42 

0.06 

Steel 

Comp 

C-2 

2/3 


Steel 

Empty contain- 
e rs to be fi 1 - [ 

Cavity Charge Container ,Mk2 


li 

8 

1 

80 

0.03 

Steel 

8 oz 


Steel 

Cavity Charge Container,Mk3 

10 

4 

6 

3 

80 

0.09 

Steel 


1 f 


Steel 

led Comp C-2 


Ref: PTM No. IIO 
July 1945 





















































































































































C: LINE CHARGES 




Publications of War Department; Ordnance Department, US Army; Office of the Chief of Engineers, US Army; Bureau 
of Ordnance, US Navy; and US Navy 8omb Disposal School. 


Source: 







































































































WEAPON DATA 


LOW LEVEL BOMBING 



SPEED OF PLANE SPEED OF PLANE 


miles per hour knots 



ALTITUDE, hundreds of feet 


This sheet gives flight characteristics of botabs released from low altitude (up to 
3,000 ft), based on the trajectory in a vacuum. True striking velocity and angle of 
impact will both be less than values read from chart, but at the highest plane speed 
and altitude on graph, the error in striking speed is 18% for the 100 lb G.P. bomb 
and 1% for the 1000 and 2000 G.P. Errors in impact angle are 3° or less. For data 
on level-flight boitbing from altitudes above 2000 ft it is advisable to use sheets 
following, which give actual flight characteristics for individual bombs. 

HORIZONTAL FLIGHT: Locate a point on the graph by projecting upward from the given 
altitude and across from the given plane speed. Using this juncture, interpolate be¬ 
tween the solid-line curves to obtain striking velocity and between the broken-line 
curves to read angle of impact (measured from the vertical). 

DIVE OR CLIMB: Magnitude of striking velocity is determined same as for horizontal 
flight. Impact angle is found by reading an angle from the chart as for horizontal 
flight and correcting it by means of the angle of dive or climb, using the nomogram. 

Ex amp les: Dotted lines on graph show that a bomb dropped from a plane flying at a 
speed of 210 mi/hr at an altitude of 1150 ft in either horizontal or inclined flight 
will strike the ground at a speed of 410 ft/sec. If this plane is flying level, the 
impact angle (measured from vertical) will be about 48°; if at an angle of 40° the 
impact angle (see dotted line on nomogram) will be about 35°. 


FORMULAS: BOMB TRAJECTORY IN VACUUM IS BASED ON FOLLOWING RELATIONS. 

X* 1.467 Vo t cos.a 


Vl.467v/vi + 29.9h 


sin Go= 


✓ V*+29.9h 


sinG a = sin Go cosa= 

vV;+ 29.9h 


t=0.0456 j\/v| sin 2 at 29.9h ± Vo sin a] (use ♦ sign for climb, -sign for dive) 

where: 


V. s airplane speed,mi./hr. h = altitude of bomb release, ft. 

Vs« striking speed, ft./sec t * time of flight, sec. 

6o * impact angle for level flight, degrees from vertical 
Qq - impact angle for inclined flight,degrees from verticol 
a -angle of dive or climb, degrees from horizontal 
X * horizontal range of bomb trajectory, feet 


ANGLE CORRECTION 
FOR INCLINED FLIGHT 

ANGLE OF TRUE 

IMPACT FROM ANGLE OF 

ABOVE CHART IMPACT 

degrees degrees 



PTM No 


86 


December 1944 
















































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
IOO-lb GP, AN-M30 AND 250-lb GP, AN-M57 


100-lb. <;i> AN-M 30 



1250-lb. (il> AN-M 57 



The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 


Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this Juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15%; in impact angle, 4°. 

Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 


15 5 


- * 


JL FLIGHT 
100-lbGP; 250-lbGP 


August 1944 


nautical milas/hour nautical milas/hour 



























































































































































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
500-lb GP, AN-M64 AND 500-lb SAP, AN-M58 


I r> 6 * 

JL FLIGHT 
500-lb GPi 500-lb SAP 



Xs V. 
n, 

<b o 
c*. ^ 

$ 

£ ^ 
5 ? 


5(M)-1]j SAP, AN-M 5o 



Xf v 

* 2 

<o ^ 

£ 5 

N 

$i 


The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 

Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this Juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15%; in impact angle, 4°. 

Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 

August 1944 


380 


\ v I . I 1 U Lj-d/i 1 1 a li 
































































































































































































































































































WEAPON DATA 


STRIKING VELOCITY AND ANGLE OF IMPACT: 
lOOO-lb GP, AN-M65 AND IOOO-lb SAP, AN-M59 


11 

M- FI 


>7 


FLIGHT 
IOOO-lbGPi IOOO-lbSAP 



- 300 


« 

400 

<b 

Vi 

350 S 


I 


- 250 


200 


- 150 


- 100 


- 50 


l- 0 


1000-lb SAP. AH-M59 



400 


<i> 

4> 

* 

<»> 

<S 

v 


% 

S 


■ 300 


- 250 


- 200 


- 150 


- 100 


■ 50 


The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 

Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15#; in impact angle, 4°. 

Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground. Maryland 

August 1944 


381 


nautical miles/hour nautical miles /hour 































































































































































































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT 
lOOO-lb AP, AN-Mk33 AND IOOO-lb AP, M 52 Al 


i> o * 
> O 

FLIGHT 
1000-lbAP: Mil 33.M52 


1 1 

M. FL 



V 

<b ^ 

5 < 

- 

% H) 

Sl 


1000-lbAP, MSB Al 



Ss v. 
o 

<»> O 
t*. < 

* ^ 
$ S) 

v C 


The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of Impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 

Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this Juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15/6; in impact angle, 4°. 
Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 

August 1944 


382 


































































































































































































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
1600-lb AP, AN-Mkl AND 2000-lb GP, AN-M66 



-■L FLIGHT 

1600-lb APi 2000-lbGP 

J 



2000-lb GP, AN-M66, AN-M34 



V 

* 

a 


o> 

V 

</> 

§ 


ALTITUDE , 
thousands of feet 

The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 


Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this Juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15/S; in impact angle, 4°. 


Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 


August 1944 


nautical miles /hour nautical miles /hour 














































































































































































































































WEAPON DATA 


STRIKING VELOCITY AND ANGLE OF IMPACT: 
2000-lb SAP, MI03 AND 4000-lb LC, AN-M56 


200 <>-]b SAP, M107. 



The solid line curves give striking velocity (feet per second) and the broken-line curves give angle of impact (degrees 
from the vertical) for bombs released from a plane in horizontal flight. 


Locate a point by projecting upward from a given altitude and across from the given plane speed. Using this juncture, 
interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15%; in impact angle, 4°. 

Prepared from data supplied by the Ballistic Research Laboradory, Aberdeen Proving Ground, Maryland. 


f 

/ 

| 

BIO *1 

J 

1 

- FLIGHT 

2000- 

lb SAP; 4000-lb LC 

J 


384 


Revised: 
July 1945 


nautical miles/hour nautical miles /hour 




































































































































































































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
12,000-lb GP, TIO AND 22,000-lb GP, TI4 


I r> V2 

FLIGHT 

12000-lb GP; 22000-lb GP 



T5 W 
* 3 

O 

o %» 

W 6 
a 

d 

v o 

2 S 

d 

c 



• w 
"d a 
*> o 
c 

</> 

*/> 

*> 

d 

t* 6 

<o d 
u 

f- 

3 *M 

w 3 
*•-> d 
c 


The solid line curves give striking velocity (feet per second) and the broken-line curves give angle of impact (degrees 
from the vertical) for bombs released from a plane in horizontal flight. 

Locate a point by projecting upward from a given altitude and across from the given plane speed. Using this juncture, 
interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15%; in impact angle, 4°. 

Prepared from data supplied by the Office of the Chief of Ordnance, U. S. Army. 


JUNE 1945 


385 



















































































































































WEAPON DATA 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
90-lb FRAG.M82 AND 260-lb FRAG., AN-M81 


I MS 

JL FLIGHT 
90-lb F-, 260-lb F 




The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 

Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this Juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15 %; in impact angle, 4°. 


Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 


August 1944 


true surface speed, true surface speed, 

noutica / miles /hour nautical miles /hour 



























































































































































































































WEAPON DATA: INCENDIARIES 

TRAJECTORIES AND BALLISTIC DATA 
FOR AMERICAN INCENDIARY BOMBS AND CLUSTERS 

A= COMPARISON OF TRUE TRAJECTORIES FOR 25,000ft. RELEASE ALTITUDE a 250mph A.S. 

ALTITUDE, feet 
25,000 


I b<m> 

JL | B FLIGHT 
GENERAL 


21,000 


NOTE: 

these are true trajectories allowing for 
continuous variations in density of the 

atmosphere.range for any release 

altitude otner than 25,000 feet cannot 
be read from these curves 



6-lb, AN-M69 bombs in 
Quick-opening Clusters 

1-lb, AN-M50 bombs in 
Quick-opening Clusters 

100-lb IB, AN-M17 

6-lb, AN-M69 bombs in 
Ml 8 (E6R2)A imable Clusters 

1-lb, AN-M50.bombs in 
MI7AI Aimable Clusters 

00-lb GP, AN-M30 

for comparison 

500-lb IB, AN-M76 

500-lb GP , AN-M61 

for comparison 


Aimable Clusters opened 
at 5000 feet 


Ovals represent plan views 
of ground patterns . 

10 II 12 13 II 

RANGE, thousands of feet 

SOURCE: Based on data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Aberoeen, Maryland 


April 1945 


387 





















































































































































































































]>: graph of range for any dropping altitude 



DROPPING ALTITUDE Jeet 


DROPPING ALTITUDE Jeet 
0 



5,000 <4* 


10,000 < 4 * 


15,000 •••••••••••••••< 


20,000 


25,000 


30,000 


!••••••«♦••••••••••• 


SOURCE: Based on data in Ordnance Bombing Tables, U. S. Army 



388 









































































































































































































































































































































































































<:: TABULATION OF COMPARATIVE BALLISTIC DATA 


(For true air speed of 250 mph. and zero range wind) 



BOMB DESIGNATION 

AN-M69 

AN-M50 

AN-M69 

AN-M47 

AN-M69 

AN-M50 

AN-M30 

AN-M76 

AN-M64 I 

CLUSTER DESIGNATION 

AN-MI3 

AN-M 7 

E46 


Ml8(E6R2) 

AN-MI7A1* 




CLUSTER TYPE 

QUICK- 

QUICK- 

AIMABLE 


AIMABLE 

AIMABLE 





OPENING 

OPENING 

opening at 


opening at 

opening at 







5000 ft. 


5000 ft. 

5000 ft. 




BOMBING TABLE: BT 

6-A-2 

4-B-l 

500-0-1 

I00-G-2 

500-K-2 

500-J-2 

I00-C-3 

500—F — 1 

500-A-3 

RANGE, feet 

2190 

3920 

- 

5830 

- 

- 

6070 

6230 

6330 

j TR AIL, mils 

1933 

888 

- 

220 

- 

- 

137 

77 

54 

TRAIL BEHIND AN-M64, feet 

4140 

2410 

- 

500 

- 


260 

100 

0 

> RELEASE LAG AFTER AN-M64,sec 

1 1 .3 

6.6 

- 

1 .4 

- 

• 

0.7 

0.3 

0 

> DROPPING ANGLE, degrees 

23.7 

38.1 

- 

49.4 

- 

- 

50.5 

51.3 

51.7 

1 TIME OF FLIGHT, sec 

32.7 

22.8 

- 

18.91 

- 

- 

18.42 

18.04 

18.00 

STRIKING VELOCITY, ft/sec 

230 

375 

- 

530 

- 

- 

575 

620 

625 


RANGE, feet 

2440 

4960 

6720 

7810 


8100 

8360 

8680 

8820 

TRAIL, mils 

1752 

819 

859 

233 

- 

259 

138 

78 

61 

TRAIL BEHIND AN-M64, feet 

6380 

3860 

2100 

1010 

- 

720 

460 

140 

0 

RELEASE LAG AFTER AN-M64,sec 

17.4 

10.5 

5.7 

2.8 


2.0 

1.3 

0.4 

0 

DROPPING ANGLE, degrees 

13.7 

26.4 

33.9 

38.0 

- 

39.0 

39.9 

41.0 

41.4 

TIME OF FLIGHT, sec 

54.4 

35.8 

41.7 

27.64 

- 

29.1 

26.57 

25.79 

25.71 

STRIKING VELOCITY, ft/sec 

230 

410 

230 

640 

- 

365 

715 

790 

795 


RANGE, feet 

2750 

5750 

8530 

9240 


9890 

0,090 

10,530 

10,700 

TRA 1L, mils 

1638 

766 

642 

233 


215 

136 

78 

63 

TRAIL BEHIND AN-M64, feet 

7950 

4950 

2170 

1460 

_ 

810 

610 

170 

0 

RELEASE LAG AFTER AN-M64,sec 

21.6 

13.5 

5.9 

4.0 

• 

2 .2 

1.7 

0.5 

0 

Dropping angle, degrees 

10.4 

21.0 

29.7 

31.6 

- 

33.4 

33.9 

35.1 

35.5 

TIME OF FLIGHT, sec 

73.4 

47.1 

49.5 

34.74 

- 

35.7 

33.07 

31.90 

31.77 

STRIKING VELOCITY, ft/sec 

230 

415 

230 

705 

- 

410 

•810 

900 

910 

• 

RANGE, feet 

3020 

6460 

9930 

10,440 

10,680 

1 1,320 

1 ,510 

12,090 

12.280 

TRA 1L , mils 

1546 

722 

530 

230 

379 

195 

135 

78 

65 

TRAIL BEHIND AN-M64, feet 

9260 

5820 

2350 

1840 

1600 

960 

770 

190 

0 

RELEASE LAG AFTER AN-M64,sec 

25.2 

15.9 

6.4 

5.0 

4.4 

2.6 

2.1 

0.5 

0 

DROPPING ANGLE, degrees 

8.6 

17.9 

26.4 

27.6 

28.1 

29.5 

29.9 

31.2 

3 1.6 

TIME OF FLIGHT, sec 

90.3 

57.3 

56.0 

41 .01 

49.8 

41.5 

38.75 

37.22 

37.04 

STRIKING VELOCITY, ft/sec 

230 

420 

230 

745 

230 

440 

860 

965 

980 


RANGE, feet 

3 370 

7200 

11,130 

11,500 

11,870 

12,570 12,770 

13,430 

13,650 

TRA 1 L , mils 

1467 

687 

463 

226 

329 

187 

134 

80 

68 

TRAIL BEHIND AN-M64, feet I 

0,280 

6450 

2520 

2150 

1780 

1080 

880 

220 

0 

RELEASE LAG AFTER AN-M64sec 

28.0 

17.6 

6.9 

5.9 

4.8 

3.0 

2.4 

0.6 

0 

DROPPING ANGLE, degrees 

7.7 

16.1 

24.0 

24.7 

25.4 

26.7 

27.1 

28.2 

28.7 

TIME OF FLIGHT, sec 

105.6 

66.5 

61.9 

46.77 

54.8 

47.1 

43.97 

42.09 

41.86 

STRIKING VELOCITY, ft/sec 

230 

425 

230 

765 

230 

465 

890 

1010 

1025 


RANGE, feet 

3740 

7930 

12,240 

12,470 

12,980 

13,670 

3,920 

14,670 

14,900 

TRA1L, mils 

- 

652 

416 

222 

297 

178 

134 

82 

71 

TRAIL BEHIND AN-M64, feet 1 

1,160 

6970 

2660 

2430 

1920 

1230 

980 

230 

0 

RELEASE LAG AFTER AN-M64sec 

30.4 

19.0 

7.3 

6.6 

5,2 

3.4 

2.7 

0.6 

0 

DROPPING ANGLE, degrees 

7.1 

14.8 

22.2 

22.6 

23.4 

24.5 

24.9 

26.1 

26.4 

TIME OF FLIGHT, sec 

- 

74.9 

67.4 

52.17 

59.7 

51 .8 

48.92 

46.71 

46.44 

STRIKING VELOCITY, ft/sec 

230 

430 

230 

780 

230 

480 

910 

1030 

1045 


o 

»••••• Q 

o 


o 

o 

o 

o 

CM 


o 

o 

o 

lO 

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8 

*• 

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co 


‘Opening altitudes of 8,000 to 13,000 feet, instead of 5,000 feet, have recently been recommended for AN-MI7AI 
c1uster 

Note for all aimable clusters: (a) Trails given above are true trails. Trails given in bombing tables are fictitious 
trails for setting into bomb-sight with times of flight and disc speeds given in bombing tables in order to get 
proper range to target, (b) Trails (true) given above were calculated by the following formula: 

traii = Aiminq point offset upwind for each 10° of drift (trail settinq zero) 

- sin I0 5 x (altitude [ 1000) 

Times of flight were then calculated from trail and dropping angle by standard formula. 



389 

































































































WEAPON DATA: INCENDIARIES 

STRIKING VELOCITY AND ANGLE OF IMPACT: 
IOO-lb IB, AN-M47 AND 500-lb IB, AN-M76 


I r> i 2 i} 

M. FLIGHT 

100-1b IB: 500-lblB 
v- -J 


100-lb IB. AN-M47 



500-lb. IB. AN-M7G 



The solid line curves give striking velocity (feet per second) and the broken-line curves give angle 
of impact (degrees from the vertical) for bombs released from a plane in horizontal flight. 


Locate a point by projecting upward from a given altitude and across from the given plane speed. 
Using this juncture, interpolate between curves to obtain striking velocity or impact angle. 

Accuracy: Errors in striking velocity read from the graph will not exceed 15#; in impact angle, 4°. 


Prepared from data supplied by the Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland 


December 1944 


nautical miles /hour nautical miles /hour 


























































































































































































































WEAPON DATA: INCENDIARIES 


LOADING DATA 

FOR INCENDIARY BOMBS AND CLUSTERS 

FOR MAXIMUM LOADING IN ALL CASES ON US. ARMY AIRCRAFT WITHOUT BOMB-BAY GAS TANKS OR OTHER SPECIAL EQUIPMENT IN BOMB-BAYS 



C 1 

AIRCRAFT 

LOADING 


PLANE 

BOMB DESIGNATION .» 

AN-M47 

AN-M50 

AN-M50 

AN-M52 

AN-M69 

AN-M69 

M74 

AN-M76 



CLUSTER DESIGNATION 

None 

AN-M7 

M17A1 

AN-M11 

AN-M13 

E46 

E48 

None 



ACTUAL WEIGHT, pounds-* 

72 

525 

465 

425 

425 

425 

525 

475 


15-7/2 

No. of clusters 

, 

40 

40 

40 

40 

40 

40 

_ 


No. of bombs 

— 

5120 

4400 

7680 

2400 

1520 

1520 

40 



Total weight. Tons 

- 

10.5 

9.30 

8.50 

8.50 

8.5 

10.15 

9.50 



Total heat, million BTU 

— 

66.2 

57.0 

86.0 

105.6 

66.9 

57.6 

88.4 


15-‘29 

No. of clusters 


40 

40 

40 

32 

40 

40 



No. of bombs 

144 * 

5120 

4400 

7680 

1920 

1520 

1520 

40 



Total weight. Tons 

5.18 

10.5 

9.30 

8.50 

6.82 

8.5 

10.15 

9.50 



Total heat, million BTU 

96.4 

66.2 

57.0 

86.0 

84.5 

66.9 

57.6 

88.4 


15-‘24 

No. of clusters 


12 

12 

12 

12 

12 

12 

_ 


No. of bombs 

52 

1536 

1320 

2304 

720 

456 

456 

12 


Series 

Total weight. Tons 

1.87 

3.15 

2.79 

2.55 

2.55 

2.55 

3.15 

2.85 



Total heat, million BTU 

34.8 

19.8 

17.1 

25.8 

31.7 

20.0 

17.3 

26.5 


11-17 

No. of clusters 


12 

12 

12 

12 

12 

++ 

12 

_ 


No. of bombs 

42 

1536 

1320 

2304 

720 

456 

456 

12 


F.G. 

Total weight. Tons 

1.51 

3.15 

2.79 

2.55 

2.55 

2.55 

3.15 

2.85 



Total heat, million BTU 

28.1 

19.8 

17.1 

25.8 

31.7 

20.0 

17.3 

26.5 


15-‘2(5 

No. of clusters 

•I* 

6 

6 

6 

6 

6 

6 



No. of bombs 

28 

768 

660 

1152 

360 

228 

228 

6 


Series 

Total weight. Tons 

1.01 

1.58 

1.39 

1.28 

1.27 

1.28 

1.57 

1.42 



Total heat, million BTU 

18.7 

9.9 

8.5 

12.9 

15.8 

10.0 

8.6 

13.3 


B-<25 

No. of clusters 

No. of bombs 

24 * 

6 

768 

6 

660 

6 

1152 

6 

360 

6 

228 

6 

228 

6 


Series 

Total weight. Tons 

0.87 

1.58 

1.39 

1.28 

1.27 

1.28 

1.57 

1.42 



Total heat, million BTU 

16.0 

9.9 

8.5 

12.9 

15.8 

10.0 

8.6 

13.3 


A-‘2(i* 

No. of clusters 

, 

6 

6 

6 

4 

6 

6 



No. of bombs 

16 

768 

660 

1152 

240 

228 

228 

6 


B 

Total weight. Tons 

0.58 

1.58 

1.39 

1.28 

0.85 

0.85 

1.57 

1.42 



Total heat, million BTU 

10.7 

9.9 

8.5 

12.9 

10.6 

10.0 

8.6 

13.3 


A-‘20* 

No. of clusters 


4 

4 

4 

4 

4 

4 



No. of bombs 

4 

512 

440 

768 

240 

152 

152 

4 


C.G.H. 

Total weight. Tons 

0.14 

1.05 

0.93 

0.85 

0.85 

0.85 

1.05 

0.95 


J.K. 

Total heat, million BTU 

2.7 

6.6 

5.7 

8.6 

10.6 

6.7 

5.8 

8.8 


A-3<» 

No. of clusters 


2 

2 

2 

2 

2 

2 



No. of bombs 

2 

256 

220 

384 

120 

76 

76 

2 


P-81 

Total weight. Tons 

0.07 

0.53 

0.47 

0.43 

0.43 

0.43 

0.53 

0.48 


Total heat, million BTU 

1.3 

3.3 

2.8 

4.3 

5.3 

3.3 

2.9 

4.4 


11 'I ** 

No. of clusters 

__ 

3 

3 

3 

3 

3 

3 



P -fi 

No. of bombs 

3 

384 

330 

576 

180 

114 

114 

3 



Total weight. Tons 

0.11 

0.79 

0.70 

0.64 

0.64 

0.64 

0.79 

0.71 



Total heat, million BTU 

2.0 

5.0 

4.3 

6.5 

7.9 

5.0 

4.3 

6.6 


P-40 

No. of clusters 


3 

3 

3 

3 

3 

3 



No. of bombs 

3 

384 

330 

576 

180 

114 

114 

3 



Total weight. Tons 

0.11 

0.79 

0.70 

0.64 

0.64 

0.64 

0.79 

0.71 



Total heat, million BTU 

2.0 

5.0 

4.3 

6.5 

7.9 

5.0 

4.3 

6.6 


rr o 

No. of clusters 


2 

2 

2 

2 

2 

2 



P-7>o 

No. of bombs 

2 

256 

220 

348 

120 

76 

76 

2 



Total weight. Tons 

0.07 

0.53 

0.47 

0.43 

0.43 

0.43 

0.53 

0.48 



Total heat, million BTU 

1.3 

3.3 

2.8 

4.3 

5.3 

3.3 

2.9 

4.4 



★ Internal loading only; for external loading add 4 - 100 lb. or 4 - 500 lb. clusters for 
A-20 G, H, J, K, and A-26B. 

★ * Omitting aft bomb-bay. 

★ Multiple suspension using toggle wires. 

++ Minor interference on two bottom inboard stations might reduce loading from 12 to 10. 


December 1944 



391 










































































































































































































































. 






ri ■ 


























WEAPON DATA 

PENETRATION OF REINFORCED CONCRETE 
BY AP PROJECTILES AND AP AND SAP BOMBS 


C)A1 

r.nwr.RF 


CONCRETE: 
PENETRATION 


BASED ON DATA DEVELOPED FOR THE CHIEF OF ENGINEERS 


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pQNFIDKNTIAIi; 


393 






































WEAPON DATA 

PENETRATION 

OF BOMBS AND PROJECTILES INTO SOIL 


C) A2* 

jam son 

, PENETRATION 



hundreds of feet/second 


L-path length 
penetration 


measured to the nose, for projectiles or bombs of various weights penetrating into several soils. 

Curves marked blunt, average, and sharp are for projectiles of different nose shapes as sketched. 

Where no appreciable effect of nose shape on penetration has been observed only a single curve is 
drawn. The dependence of penetration path length on projectile weight, as given by the nomogram^ 
agrees with observations for projectiles or bombs having caliber densities from 0.15 to 0.65 Ib/in. 

Most bombs and artillery projectiles have caliber density values (weight of projectile in pounds 
divided by the cube of the diameter in inches) within the above range. 

Trajectories in soils are usually straight for two-thirds or more of the path length, but curve 
near the end of the path (see sketch). For this reason final distance from the surface is usually 
10% to 30% less than the penetration path given here. 

Curves given are for average soil types. Penetrations into rich plastic clay are approximately 
30% greater than those observed in clay. The dotted curve at the bottom of the graph gives 
average penetration into good quality reinforced concrete, and is added here for rough comparison. 

EXAMPLE: The dotted line shows that a projectile of average nose shape and weight of 60 lb striking sandy loam soil with 
a velocity of 1700 ft/sec will have a path length of approximately 12.5 ft, measured to the nose. Because of the curvature 
of the underground trajectory, the actual penetration from the surface will be somewhat less. 

SOURCE: British and American tests with bombs and large caliber projectiIes at ve1ocities below 1100 ft/sec. Small caliber 
tests for the Corps of Eng i neers, U .S .A. extending over entire velocity range. The curves agree with measurements to ±20%. 



TYPICAL 

UNDERGROUND TRAJECTORY 


Revision of 2 A2 dated September 1944 


PTM No. 103 February 1945 
















































































WEAPON DATA 

PENETRATION OF GP BOMBS 

AND SMALL CALIBER BULLETS INTO SOIL 



A-BOMB PENETRATION for U.S. GP Bombs. 


DEPTH BELOW SURFACE, feet 

at end of penetration path 
40 


35 

30 

25 

20 

15 

10 


o 

l 

AM 
























































10 15 20 25 30 

ALTITUDE, thousands of feet 



at 

50 

2000-GP 

45 


40 

1000-GP 

35 

500-GP 

30 

250-GP 

25 

100-GP 

20 


15 


10 


DEPTH BELOW SURFACE, feet 
at end of penetration path 

30 


25 


20 


15 


10 


SA 

ND 

















- 






























DEPTH BELOW SURFACE, feet 
at end of penetration path 


i 

CLAY 








































































10 


2000-GP 


1000-GP 


500-GP 


250-GP 


100-GP 


2000-GP 

1000-GP 

500-GP 

250-GP 

100-GP 


20 25 30 

ALTITUDE , thousands of feet 

The curves give the depth below the surface for General Pur¬ 
pose bombs dropped from level flight at various altitudes.The 
depth is that measured from a level surface to the center of 
the bomb, delay fuzed to permit full penetration. 

The designations clay, loam, and sand are for average soil 
types. For soils of other types interpolation should be made 
from these curves.For example, the depth in a sandy soil may 
be expected to be between the values given for sand and the 
values given for loam. 

Bomb penetrations into soil vary due to the irregularities 
of curvature of the underground trajectory, and may vary ap¬ 
preciably due to inhomogeneities of the soil, water content 
of the soil, etc. The curves given here agree with the avail¬ 
able data to within + 20%. 


10 15 20 25 30 

ALTITUDE, thousands of feet 


]> - SMALL CALIBER BULLETS 

Penetration of small caliber jacketed bullets into soils is limited by the deformation of the soft tip at low velocities 
and stripping of the jacket from the core at high velocities.Such deformations result in increased resistance to motion. 

The table gives penetration and perforation data for small caliber service am¬ 
munition with soft jacket and hard core. The maximum thickness of a soil para¬ 
pet that can be perforated by a single hit at short range and the recommended 
minimum thickness of a soil parapet for protection against ten hits close to¬ 
gether are g iven .The protect ion is adequate only for positions more than twelve 
inches (25 to 30 calibers) below the top of the parapet. 




U.S. CALIBER 

.30 AP 


U.S. CALIBER .50 AP 

SOIL 

Maximum 

Average 

Parapet 

Parapet 

Max imum 

Average 

Parapet 

Parapet 


Expected 

Penetration, 

Th i ckness 

Thickness for 

Expected 

Penetrat i on, 

Th ickness 

Thickness for 


Penetration 

Short Ranae 

Perforated 

Protection 

Penetration 

Short Ranae 

Perforated 

Protect ion 

LOOSE SAND 

12 in 

lOi n 

13 in 

40 i n 

20 in 

16 in 

21 in 

64 in 

COMPACT SAND 

9^ i n 

7i in 

12 in 

30 in 

15 in 

12 in 

19 in 

46 in 

LOAM 

16 in 

12 in 

16 in 

44 in 

24 in 

20 in 

26 i n 

72 in 

PLASTIC CLAY 

23 in 

20 in 

23 in 

65 i n 

40 i n 

30 in 

36 in 

100 in 


SOURCE: The Bomb Penetration Curves are based on British and American tests with bombs and large caliber projectiles.The 
Small Caliber Bullet Tabulation is based on tests for the Corps, of Engineers, U.S.A. 



PTM Ho. 103 April 1945 


395 























































































NATIONAL DEFENSE RESEARCH COMMITTEE 
DIVISION 2, PRINCETON UNIVERSITY STATION 

ENGINEERING DATA 

PENETRATION PROFILES AND BALLISTIC LIMITS FOR REINFORCED 



() A7> 

CONCRETE: 
PROFILES 6 LIMITS 

CONCRETE SLABS 



396 





















































































STRIKING * n . 
OBLIQUITY * 0 


(3000) 


( 2000 ) 


(2500) 


(1500) 

PERFORATION 

LIMIT 


STICKING 
LIMIT 

SCABBING * 
LIMIT * 


(loop) 


(500) 


mH- 

STRIKING 

VELOCITY 

feet/second 

0 - 


MARCH,1944 


37mm M80 AP SHOT projectile useoin tests 


SCALC »N INCUES 


28 ° 


THUS SLABS) 


The charts show profiles of typical craters 
formed by the impact of 37mm M80 inert pro¬ 
jectiles without cap or windshield, fired 
against heavily reinforced concrete slabs 
cylinder tested at 5000-6000 psi compressive 
strength. Striking velocity is shown by the 
horizontal lines and striking obi iquity by 
the radial lines. The curves show the zone 
of ricochet and the limits of perforation, 
scabbing and sticking for thick and thin 
slabs. The reference point for any projectile 
is the point of impact of the projectile 
the slab face. 


on 


The charts may be used for general assess¬ 
ment of the effect of velocity and obliquity 
on damage to concrete. The various limits 
may be estimated, but since these limits are 
not always sharply defined some latitude 
must be allowed in making estimates. 


Mote: Data taken from experiments conducted 
for the Office of the Chief of Engineers. 


SCALE in inches 

for THICKondTHINSLABS 

12' &• O 17* 24* 



397 


















































































WEAPON DATA 

RICOCHET FROM WATER, SOIL AND CONCRETE 



RICOCHET 



ANGLE OF IMPACT WITH SURFACE 

901-1----i— 


angle of 
impact 


■ . ; 


.- 


... 




2500 

IMPACT VELOCITY,/t/i-ec 


The graph gives the limiting angle separating ricochet and penetration for water, soil or massive concrete as a function 
of striking velocity. For armor or mild steel plate the limiting angle is different for each plate thickness; these are 
not treated here. The curves apply to ordinary projectiles and bombs, without special attachments or nose shapes. 

The ricochet limits are represented in the form of bands, the width of each band including variation of many factors such 
as nose shape, moment of inertia, density of the projectile and density of the material. Each band on the graph sepa¬ 
rates two regions: ricochet occurs for combinations of striking velocity and impact angle below the band, no ricochet oc¬ 
curs for combinations above the band. The portions of each band with dotted edges are based on a small amount of data. 

In general, missiles having sharp noses, long slender bodies or low densities will have ricochet limits in the upper part 
of each band, while those having blunt noses, short bodies or high densities will have ricochet limits in the lower part 
of each band. Increasing the surface regularity or the density of the target generally shifts ricochet 1imits toward the 
lower part of each band. 

SOURCE: Soil and water ricochet data are from Aberdeen Proving Ground; concrete ricochet data are from the Office of the 
Chief of Engineers, U. S. Army. 


August 1945 


























































































































WEAPON DATA 

SCABBING OF REINFORCED CONCRETE 

BY AP PROJECTILES AND AP AND SAP BOMBS 


r 

111 s 

% 

f 1) 1 

m CONCRETE: 


SCABBING 


BASED ON DATA DEVELOPED FOR THE CHIEF OF ENGINEERS 


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June 1943 




























WEAPON DATA 

PERFORATION OF REINFORCED CONCRETE 
BY AP PROJECTILES AND AP AND SAP BOMBS 


t><; 1 

jjmd conci 


CONCRETE^ 
PERFORATION 


BASED ON DATA DEVELOPED FOR THE CHIEF OF ENGINEERS 

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June 1943 


400 





























WEAPON DATA 

PERFORATION OF REINFORCED CONCRETE 
BY SPECIFIC BOMBS AND ROCKETS 


(Ma 


OF R/C 


PERFORATION 

SPECIFIC 


BOMB 
(delay 
fuzed) 

ALTITUDE 

ft 

C 0NC 
PERF0RATI0 

RETE 

N, feet 

SOIL 

PENETRA' 

NON. ft 

CONCRETE PERFORATION, ft, WITH SOIL COVER OF 
VARIOUS THICKNESSES, ft 

3000 psi 

5000 psi 

Sand 

Loam 

2 ft 

4 ft 

6 ft 

8 ft 

1 C ft 

100-lb GP 
AN-M30 

5000 

1 .0 ft 

1 imited by 
case strength 

0.75 ft 

1 imited by 

case strength 

5 

8 

0.7 

0.5 

- 

- 

- 

10000 

7 

10 

0.7 

0.7 

- 

- 

- 

15000 

75 

1 1 

0.7 

0.7 

- 

- 

- 

20000 

8 

Hi 

0.7 

0.7 

0.5 

- 

- 

25000 

8 

Ml 

0.7 

0.7 

0.6 

- 

- 

250-lb GP 
AN-M57 

5000 

1.3 ft 

1 imited by 
case strength 

1.0 ft 

1 imited by 
case strength 

7 

10 

1 .0 

0.8 

- 

- 

- 

10000 

95 

135 

1 .0 

1 .0 

0.8 

- 

- 

15000 

ioi 

15 

1 .0 

1 .0 

1 .0 

- 

- 

20000 

11 

16 

1 .0 

1 .0 

1 .0 

0.8 

- 

25000 

1 1 2 

16 

1 .0 

1 .0 

1 .0 

0.8 

- 

500-lb GP 
AN-M43.M64 

5000 

1.7 ft 

1 imited by 
case strength 

1.3 ft 

1 imited by 
case strength 

8 

121 

1 .3 

1 .1 

0.9 

- 

- 

10000 

12 

17 

1 .3 

1 .3 

1 .3 

1 .1 

- 

15000 

135 

19 

1 .3 

1 .3 

1 .3 

1 .2 

- 

20000 


2 O 5 

1 .3 

1.3 

1 .3 

1 .2 

l.l 

25000 

15 

21 

1 .3 

1 .3 

1 .3 

1 .3 

1.2 

a_ ur> 

O <£> 

2 : 

-O ► 

— a- 

i =* 

o zz. 

O | 

O z 

— 

5000 

2.3 ft 

1 imited by 
case strength 

1 .7 ft 

1 imited by 
case strength 

io£ 

16 

1 .7 

1 .7 

1 .3 

1.1 

- 

10000 

15 

22 

1 .7 

1.7 

1 .7 

1 .7 

1 .3 

15000 

17 

24 

1.7 

1 .7 

1 .7 

1.7 

1 .3 

20000 

I 85 

26 

1 .7 

1.7 

1 .7 

1.7 

1 .7 

25000 

19 

27 

1 .7 

1 .7 

1 .7 

1 .7 

1.7 

2000-lb GP 
AN-M34,M 66 

5000 

2.9 ft 

1 imited by 
case strength 

2.1 ft 

1 imited by 
case strength 

13$ 

2 O 2 

2.1 

2.1 

2.1 

1.9 

1 .7 

10000 

195 

28 

2.1 

2.1 

2.1 

2.1 

2.1 

1 5000 

22 

3 15 

2.1 

2.1 

2.1 

2.1 

2.1 

20000 

24 

33i 

2.1 

2.1 

2.1 

2.1 

2.1 

25000 

24^ 

34^ 

2.1 

2.1 

2.1 

2.1 

2.1 

500-lb SAP 
AN-M58 

5000 

2.5 

2.0 

8 

1 25 

1 .7 

1 .4 

l.l 

- 

- 

10000 

3.0 

2.7 

12 

17 

2.4 

2.1 

1 .7 

1.3 

- 

15000 

3.5 

3.1 

135 

19 

2.7 

2.4 

2.1 

1 .8 

- 

20000 

3.8 

3.3 

I4i 

20j 

2.9 

2.6 

2.3 

1.9 

1 .6 

25000 

4.1 

3.5 

15 

21 

3.2 

2.8 

2.5 

2.2 

1.8 

a_ 

<t 

5000 

3.0 

2.7 

10 

16 

2.4 

2.1 

1 .8 

1 .5 

- 

C/5 

a> 

10000 

3.9 

3.5 

15 

22 

3.2 

2.9 

2.5 

2.2 

1.9 

— 2 

1 1 

O z 
o < 
o 

15000 

4.6 

4.1 

17 

24 

3.7 

3.4 

3.1 

2.7 

2.4 

20000 

5.1 

4.4 

182 

26 

4.0 

3.7 

3.3 

3.0 

2.6 

25000 

5.5 

4.7 

19 

27 

4.3 

4.0 

3.7 

3.3 

3.0 

a. 

C/5 

5000 

3.3 

3.0 

135 

-IM 

O 

CM 

2.7 

2.4 

2.1 

1 .8 

1.5 

10000 

5.1 

4.4 

195 

28 

4.1 

3.8 

3.5 

3.1 

2.8 

— O 

1 — 

15000 

6.1 

5.3 

22 

31 5 

4.9 

4.6 

4.3 

4.0 

3.6 

o 

O X 

o 

20000 

6.8 

5.8 

24 

335 

5.4 

5.1 

4.7 

4.4 

4.0 

cm 

25000 

7.2 

6.2 

24| 

345 

5.8 

5.5 

5.1 

4.7 

4.4 

a_ 

*** CO 
-O ** 

5000 

2.7 

2.5 

I0i 

16 

2.2 

1 .9 

1.7 

l.l 

- 

10000 

4.0 

3.5 

15 

22 

3.2 

2.9 

2.5 

2.2 

1 .9 

1 2- 
Q i 

15000 

5.2 

4.3 

17 

24 

3.9 

3.6 

3.2 

2.9 

2.5 

o <t 

20000 

5.9 

4.9 

I 85 

26 

4.5 

4.1 

3.7 

3.3 

2.9 

25000 

6.4 

5.2 

19 

27 

4.8 

4.4 

4.0 

3.7 

3.3 

1600-1 b AP 
AN-Mk 1 

5000 

3.4 

3.0 

1 2i 

19 

2.7 

2.4 

2.1 

1.9 

1 .6 

10000 

4.8 

4.2 

175 

26 

3.9 

3.6 

3.2 

2.9 

2.5 

15000 

6.2 

5.2 

20 

28 

4.9 

4.5 

4.1 

3.8 

3.3 

20000 

7.1 

5.8 

212 

30 

5.4 

5.0 

4.6 

4.3 

3.9 

25000 

7.8 

6.4 

22 

31 

6.0 

5.6 

5.2 

4-.7 

4.3 


MINIMUM 

ALTITUDE 

ATTACK 

OF 

VERTICAL 

CONCRETE 

WALLS 

THICK¬ 

NESS 

PERFO¬ 

RATED 

feet 


By 

Bombs 


1.3 


I .5 


2.0 


I .5 


2.0 


CONCRETE 
PERFORATION 
BY ROCKETS 


5-inch 
HVAR Mk 6 

2 .it feet 

11.75-inch 
AR Mk2 

4.5 feet 



The table gives the thickness of reinforced concrete and thickness of concrete with soil cover that can be perforated by 
GP, SAP, and AP bombs dropped from planes in level flight at 200 to 300 m.p.h. at various altitudes. The depth of pene- 
tratioh of the same bombs into soil is included for comparison. 

Bombs should be fuzed 0.025 seconds delay or longer to insure perforation before detonation. The values given in the table 
apply to bombs with this fuze delay. 

SOURCE: Based on Data Sheets 2A2*, 2CI, and Interim Memorandum No. M-13 of the Committee on Fortification Design. 


August 1945 


401 















































































































































WEAPON DATA 


PERFORATION OF PLASTIC PROTECTION 


DESCRIPTION 

PLASTIC PROTECTION CONSISTS OF A MIXTURE, IN PROPORTIONS BY WEIGHT AS GIVEN, OF THE FOLLOWING MATERIALS: COARSE MINERAL 
AGGREGATE (exner gravel) - 60%; LIMESTONE OUST FILLER - 30%; MASTIC BITUMIN and/or COAL TAR PITCH - 10%. A LAYER OF 
THIS MIXTURE IS BACKED BY A I/8-INCH TO I/4-INCH THICK PLATE OF MILD STEEL. TO INCREASE THE STRUCTURAL STRENGTH AS WELL 
AS THE STOPPING POWER OF THE MATERIAL, CHICKEN WIRE OR EXPANDED METAL IS EMBEDDED IN THE PLASTIC MIXTURE AT THE CENTER 
OR NEAR THE FRONT SURFACE. OCCASIONALLY, A FRONT PLATE OF 20-GAUGE (or heavier) STEEL IS APPLIED. 


/-\ 

(] <2 

PLASTIC 
PROTECTION 

[PER F ORATION 

V, ^ 



EFFECTIVENESS 

STOPPAGE OF THE PROJECTILE IS LARGELY DUE TO THE BREAKING-UP AND YAWING OF THE CORES BEFORE REACHING THE BACK PLATE. 
INASMUCH AS THIS PROCESS MAY OCCUR IN A LARGE NUMBER OF WAYS, THERE IS NO SHARPLY DEFINED LIMITING VELOCITY FOR A GIVEN 
THICKNESS OF THE MATERIAL SUCH THAT FOR HIGHER VELOCITIES ALL BULLETS WILL PERFORATE WHILE FOR LOWER VELOCITIES NONE WILL. 
IT MAY BE SAID ONLY THAT A CERTAIN PERCENTAGE OF PROJECTILES TRAVELING AT A GIVEN VELOCITY WILL BE STOPPED BY A GIVEN 
THICKNESS OF PLASTIC PROTECTION. 


AMOUNTS OF PLASTIC PROTECTION, MILD STEEL AND SPECIAL 
TREATED STEEL REQUIRED FOR " ADEQUATE PROTECTION " 


(5%PERFORATION AT NORMAL 
IMPACT AND CLOSE RANGE) 


PROJECTILE 

STRIKING 
VELOCITY 
ft. /sec. 

PLASTIC PROTECTION 

MILD STEEL 

SPECIALTREATEDSTEEL 

• l? 

inches 

t 

inches 

w 

lbs./sq.ft. 

t 

inches 

w 

lbs./ sq.ft. 

t 

inches 

w 

Ibs./sq.ft. 

British -.303inch,Mk VII, Bo II 

2440 

1 /8 

l-'/8 

20 



</4 

1 0 

American -30 caliber Ball 

2560 

3/16 

1- 1/16 

23 





British -.303inch A P 

2440 

3 /l6 

2-1/4 

34 

1.04 * 

* 

« 

CVJ 

.71 * 

29 * 

American-30 col., M-2 AP 

2580 

3/16 

3-1/8 

44 

1.10 

43.1 

3/4 

34 

British -.55 inch A P 

2400 

*/4 

5 

72 





American-.50 cal.,M-2 AP 

2900 

3/16 

5to6 

70 to 86 

2.20 * 

89.8 * 

1- '/2 

60 

British -20 mm. AP 

2750 

1/4 

7-7/e 

110 





Splinter from US. 250-lb. 
G.P. Bomb at 37.5 feet 


3/16 

1-1/2 

26 

1.35 

55 .0 

0.9 

36 


NOTES t B - thickness of mild steel booking plote * these figures are estimotes derived from the assumption that the thickness per- 

t - totot thickness (including backing plate) forated is directly proportional to the mass of the projectile and to the square of 

W-total weight per unit area (including backing plate) the striking velocity and inversely proportional to the square of the caliber. 


PROBABILITY of 
PERFORATION 
percent |00 


90 

80 

70 

60 

50 

40 

30 

20 

10 

0 




REPRESENTATIVE CURVES COMPARING HOMOGENEOUS' 
HARD ARMOR PLATE AND PLASTIC PROTECTION 










ll 



7T 


-w 


CU R VE 

A 


PLASTIC PROTECTION (EXNER SRAVEU 
mild steel backing plate -*/i6 inches thick 
total thickness 
weight 

type of projectile 
perforation limit 


- 1.81 inches 

- 30 Ibs./sq. ft. 

- .30cal.,M2 A.P. 

- Navy (complete) 


' curves illustrate relative 
sharpness of limit only... they 
- represent different weights 
of protection ond different 
definitions of perforation 
' Jim it... 


CUR VE 

B 


HOMOGENEOUS HARD ARMOR PLATE 


Brinell hardness number 
thickness of plate 
weight 

type of projectile 
perforation limit 


- 415 

- '/2 inch 

- 20 Ibs/sq. ft. 

- .30 cal.,M2 AJ? 

- Army (pinhole) 


500 


1000 


1500 



2000 


100 

90 

80 

70 

60 

50 

40 

30 

20 

10 


2500 3000 

STRIKING VELOCITY 

feet per second 



September 1943 


















































































































WEAPON DATA 

PERFORATION OF HOMOGENEOUS ARMOR 
(BHN 250-300) BY UNCAPPED AP PROJECTILES 


<) G 7 ) 

jmk ARMOR 
PERFORATION 



2400 


SYMBOLS 

m * wgt. of projecti/expounds 
d - caliber of projectile,inches 
V, z perforation limit velocity, 
feet/second 
e - thickness of plate,inches 


e = PLATE THICKNESS 
inches 


THE GRAPH SHOWS THE RELATION BETWEEN PERFORATION LIMIT VELOCITY AND THICKNESS OF PLATE PERFORATED.THE LIMIT 
VELOCITY CONCERNED IS THAT AT WHICH THE PROJECTILE JUST PASSES COMPLETELY THROUGH THE PLATE (Novy Limit). 
THE DATA REPRESENT ARMOR PIERCING (A P) UNCAPPED PROJECTILES RANGING FROM 1.45 Inches TO 3.44 inches FIRED 
AGAINST HOMOGENEOUS ARMOR OF BHN 250 - 300 AT BOTH NORMAL INCIDENCE AND AN OBLIOUIT Y OF 30 DEGREES. 

BECAUSE OF INHERENT SCATTER OF THE DATA, THE RESULTS FOR EACH OF THE TWO ANGLES OF INCIDENCE ARE PRESENTED IN 
THE FORM OF A BAND. EACH BAND, THEREFORE, MAY BE LOOKED UPON AS SEPARATING TWO REGIO N S OF THE GRAPH, 
CORRESPONDING TO VULNERABILITY (above) AND SAFETY (below). 


EXAMPLES: 

AGiveno75mm M72 projectile 
^““striking at 30* obliquity witho 
velocity of 2000 ft./sec., two 
values of plate thicknesspbout 
3-3/8 inches and 3-7/8 inches, 
are read by following the line 
to each of the two borders of the 
bond. It isreosonable toassume 
that plate thicknesses greater 
than 3-7/8incheswil!besofe 
ogainst the g iv e n projectile , 
whi le t hi c k ne s s e s lessthan 
3-3/8 inches will be vulnerable. 


NOTE'. GRAPH INCLUDES DATA FROM THE NAVAL PROVIN G GROUND, DAHLOREN 


liSimilorly, for the given projectile 
J *(exomple A) f i re d at a pi a t e 
3-7/8 inches thick, two values of 
the striking velocity result by 
reading to the two borders ofthe 
band, namely about 2 000 ond 
22 30 ft./sec. The plate referred 
to islikelytobe safeagoinst 
striking velocities less than 
2000 ft./sec.arid vu Inerable 
to velociti e s gre ater than 
2 2 3 0 ft./sec. 


,VA., ANO THE DEPARTMENT OF NAT ION A L DEFENSE OF THE BRITIS H ARM V 




October 1943 











































































WEAPON DATA 




PERFORATION OF HOMOGENEOUS ARMOR 
(BHN 250-300) BY AMERICAN PROJECTILES 


16 18 20 "0 2 4 6 8 10 12 14 (6 18 20 

RANGE RANGE 

hundreds of yards hundreds of yards 

The above graphs show the thickness of homogeneous armor that can be expected to be perforated at 0° and 30° striking 
angles for various ranges by individual projectiles of known weight. The curves represent estimates based on data from 
actual firings or extrapolations of results of trials with other projectiles. 

For information on perforation of homogeneous armor by other projectiles, see Data Sheet 2 C3. 

SOURCE: Ballistic Section, Technical Division, Office of the Chief of Ordnance (U.S.). 


Ml,M2,M3 
M.v 2700 f/s 


3-IN.M62A1* 
M3,M5, 
M6.M7 
MV 2600f/s 


3HN. M79 
M3,M5, 
M6.M7 
M V 2600 f/s 


57mm M86 * 
Mt 

M.V. 2700 f/s 


75mmM61A1* 
M3.M4 
mv. 2030 f/s 


75 mmM72 
M3,M 4 
M.v 2030f /s 


37mmM5lB1 * 
M3A1, M6 
M.v. 2900 f/s 


40 mm M81A1 
Ml 

M.v 2870 f/s 


37 mmM 74 
M3A1 

M.v. 2900 f/s 


37mm M80 
M9 

M.v. 3050 f/s 


37mmM59 * 
M9 

M.V 2800 f/s 


20 mmM 75 
Ml, AN-M2 

M.V. 2615 f/s 


Cal .50 M2 
M1921A1 


CURVES FOR INDIVIDUAL AP AND APC PROJECTILES 

THICKNESS OF ARMOR 
PERFORATED inches 


THICKNESS OF ARMOR 
PERFORATED inches 


'/s 


V,o 


i/fe 


-Vio 


()° STRIKING ANGLE 7*0' 

Projectile listed above; gun below. 

* APC projectiles, others ore AP proj . 


( 




PERFORATION OF 
ARMOR-PROJECTILES 


40mm M81A1 
Ml 

M.V 2870 f/s 


37 mm M 74 
M3A1 

M v.2900f/s 


37mm M 80 
NTS 

M V 3050f/s 


37mmM59 * 
M9 

M v 2800f/s 


20mm M 75 
Ml, AN-M2 
M.v 2615 f/s 


Cal.50 M2 
M1921A1 
M2 H.B 
M.v 2935f/s 


57 mm M 86* 
Ml 

M.v. 2700 f/s 


75 mm M61A1* 
M3, M4 
M.v 2030 f/s 


75 mm M.72 

M3.M4 

M.V. 2030 f/s 


57mm M70 
Ml 

M.V. 2970 f/s 


90 mm M77 
Ml,M2, M3 
M V 2700 f/s 
3-IN.M62A1* 
M3,M5, 

M6, M7 
M.v. 2600 f/s 


3-IN M 79 
M 3, M5, 

M6, M7 
M.V. 2600f/s 


90 mm M 82* 
Ml, M2, M 3 
MV. 2650 f/s 


90mmM 82 * 
Ml,M2,M3 
M.v. 2650 f/s 


404 


PTM No. 112 
April 1945 
























































































































WEAPON DATA 

PERFORATION OF THIN HOMOGENEOUS HARD 
ARMOR BY SMALL CALIBER AP PROJECTILES 


Q G4 


J 

JMM ARMOR 
PERFORATION 



The graph shows the re 1 ation between perforation limit striking velocity (perforation limit range) and 
thickness of plate perforated for Caliber .50 M2 and Caliber .30 M2 AP projectiles fired against Horno- 
geneous Hard Armor of 8HN 350-450 at normal incidence and at an obliquity of 30°. The limit velocity 
concerned is that at which the projectile just passes completely through the plate (Navy Limit). Each 
value of limit velocity corresponds to a given range, depending on the M.V, of the gun. Range values 
for service muzzle velocities are given by the appropriate scales at each side of the chart. 


Because of inherent scatterof the data, results are presented in the form of a band and may be looked 
upon as separat i ngtwo regions of the graph: (a) "vulnerability" above and (b) "safety" below. The 0° 
band is drawn to include about 95% of the available firing data, while the 30° band includes 80% of 
the data for this angle. 


When thin Homogeneous Hard Armor in this Brinell range is used on aircraft, the limit velocity is con¬ 
siderably increased due to the tipping effect of the skin of the plane. The increase may amount to 
several hundred feet per second if the bullet is in a sidewise position when striking the armor. 

examples: 

A Given a Cal . 50 M2 AP projectile striking 
at 0° with a velocity of 2200 ft/sec, 
two values of plate thickness about 5/8 
in, and 3/4 in. are read by following the 
line to each of the two borders of the 
band. It is reasonable to assume that 
plate thicknesses greater than 3/4 in. 
will be safe against t he projectiIe , while 
thicknesses less than 5/8 in. will be vul¬ 
nerable. 



Similarly, for same projectile fired 
JA normally at a plate 5/8 in. thick, 
two values of striking velocity (or two 
pairs of range values, depending on M.V.) 
result by reading to the two borders of 
the band, namely a b ou t 2000 A. 2200 ft/sec or 700 
and 520 yd. or 760 and S 80 yd. The plate 
referred to is likely to be safe against 
striking velocities less than 2000 ft/sec 
(ranges greater than 700 or 7C0 yd.) and 
vulnerable to velocities greater than 
2200 ftisec (ranges less t han 5 20 or 580 yd .) 



BASED ON DATA FROM THE NAVAL RESEARCH LABORATORY, U S. NAVAL PROVING GROUND, BALLISTIC RESEARCH LABORATORY, AND WATERTOWN ARSENAL 


May 1943 


















































































WEAPON DATA 

PERFORATION 

OF HOMOGENEOUS ARMOR BY BOMBS 


<2 u si 

^■1 PERFORATION 

OF ARMOR: BOMBS 

V- 



The graph gives the relation between the striking velocity of a bomb and the th ickness of homogeneous armor which it will 
perforate. Due to inherent scatter of the data, the relationship is represented in the form of a band, and strikes at 
obliquities from 0° to 30° are included in it. 

EXAMPLE: Given a 1000-1b AN-Mk33 AP bomb striking with a velocity of 800 ft/sec; it can be expected to remain intact and 
to have a perforation limit thickness of 4^ to 6 inches of armor. 

SOURCE: 

Bureau of Ordnance, U .S .N. .Sketch Ho. 124400 revision B and Woolwich Bomb Report A4700, Research Dept, Woolwich, England 


♦ Revision of Data Sheet 2 C5, dated July 1944 


PTM No.100 


February 1945 






























































WEAPON DATA 


PERFORATION 

OF HOMOGENEOUS ARMOR BY BOMBS 

CURVES FOR INDIVIDUAL BOMBS BASED ON DATA SHEET 2-C5 

THICKNESS OF ARMOR 
PERFORATED, inches 



ALTITUDE OF RELEASE, 
thousands of feet 


C) (]lhx) 

Jtkd PERFORATION 

OF ARMOR: BOMBS 
V- -> 


The curves give the thickness of homogeneous armor, in a horizontal position, perforated by a bomb 
released from a plane in horizontal flight at a ground speed of 200 to 300 m.p.h. 

EXAMPLE: The dotted line indicates that in order to perforate 7 inches of armor the 1000-lb. AP bomb, 
should be released above 17,000 feet and the 1600-lb. AP bomb at an altitude above 12,500 feet. All 
other bombs are likely to break up on striking armor of this thickness. 

ACCURACY: Values read from the curves are estimated to be accurate to within 15%. 

SOURCE: "Selection of Bombs and Fuses to be Used Against Various Targets", OpNav-16-V # A6, Office 
of the Chief of Naval Operations, and Woolwich Bomb Report A4700, Research Dept., Woolwich, England 


August 1944 















































































































WEAPON DATA 

PERFORATION OF HOMOGENEOUS ARMOR 
BY TUNGSTEN CARBIDE CORED PROJECTILES 



2 I 

e = PLATE THICKNESS 


inches 

The chart shows the way in which limit velocity for complete perforation is related to thickness of homogeneous armor 
(BHN 220-330) perforated by capped and uncapped tungsten carbide cored projectiles striking at normal incidence and at 
30° to the normal. The data represent projectiles having cores ranging from 0.65 to 1.52 inches in diameter. Indicated 
on the nonogram scales are projectiles with cores standardized for field use. 

Because of inherent scatter of firing data, results are presented as bands. For each obliquity, the band was drawn to 
include 90% of the points. Capped and uncapped projectiles at 0° scatter randomly through the band; at 30° there is an 
evident separation as indicated. Tungsten carbide cores usually break up on impact. If there is complete disintegration 
of the core, perforation of 

example A 

Given an uncapped American 76mm M93 
projectile striking at 30°witha vel¬ 
ocity of 3200 ft/sec, two values of 
plate thickness, about 5 inches and 
64 inches, are read by following the 
line to each of the two borders of 
the band. It is reasonable to assume 
that plate thicknesses greater than 
% inches will be safe against this 
projectile, while thicknesses less 
than 5 inches will be vulnerable. 


SOURCE: Based on experiments 

PTM NO. 87 

January 1945 


the indicated thickness may not be attained. 



EXAMPLEB 

Similarly, for the same projectile (see 
Example Ajfiredat a plate about 5 in. 
thick, two values of the striking velo¬ 
city are read by following the line to 
each of the two borders of the band, 
namely 3200 and 2770 ft/sec. The plate 
referred to is likely to be safe against 
striking velocities less than 2770 ft/sec 
and vulnerable to velocities greater 
than 3200 ft/sec. 



by American, British and Canadian military establishments. 



408 












































































WEAPON DATA 
PERFORATION OF 

HOMOGENEOUS ARMOR BY GERMAN PROJECTILES 



(] 


1 


PERFORATION OF 
ARMOR: GERMAN PROJECTILES 


GUN 

PROJECT 

ILE 



THICKNESS 

OF H0M0GENE01 
at RAN 

IS ARMOR PERFORATED 
GES ,yards 

,inches 


Ca). 

mi a 

Model 

Type 

Weight 

pounds 

M.V. 

f/s 

100 

200 

250 

300 

400 

500 

600 

750 

800 

1000 

1250 

1500 

2000 

2500 

20 

KwK 30 

















’ \ 


KwK 38 

APshell 

0.327 

2625 

1.9 

1.7 


1.6 

1.5 











KwK 38 

AP40 

0.223 

3270 

2.2 

2.1 


1.9 

1.7 










28/20 

SPzB4I 

AP4I 

0.287 

4580 

3.7 

3.3 


3.1 

2.8 

2.6 

2.4 


1.9 






42/28 

Pak 41 

AP4I 

0.79 

4600 


4.5 




3.7 


3.2 


2.7 





37 

KwK 



















Pak(t) 

APshel1 

1.68 

2500 


2.2 



2.0 

1.9 

1 .8 









Pak(t) 

AP40 

0.79 

3380 

3.1 

2.8 


2.6 

2.3 










47 

Flak37 



















Pak(t) 

AP36 

3.64 

2540 

4.2 

4.0 



3.7 


3.5 


3.3 

3.0 





50 

KwK 

AP40 

1.95 

3440 



4.6 



3.9 


3.2 


2.6 


2.2 




Pak 38 

AP40 

1.95 

3930 



5.6 



4.7 


3.9 


3.3 

2.8 





Pak 38 

APC 

4.54 

2700 



3.5 



3.1 


2.7 


2.4 

2.1 

1.9 




KwK 

APC 

4.54 

2240 



2.6 



2.3 


2.1 


1 .8 

1.5 

1.4 



75/55 

Pak 41 

AP4I 


4123 






6.7 




5.9 


5.3 

4.6 


75 

KwK 42 

AP40 

10 

3674 






7.8 




6.7 


5.7 

4.8 

4.! 


Pak 40 

AP40 

9 

3250 



7.1 



6.7 


6.3 


6.0 

5.6 

5.3 

4.6 



KwK 42 

APCBC 

15 

3068 






5.9 




5.2 


4.7 

4.1 

3.6 

76.2 

Pak 36 

AP40 

9.25 

2800 


3.7 



3.4 


3.2 


2.9 

2.7 






Pak 36(r) 

APC 

16.7 

2430 






4.6 




4.1 


3.6 

3.1 

2.8 


Pak 36 

APCBC/HE 

14.33 

2200 


3.4 



3.2 


3.0 


2.9 

2.7 

2.6 

2.4 



88 

Flak 41 

AP40 

16.1 

3775 






10.0 




8.7 


7.6 

6.6 

5.7 


Flak 41 

APCBC 

22.45 

3400 






7.3 




6.9 


6.4 

6.0 

5.6 


Flak 36 

APCBC 

21 

2600 






5.1 




4.7 


4.3 

3.9 

3.5 


Pak 43 

APCBC 

22 

3280 
















Pak 43 

AP40/43 

16 

3775 















105 

F1ak 38-39 

APC 

57.4 











6.5 


6.0 

5.6 



K 18 

APCBC 

34.62 

2700 



6.7 



6.5 


6.2 


6.0 

5.8 

5.6 




K 18 

APCBC 


2370 



5.8 



5.6 


5.3 


5.1 

4.9 

4.8 




L FH 18 

APCBC 


1540 



3.4 



3.3 


3.1 


3.0 

2.9 

2.8 




L FH 18 

APCBC 


1280 



2.7 



2.6 


2.6 


2.5 

2.4 

2.3 



20 

KwK 30 



















KwK 38 

APshe11 

0.327 

2625 

1.2 

l.l 


l.l 

1.0 











KwK 38 

AP40 

0.223 

3270 

1 .9 

1 .8 


1.6 

1.5 










28/20 

SPzB4I 

AP4I 

0.287 

4580 

2.7 

2.6 


2.4 

2.2 

2.1 

1.9 


1.6 






42/28 

Pak 41 

AP4I 

0.79 

4600 


3.7 




3.0 




2.2 





37 

KwK 



















Pak(t) 

APshel1 

1.68 

2500 


1.7 



1 .5 

1.4 

1.3 









Pak(t) 

AP40 

0.79 

3380 

2.7 

2.4 


2.2 

1.9 










47 

Flak 37 



















Pak(t) 

AP36 

3.64 

2540 















50 

KwK 

AP40 

1.95 

3440 



3.3 



2.6 


2.1 


1.7 

1.3 





Pak 38 

AP40 

1.95 

3930 



4.3 



3.4 


2.7 


2.2 

1.7 





Pak 38 

APC 

4.54 

2700 



2.6 



2.4 


2.3 


2.0 

1.8 

1.6 




KwK 

APC 

4.54 

2240 


*• 

2.1 



1.9 


1.7 


1.5 

1.4 

1.2 



75/55 

Pak 41 

AP4I 


4123 






5.8 




5.1 


4.5 


3.9 . 

75 

KwK 42 

AP40 

10 

3674 






6.1 




4.8 


3.9 

3.2 

2.6 


Pak 40 

AP40 

9 

3250 

5.7 





5.0 




4.0 






KwK 42 

APCBC 

15 

3068 






4.8 




4.3 


3.9 

3.5 

3.1 

76.2 

Pak 36 

AP40 

9.25 

2800 



| 













Pak 36(r) 

APC 

16.7 

2430 




* 


3.7 




3.2 


2.9 

2.5 

2.2 


Pak 36 

APCBC/HE 

14.33 

2200 















88 

Flak 41 

AP40 

16.1 

3775 






7.9 




6.5 


5.4 

4.4 

3.7 


Flak 41 

APCBC 

22.45 

3400 






6.3 




5.9 


5.5 

5.1 

4.8 


Flak 36 

APCBC 

21 

2600 






4.3 




4.1 


3.7 

3.4 

3.2 


Pak 43 

APCBC 

22 

3280 

8.0 









6.5 


5.8 




Pak 43 

AP40/43 

16 

3775 

9.3 






i 



7.6 


6.7 



105 

Flak38-39 

APC 

57.4 











5.5 


5.1 

4.7 



K 18 

APCBC 

34.62 

2700 



5.7 



5.5 


5.3 


5.1 

4.9 

4.8 

4.4 



K 18 

APCBC 


2370 



4.9 



4.7 


4.5 


4.4 

4.2 

4.0 

3.7 



L FH 18 

APCBC 


1540 



2.9 



2.7 


2.6 


2.5 

2.4 

2.3 

2.1 

_ 


L FH 18 

APCBC 


1280 



2.3 



2.2 


2.1 


2.1 

2.0 

1.9 

1 .9 



>(>' 


}7>(Y 


ageneous armor (BHN from about 250 to 325) that is likely to be perforated at various ranges by German armor 
for striking angles of 0° and 30° (angle measured from line perpendicular to plate). Perforation values 
ther on actual firing data or on extrapolation of results of trials with other projectiles. It should be 


The table gives the thickness of homo 
piercing projectiles. Data are given 

in most cases are estimates based either on actual tiring 
noted that the tapered bore guns and the tungsten carbide projectiles (APHO and APg|) have only been in very limited production 

ABBREVIATIONS: Projectiles- Guns- 

AP Armor Piercing KwK 

APC Armor Piercing Capped Flak 

APCBC Armor Piercing Capped with Ballistic Cap Pak 


AP go Armor Piercing with Carbide Core 
AP g| Armor Piercing used in tapered bore gun 


Tank Mounted gun 
Anti-ai rcraft gun 
Anti-tank gun 

Pak(tl Anti-tank gun (Czech) 
r) Anti-tank gun (Russian) 


Pak ( 


FK 36 
S Pz B4I 
L FH 18 
K 18 


Field gun 

Heavy anti-tank gun 
Light Field Howitzer 
Med ium gun 


SOURCE: "Tactical and Technical Trends", No. 17; Cataloq of Enemy Ordnance Materiel, Office of Chief of Ordnance, U.S. A.; Proc. of the Ord. Bd. (Brit) 

PTMNo.39 February I9Y5 


CONFIDENT! Afi 


409 








































































WEAPON DATA 

PERFORATION OF MILD STEEL ARMOR 
(BHN 100-150) BY UNCAPPED AP PROJECTILES 


C>< 


o 

o 


mm MILD STEEL 
PERFORATION 



The graph shows the relation between perforation limit velocity and thickness of plate perforated. The limit velocity 
concerned is that at which the projectile just passes completely through the plate (Navy limit). The data represent 
armor piercing (AP) uncapped projectiles ranging from 0,30 inches to | .45 inches, and caliber 0.30 and caliber 0.50 
jacketed projectiles fired against mild steel armor BHN 100 - 150 at normal incidence. 

Because of inherent scatter of data, the results are presented in the form of a band. The band, therefore, may be 
looked upon as separating two regions of the graph, corresponding to vulnerability (above) and safety (below). 


EXAMPLES: 


A.Givena 37mm M80 projectile 
striking with a velocity of 
1600 ft./sec., two values of 
plate thickness about 1.6 in. 
and 2 inches, are read by fol¬ 
lowing the I ine to each of the 
two borders of the band.lt is 
reasonable to assume that plate 
thicknesses greater than 2 in¬ 
ches will be safe against the 
given projectile, while thick¬ 
nesses less than 1.6 inches 
will be vulnerable. 



IJ Similarly, for the given 
projectile (example A) fired 
at a plate 2 inches thick,two 
values of the striking velocity 
result by reading the two bor¬ 
ders of the band, namely about 
1550 and 1780 ft/sec. The plate 
referred to is likely to be 
safe against striking velo¬ 
cities less than 1550 ft/sec 
and vulnerable to velocities 
greater than 1780 ft/sec. 



SOURCE: 

Graph includes data from the Naval Research Laboratory, Bellevue, D. C., and the National Defense Research Committee, 
Princeton University. 


August 1945 

























































WEAPON DATA 

PEAK BLAST PRESSURE AS A FUNCTION 
OF DISTANCE AND WEIGHT OF EXPLOSIVE 



W 

WEIGHT OF EXPLOSIVE 
pounds 

10,000 — 


5,000 — 


1,000 — 


500 — 



10 - 


5 


I 


r P 

DISTANCE PEAK PRESSURE 

feet pounds per sq. inch 


10,000 


5,000 


1,000 


500 


— 0.08 

— 0.09 

— 0.1 


— 0.15 

— 0.2 

— 0.3 

— 0.4 

— 0.5 

— 0.6 

— 0.7 

— 0.8 

— 0.9 

— 1.0 


— 100 


— 1.5 


2 



- 10 



•— I 


— 3 

— 4 

— 5 

— 6 

— 7 

— 8 

— 9 

— 10 

— 15 
-20 

— 30 

— 40 

— 50 

= 100 

— 150 

— 200 

— 300 

— 400 

— 500 

= 1000 


Example showing 
use of nomogram 

w r P 



VALUES INDICATED ARE ESTIMATED ACCURATE TO ABOUT 25 PERCENT AND ARE AVERAGES OF A 
LARGE NUMBER OF MEASUREMENT^ ON A|LL TYPES OF B0MB£ AND ^EXPLOSIVES 
Note: Readings taken with the gauge 'side-on to the blast wave^ for'face-on" gauge, pressure values should be 
approximately doubled. 

June 1943 



411 











WEAPON DATA 

POSITIVE IMPULSE AS A FUNCTION 
OF DISTANCE AND WEIGHT OF EXPLOSIVE 

FOR TNT FILLED GENERAL PURPOSE BOMBS 


POSITIVE 

IMPULSE 


e) 


WEIGHT OF EXPLOSIVE (TNT) 

w, pounds 


10,000 - 


3,000 - 


1,000 


300 


3 

-I 

A 


1 

-j 

A 


too 


50 - 


10 - 


5 - 


I — 1 


IMPULSE 

I, Ib.millisec/sq. m. 


DISTANCE 

r, feet 


EXPLOSIVE FACTORS 
To obtain positive im¬ 
pulse for an equal wgt 
of a different explo¬ 
sive, multip 1 y final I, 
read from the nomogram, 
by: 

Torpex 
HBX 

Minol 2 
T ritonal 
Composition B 
(RDX/TNT- 60/40) 

TNT 

Amatol (50/50) 


I. 17 
1.15 
I. 13 
1.1 I 

1.08 


1.00 

0.88 


- 1,000 


300 


100 


30 


10 




- 05 


= 0.1 


- aos 


OX) I 


— I 


- 3 


-10 


- 50 


100 


500 


1,000 


Example showing 
use or nomogram 


250 


- 5,000 


*— 10,000 


43 


This sheet gives values of the positive impulse resulting from detonation of TNT-filled General 
Purpose (GP) bombs at ground level. Results refer to gauges placed side-on to the blast wave. 

The nomogram represents the empirical relation T _ 54 

-*■ “ r 

Where I is the positive impulse (1b-mi 11 isec/in 2 ) , based on pressure in excess of atmospheric , 
r is the distance from the explosion (ft) and w is the charge weight (lb). The constant in this 
equation is an average for American GP bombs. For other explosives, multiply final I, read from 
nomogram, by factors given in table; for other case weights (bomb types) use sheet 3A2a. 


so 


*Revised: August 1945 














WEAPON DATA 

BLAST IMPULSE DUE TO 

DETONATION OF BOMBS AT GROUND LEVEL 



BLAST 


A 2a 

POSITIVE 

IMPULSE 


This sheet gives information on the magnitude of the positive air blast impulse resulting from detonation of bombs near 
the ground. Impulse values are based on readings of gauges placed side-on to the advancing blast wave. 

The table gives a selection of impulse values for American bombs. 

BLAST IMPULSE FROM PARTICULAR BOMBS: Positive Impulse per Unit Area, lb-msec/in 2 



BOMS 

FILLING 

DISTANCE, feet 




20 

30 

40 

50 

60 

70 

80 

90 

100 

200 

300 

400 

500 

750 

1000 


100-1b 

TNT 

42 

28 

21 

17 

14 

12 

10 

9.2 

8.3 

4.2 

2.8 

2.1 

1.7 

1 .1 

0.8 


AN-M30 

Tritonal 

49 

33 

25 

20 

16 

14 

12 

1 1 

9.8 

4.9 

3.3 

2.5 

2.0 

1 .3 

1 .0 


250-lb 

TNT 

69 

46 

35 

28 

23 

20 

17 

15 

14 

6.9 

4.6 

3.5 

2.8 

1 .9 

1 .4 


AN-M57 

Tritonal 

82 

55 

41 

33 

27 

23 

21 

18 

16 

8.2 

5.5 

4.1 

3.3 

2.2 

1 .6 

I 

500-1b 

TNT 

117 

78 

58 

47 

39 

33 

29 

26 

23 

12 

7.8 

5.8 

4.7 

3.1 

2.3 


AN-M43, M64 

Comp.B 

128 

85 

64 

51 

43 

37 

32 

28 

26 

13 

8.5 

6.4 

5.1 

3.4 

2.6 


Tritonal 

138 

92 

69 

55 

46 

40 

35 

31 

28 

14 

9.2 

6.9 

5.5 

3.7 

2.8 

■J 

1000-1b 

TNT 



90 

72 

60 

51 

45 

40 

36 

18 

12 

9.0 

7.2 

4.8 

3.6 


AN-M44, M6 5 

Comp.B 



101 

81 

67 

58 

50 

45 

40 

20 

13 

10 

8.1 

5.4 

4.0 



TrItonal 



106 

85 

71 

61 

53 

47 

42 

21 

14 

1 1 

8.5 

5.7 

4.2 


2000-1b 

TNT 




119 

99 

85 

75 

66 

60 

30 

20 

15 

12 

8.0 

6.0 


AN-M34, M66 

Comp.8 




130 

109 

93 

81 

72 

65 

33 

22 

16 

13 

8.7 

6.5 



Tritona 1 




141 

118 

101 

88 

78 

71 

35 

24 

18 

14 

9.4 

7.1 

1 

annn-i h 

TNT 






205 

180 

160 

144 

72 

48 

36 

29 

19 

14 

iJ 


AN-M56 

Comp.B 






225 

197 

175 

158 

79 

52 

39 

32 

21 

16 



Tritonal 






243 

212 

189 

170 

85 

57 

42 

34 

23 

17 

p 

500-lb 

AN-M56 

TNT 


43 

32 

26 

21 

18 

16 

14 

13 

6.4 

4.3 

3.2 

2.6 

1 .7 

1.3 


1000-1b 
AN-M59 

TNT 



49 

40 

33 

28 

25 

22 

20 

10 

6.6 

4.9 

4.0 

2.6 

2.0 


Accuracy: It is estimated that the mean of a large number of tests will fall within 5% of the corresponding tabulated value. 


The positive impulse in air due to detonation of an explosive charge on the surface of the ground is given by 

I = E e s (^) i 

where : I = Positive impulse per unit area, Ib-millisec / in 2 . E = Explosive factor (values listed below). 

w = Weight of explosive, pounds. s = Equivalent cylinder charge/weight ratio 

r = Distance from explosion, ft. e = 2.718... = base of natural logarithms. 

The equivalent cylinder charge I weight ratio, S , is the ratio of the weight of charge to the total weight of an equiva¬ 
lent cylindrical bomb. An equivalent cylindrical bomb is defined to be one with the same weight of explosive as the ac¬ 
tual bomb, endosed in a cylindrical shell of the same material and with the same internal diameter and internal volume, 
closed at the ends, the thickness of the shell and ends being equal to the sidewall thickness of the actual bomb. 5 is 
given approximately by 


where 


5 = 


1 + 4I&J1 +. 

Dp, L 


rcp. 1 

8 w/D 3 \ 


t = Bomb case thickness, inches. 

D = Inside diameter of bomb body, inches. 


> for steel cased bombs fil¬ 
led TNT or Tritonal this 
becomes. 

P« 
P„ 


5 = 


1 + 


[IQ + 0.44 ] t 

w/ D 3 D 

Density of case material, lb/in 3 
Density of explosive filling, lb/m 3 


EXPLOSIVE FACTOR 

, E 

E x e 

Torpex 

35 

94 

HBX 

34 

92 

Mi nol 

33 

90 

Tritonal 

33 

89 

Ccw.B («g$M 

32 

86 

TNT 

29 

80 

Amatol 

26 

70 


* For uncased charges, where: 

S = 1 and I = E * e * (^) 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

Equivalent Cylinder Charge/Weight Ratio, S 


Ref: AES-4, *>51, (OSRD-4356) 
AES-7, P 9 , (OSRD-4754) 
August 1945 



_ ^ 


413 






















































































WEAPON DATA 

SIDE-ON AND FACE-ON BLAST PRESSURES IN AIR 


5 

versus 


A 5 

SIDE-ON 

FACE-ON 



The graph gives the relation between face-on pressure, Pf, recorded by a gauge fixed in an infinite rigid wall facing the 
blast, and side-on pressure, P $ , measured by a gauge whose face is parallel to the direction of motion of the blast wave. 

All pressures indicated are in excess of atmospheric pressure. 

This relationship is deduced from the Rankine-Hugoniot equations, assuming the incident blast wave to have a flat top. 
However, the curve will give the relation between the initial parts of the pressure-time curve obtained from an explosion, 
where P s is initial peak pressure in the oncoming wave (as given by a gauge side-on) and Pf is initial peak in the wave 
reflected from any finite object such as a gauge alone. 

If a side-on gauge were placed in front of an actual wall (i.e., one of finite extent and rigidity), and if another were 
set face-on in the wall, then the above relation would apply accurately to the initial phases of the blast pressure rec¬ 
ord obtained. However, if this relation were applied to the entire pressure-time curve it would predict face-on pres¬ 
sures that are too high at later stages of the record. The reason for the deviation is that the above formula does not 
consider any motion of the wall or diffraction of the wave around it. 


September 1943 


414 























































































































































WEAPON DATA 

IMPULSE DELIVERED TO A 

PLANE SLAB BY A CONTACT EXPLOSION 


i-1 

IMPULSE: 


o 


V4 


CONTACT EXPLOSIONS 


£ . IMPULSE, Ib-sec 
v ' CHARGE WEIGHT, lb 



The graph gives the total impulse delivered to an extended plane slab by detonation of a rectangular or cylindrical TNT 
charge in contact with it. For charges having either of the above forms, the impulse per unit weight can be correlated 
with the Shape Factor, A/A 2 , given by the plan area of the charge divided by the square of its greatest measurement per¬ 
pendicular to the slab (see sketches). 

Measurements were made by means of the impulse pendulum (see source reference). Charges used in the tests varied in weight 
from i to 2-lb, most weights being either 5 or I-1b. Approximately 75% of the measured impulse values lie within + 8 % 
of the empirical curve, which has the equation given in the graph above, where J is the impulse delivered to the plane 

slab (lb-sec), u> is the weight of charge (lb), A is the plan area of the charge and h is the maximum extension of charge 

perpendicular to the slab. All linear dimensions are measured in the same unit. A brief series of tests indicates that 
the values of J/w given by the above relation for TNT should be multiplied by the following factors for other explosives: 
Tetryl 1.6; HBX-2, Minol-2, Comp.C-3 1.2; Pentolite, Comp.B, Tetrytol, Tritonal, cast TNT I.I; Amatol 0.85. 
ror a charge having the form of a circular cylinder or a square-ended rectangular block, the ratio of the impulse deliv¬ 
ered when the charge is placed side-on to the slab to that with the charge set end-on is given simply by 

= JL( q + i) 

„„ 3 

end-on 

Here q is the Slenderness Index of the charge, conveniently taken to be the length/diameter ratio in the case of a cylin¬ 
der, or the length-to-side ratio for a square ended block (see sketches). The linear relation is a good approximation 
for q between I and 4 . 


SQUARE-ENDED BLOCKS 


END-ON 



Shape Factor, A/A 2 : s 2 /i 2 

Slenderness Ratio, q: l/s 


SIDE-ON 



Shape Factor, A/A 2 : l/s 

Slenderness Ratio, q: l/s 


CIRCULAR CYLINDERS 




SIDE-ON 


Shape Factor, A/A 2 : l/d 

Slenderness Ratio, < 7 : l/d 


Ref: AES-13 
September 1945 











































































































































































































































































































WEAPON DATA 

PENETRATION OF CONCRETE 
BY DETONATION OF CONE-END CHARGES 



A ft 

CONE-END 

CHARGES 


CONCRETE 


x- DEPTH OF PENETRATION,inches 



The graph shows depth of penetration produced in concrete by a cone-end charge placed with axis per¬ 
pendicular to the slab face. The mean line was determined by a least squares reduction; shaded band 
includes values 20% above and below mean. 


Because of scabbingon rear face (see inset sketches) perforation often results even when slab thick¬ 
ness is greater than the penetration depth that would result in massive concrete. 

TYPE OF EXPLOSIVE: Effects are not greatly dependenton explosive type provided charge is thoroughly 


compact 

BEST 

and adequately primed. 

- TNT/RDX Plastic H.E. 

GOOD - Pento1ite 

Nobel 808 

POOR - 60/40 Amatol 


TNT/PETN Cyclotol 

TNT 

Picric Acid 

P. A. G. 


TNT/CE P.E. 

Lyddite 

Tetrytol 



CONE LINING: Dependence on material and thickness is not great. 

Materials: BEST - Pressed steel. Forms large slug which may stick in hole, especially if cone 

angle is less than about 70°; may thus impair insertion of demolition charge. 
GOOD - Glass. Hole somewhat shallower but of larger volume than with steel. Less 
debris is left in hole. Cast brass and cast manganese bronze also good. 
Thickness: Various thicknesses used. Experiments i ndicate optimurn valueof about 0.1 inch (steel) 

for a charge of 6-inch diameter, and weighing approximately 10 lbs. 

CONE ANGLE: Not extremely critical, but 60° to 80° usually adopted. 

LENGTH-DIAMETER RATIO: Values of H/D (see sketches) between j and I are recommended. 

STAND-OFF DISTANCE: The optimum stand-off, S, appears to be between about { and li diameters. 

CONCRETE STRENGTH: In general, slightly larger but not deeper holes result in softer concrete. 

PILLBOX TESTS: Trials indicate that a 75-lb. charge will defeat a 5-ft. thick pillbox wall and throw 

scab capable of lethal or incapacitating effects on any occupants. 

DATA FROM EXPERIMENTS BY U S. ENGINEER BOARD AND BY BRITISH MINISTRY OF SUPPLY 


May 1944 


416 













































































































WEAPON DATA 

PERFORATION OF HOMOGENEOUS ARMOR 
BY WEAPONS WITH CONE-END CHARGES 


e) 


U> 


Inside Diameter 
Of Liner At Base 
d ,»n 


- 6.0 

r6.0 


“3x0^ 


i.O 


\ 


X 


X 


- 2.0 




-i.o 

-0.9 

- 0.8 

-0.7 


Thickness 
Perforated By 
Unrotated Charge 




Homogeneous 

Armor 


I. 0 -- 


-. 2.0 


Cone 

Angle a, 
degrees 

80-i 

70- 
60- 


2.C 


30- 
20 _ 

10 “ 


X 


3.0- 


4.0“ 


X 


X 


\ 


X 


6 . 0 - 


^“-0.0 

8,0 

9.Q-J-H0.0 
10 . 0 ' 


Mild 
Stee 1 
-I.o 


: "3.0 


1.0 


-- 8.0 


- - 6.0 

7.0 


- M ).8 

EXAMPLE: At normal incidence, an HEAT 105mm M67 having a 
forate about 5 in of armor, as shown by the index 


ARMOR 

PERFORATION BY 
CONE-END WEAPONS 


Thickness 
Perforated By 
Rotated Charge 
t, m 


ESTIMATED 
ACCURACY 
i 2b% 


Rotation Factor: 
use either 

# V 

or Muzzle Velocity 
V, ft/sec 
for rifling 
with twist of 
I in I in 
20: 32: 

o- 


Homogeneous 

Armor 

10 . 0 - 1 . 


9.0 

8.0 

7.0 

6 . 0-1 


n x d 

Rotational Speed, I 
n, rev/sec , times I 
Linear Diameter, I 

d, inches 

0 


10.0 

9.0 

— 8.0 
7.0 
6.0 




s.o-= 


3.0“ 


300-7 7(56 — 1100 
^SO 0^-1300 — 2100 
900 — —2000 -3200 


If cone axis makes an angle 9 with perpen¬ 
dicular to plate, multiply final thickness 
by the following factor: 


2.0 —- 


e 

I 0 6 

O 

O 

CNJ 

CO 

0 

0 

40° 

O 

O 

LT) 

K(=cos 0 ) 

0.98 

0.94 

0.87 

0.77 

0.64 


1.0 — 


Mild 

Steel 


5.0 
4.0 
*4.0 

—3.0 


2.0 


— 1.5 


muzzle velocity of 950 ft/sec and a twist of I in 20 will per- 
lines. At 30°, the performance will be about 5 x 0.87 = 4.3 m 


PERFORMANCE OF PARTICULAR WEAPONS: 

Thickness of Armor 


Weapon Perforated, in 

(normal incidence 
US - HEAT M6A3(Bazooka) 5.3 

Grenade M9AI 4.0 

HEAT 57mm T-20 E-2 3 

HEAT 75mm M 66 3.5 

HEAT 105mm M67 4.8 

Br - PI AT 3.8 

HEAT 3.7-in 4 95mm 5.0 

Ger- Panzerfaust 

(30, 60 4 100) 8.0 

Panzerschreck 

(Ger. Bazooka) 6.5 

Jap- A.T. Conical Hand 

Grenade 2.8 

A.P. Rifle Grenade 2 


The nomogram gives thickness of homogeneous armor perforated by Munroe jets 
from cone-end hollow charge projected weapons.The underlying empirical equa¬ 
tion, deduced from performance records on actual weapons is 


t 


o. 8q d cos 6 
sin( a/ 2 ) 


f(nd) 


where find) = l.0> 0.69, 0.5.7, 0.48, for nd - 0,300,600,900 r.t.s.x in 
respectively. (see notation on nomogram. I 

Factors such as thickness and material of liner, type and density of explo¬ 
sive, confinement of charge, stand-off distance, etc. are not included in 
the relation, although changes in these quantities are responsible for some 
variation in observed results. With the empirical relation used, scatter in 
the data precludes making a distinction between depth of penetration in mas¬ 
sive plate and thickness of plate perforated. Thus the present relationwill 
be useful in estimating performance of any weapon designed according to rea¬ 
sonable practice, but should be considered a rough guide to be used only in 
the absence of experimental data. 

Basic data are mainly for projectiles having steel liners and filled Cyclo- 
tol or Pentolite. Explosives combining high power with high rate of detona¬ 
tion give greatest target damage. As the equation above shows, rotated pro¬ 
jectiles generally form shallower craters; however, these are likely to be 
wider than the craters due to static detonation. 




Ref: 0TB-I2f (0SRD-535of) 
August 1945 






























































. 








































































WEAPON DATA 

MACH REFLECTION 




When a charge is detonated above ground a shock wave will spread out almost spherically as shown at A in the figure a- 
bove, which is a section in a vertical plane passing through the charge. As this shock wave, called the incident wave, 
strikes the ground it is reflected and the situation is somewhat as shown at B. If the ground were i nfin i te1yr i g i d and 
if the shock wave were weak (that is, almost a sound wave) the reflected wave could be constructed by imag i ning that the 
ground is replaced by air and an equal charge, the so called image charge, detonating at the same time at an equal dis¬ 
tance below the ground and in line with the actual charge. In an actual explosion the reflected wave differs from the 
one constructed in this manner, primarily because the incident wave is stronger than a sound wave. 

The angle between the normal to the wave front and the normal to the ground surface is called the angle of incidence. It 
has been found that for each ratio of the pressure in front of the shock wave to that immediately behind the wave front 
there is a critical angle of incidence beyond which reflection of the type shown at B is impossible. Thus there is some 
place along the ground where a new type of reflection called Hach reflection takes place. A new wave, called the Mach 
wave, is formed and the situation is as illustrated at C, D and E in the figure. The intersection of the incident wave, 
the reflected wave, and the Mach wave is called the triple point. 


As the phenomenon progresses the Mach wave grows and the triple point describes a curve through the air. This path has 
been-studied in detail experimentally and a typical path is shown in the figure above. Other paths are shown in the low¬ 
er figure of sheet 3 A8. 


As the Mach wave grows in height it absorbs the 
incident and reflected waves. Ultimately, at 
distances very large compared to the height of 
burst, the whole configuration of shocks becomes 
approximately a single spherical shock wave in¬ 
tersecting the ground orthogonally. 

The pressure and impulse at a point which is a 
horizontal distance d from the charge & a height 
H above the ground go through a maximum as the 
height of burst h of the charge is varied. The 
height of detonation which maximizes these quan¬ 
tities at a point (d,H) is that which creates a 
triple point passing approximately through (d,H). 

The height of burst which maximizes the pressure 
and impulse at a point along the ground at a hor¬ 
izontal distance d from the charge is the height 
for which Mach reflection just forms at the poi nt 
in question. The relation between d and h for 
beginning of Mach reflection is given in the 
graph in terms of the scaled variables d/w a & 
h/u 1/a where u> is the weight of charge. 



d _ Horizontal Distance From Charge, ft 
u» l-/ 3 \/Charge Weight, pounds 


Ref: AES-I, NDRC Report A-320 
August 1945 


419 

























































WEAPON DATA 

OPTIMUM HEIGHT FOR MAXIMUM IMPULSE 







MAXIMUM 


1 ° 

Ao 

HEIGHT FOR 
IMPULSE 




J 



As the height of detonation of a charge is varied the positive impulse at a fixed horizontal distance d and height above 
ground H goes through a maximum whose value is denoted by I ajf . The values of I J 7 m ./u ; 1/3 as a function of d/w' 3 are 
plotted in the upper figure for several fixed H /w 1 ' 3 . The height of detonation of the charge which will maximize the im¬ 
pulse at a point (d,W) i s the one which will produce a Mach reflection whose tripie point passes approx imately through the 
point (d, HL For convenience the impulse on the ground due to a charge detonated on the ground is also given in this 
figure. In the lower figure each curve is a path of the triple point for a fixed value of h/ui 1/3 where h is the height 
of detonation of the charge. 

The graphs may be used to determine the height of detonation necessary in order to maximize the horizontal distance at 
which a given level of impulse is formed at a height H above the ground. For example, suppose that a building 40 feet 
high is to be attacked and that a positive impulse of 90 1b-mi11isec/in 2 is necessary to accomplish the desired damage. 
The impulse should have its maximum at half the height of the wall, so the value of H is 20 feet. Assume that a 4000-lb 
LC bomb filled Comp. B is to be used; it is found from Sheet 3A2a that this is equivalent to 2760 pounds of bare TNT so 
w 1/3 for use in the graphs above is 14. Then I/u/'s is 6.43 and H/w 1 ' 3 is 1.43. From the upper figure we find that d/w 1 ' 3 
is 13.9 and using this value we find from the lower figure that h/w 1 ' 3 is 4. Thus the bomb should be detonated at a height 
4 x 14 = 56 feet above the ground, and the maximum distance at which damage can be achieved is 13.9 x 14 = 195 feet. From 
the dashed curve in the upper figure we find that if the charge had been detonated on the ground the impulse level of 
90 1b-mi11isec/in 2 would have been reached at 155 feet. Thus in this case the airburst increases the radius of damage 
from 155 to 195 feet, and increases the area over which damage can be achieved by about 58%. The example is shown by 
dotted lines on the graphs. A change in height of burst of 40% from the optimum height will change the impulse at a 
point (d, H;, from l max by 10%. 


Ref: AES-3; AES-9c 
August 1945 




























































































WEAPON DATA 

PRESSURE AND IMPULSE ON THE GROUND 
DUE TO EXPLOSIONS IN AIR 



A 9 

HEIGHT EFFECT: 


PRESSURE & IMPULSE 



The curves show the peak blast pressure P and the positive blast impulse I as measured by gauges set flush with level 
ground at a horizontal distance d from a bare charge of w pounds of THT detonated at a height h above the ground. The 
pressure curve labeled "0" is obtained from measurements of pressure from a charge detonated in open air on the assump¬ 
tion that the pressure from w pounds detonated on the ground is equivalent to that from 2u> pounds detonated at the same 
distance in open air. The other curves are based on tests using £-lb bare TNT charges, experiments using mechanically 
produced shock waves, and deductions from the theory of regular reflection. 

To find the height at which a charge should be detonated to yield maximum peak pressure or positive impulse, at a given 
distance d , read upward from the proper value of d/u 1 '' 3 to the curve that is highest at that point and take the value 
of h/v 1 '» for that curve. To find the height of detonation that will yield a given peak pressure or positive impulse at 
the greatest distance, read horizontally from the appropriate value of P oc I/w 1/s to the curve that lies farthest to 
the right and take the value of h/v 1 '* for that curve. 


Ref: AES-I; AES-2 
August 1945 







































































































































































WEAPON DATA 


CRATERS IN SOIL: DIAMETER AND DEPTH 


o 


Ma 


CRATERS: 
DIAMETER AND DEPTH 


CRATER DIAMETER, D 



The corves give the mean value of crater diameter and apparent crater depth for charges detonated in clay, loam, or'sand 
as a function of the depth of the center of the charge below the surface of the ground; negative values of depth are in¬ 
cluded, corresponding to detonation above ground. Deviation between mean and observed values may be as much as 30%. 


The curves are for TMT. Craters due to composition B or Amatol 50/50 are not significantly different. Tritonal forms 
craters approximately 10% larger than given by the curves. HBX and Minol form craters approximately 15% larger. 


EXAMPLE: The dotted line indicates that a 1000-Ob charge detonated at a depth of 8 feet will form a crater 51 feet in 

diameter and 14 feet in apparent depth in clay. 

TYPICAL CRATER PROFILES showing apparent 
depth, diameter, and posit ion of charge. 

A: Bomb at moderate depth, clay or loam 
B: Bomb at or above ground, any soil. 

C: Bomb below ground surface, dry sand. 


* Revised: 
August 1945 





422 













































































































WEAPON DATA 


CRATERING BY LINE CHARGES 


o 


Mb 


CRATERING 
BY LINE CHARGES 


The width of crater D, in feet formed by explosion of a line charge on various soils is given by the following empiri¬ 
cal relations, where w is the linear charge weight in pounds per foot. 


Type Soil 

Average Crater Width 

D. feet 

70% of Crater 
Widths Fall Between 

Loose Dry Sand 

D = 3.7 VV 

S-OV^" and 4.4V*<T 

Packed Wet Sand 

D ' 2.6V 1 w 

2.1 */w and 3.\^uT 

Fine Sandy Silt Loam 

D = 3.2 *fw 

2.6 >fw and 3.9V%3~ 

Sandy Clay Loam 

D = 2.6VT7 

2.0 yfuT and 3.4V^* 

Wet Rich Clay 

D = 2.IVTT 

1.5and 2.8-v^* 


Crater widths for line charges exploded under water are greater than those listed here. 


CRATER WIDTH , D, feet 

20 ■---r 



LINEAR CHARGE WEIGHT, w, pounds per foot 

The graph shows the relation between linear charge weight, 
w, in lb/ft and the width of crater, D, in feet formed by 
detonating line charges on various soils* This width is 
measured between the shear shoulders of the crater as shewn 
in the sketch. 

The lines which are drawn are based on the average of a large number of tests. It is expected that a majority (70%) of 
craters will differ from the average by less than 25%. A minority (30%) of the shots will show extreme variation. Ex¬ 
plosives tested include C-2, Amato), TNT and liquid explosives. Variation in crater width is attributed chiefly to soi1 
conditions; effect of different explosives is masked by this variation. 

Example: The M-3 snake (14- lb/ft) produces craters which should average m feet across in dry sand; 12 feet in fine 
sandy silt loam, feet in sandy clay loam or packed wet sand, or 7$ feet in wet rich clay. 



Source: Tests by Engineer Board, U.S. Army: and by Joint Army-Navy Experimental Testing Board, U.S. 


Ref: AES-13 
August 1945 




















































































WEAPON DATA 

EARTH DISPLACEMENTS 

DUE TO UNDERGROUND EXPLOSIONS IN CLAY SOIL 

Data taken from British experiments on detonation of bombs and American experiments with bare 



Charges . 


u = SURFACE — - SURFACE DISPL. Vnches) 

DISPLACEMENT ” "f /CHARGE WT. ( pounds) 


[inches) 



The curves show horizontal and vertical displacements of the surface of the ground measured at various distances from the 
exploding charge. The phenomena obey a model law, so that results for different weights of charge may be represented on 
the same curve. 


SOIL EFFECT: Values given are from observations on clay and clay-gravel mixture. Displacements in chalk, not shown on 
this plot, were found to fall below those in clay. 

TYPE OF EXPLOSIVE: The curves are based on experiments using the following types of explosives: T.N.T., 40/60 Amatol, 
Baratol, Dithekite, Minol, Black Powder and Dynamite, with charge weights ranging from 2.5 to 990 pounds. On the other 
hand, displacements in clay obtained with Torpex and Hexanite are greater than for equal weights of any of the above ex- 
PI os i ves . 

ABSENCE OF DEPTH EFFECT: The data indicate that for the range of deptns tested, the displacements obtained are independ¬ 
ent of the depth of burial L provided only tnat the bomt or charge is completely buried. Depths in tnese experiments va¬ 
ried from 7 to 22 feet, and the corresponding values of L/W * ^ ® were between l.l and 3.6 ft/lb 1 ^. 

ACCURACY OF GRAPH: The curves predict displacements over the entire range with an average deviation of 15%. 

EXAMPLE: Dotted line indicates that a 1000-lb. charge produces a transient vertical displacement of 6 inches at 50 ft. 


November 1943 




















































































































































WEAPON DATA 

PEAK PRESSURE 

AND IMPULSE DUE TO EXPLOSION IN EARTH 




The nomograms yield values of peak pressure and positive impulse in free earth due to detonation of based charges of TNT 
and bombs filled 50/50 Amatol. The equations are based on tests for the U. S. Engineers, and extensive small scale tests. 
In these tests the charge was buried at the depth giving maximum crater diameter (2.1 w^ 3 ). ft and pressure and impulses 
were measured at the same depth. Under different geometrical conditions the values of pressure and impulse will differ from 
those given here. With gauges at a constant depth, variations in the charge depth between about 0.7 and 5 u> v s ft ap¬ 
pear to produce negligible change in pressure and impulse values. On the other hand for fixed charge depth alteration of 
the gauge depth causes appreciable change in pressure measurements, there being a general increase with depth. Values of 
k for typical soils are computed from the velocity of seismic waves in the subsurface material. Actually k depends on many 
factors and ranges designated for various soil types should be considered a rough guide only. For explosives other than 
TNT, final values of pressure or impulse read from nomogram should be multiplied by the factors tabulated above. 

Pressures measured at the surface of a buried massive target are found to be about twice the free earth values given by the 
nomograms. Impulse values are approximately 2.5 times the free earth Values. 

EXAMPLE: The dotted lines indicate that at a distance of 20 ft from a 267-lb charge of TNT the maximum free earth pressure 
in clay loam will be about 100 lb/in 2 and the impulse about 1.4 Ib-sec/in 7 . 


Ref: PTM No. 93 
‘Revised: September 1945 























WEAPON DATA 

PEAK PRESSURE 

AND IMPULSE DUE TO UNDERWATER EXPLOSIONS 

Data supplied by the Underwater Explosives Research Laboratory, Division 8, NDRC. 


e) 


Cl 


UNDERWATER 

PRESSURE-IMPULSE 


DISTANCE FROM 
CHARGE 
r, feet 


PEAK 

PRESSURE 
P, tb/in* 


POSITIVE IMPULSE 
to t = 80 
I, tb.sec/in e 


100 

90 

80 

70 

80 

90 

40 

90 


go- 


10 

9 

8 

7 

6 

9 


400 - 

900 
800 

700 H 
800 
900- 
1000 - 


£000 

5000 

4000 

9000 

8000 

7000 

8000 

9000 

10,000 


£ 0 , 000 - 

50,000- 

40,000- 
90,000- 
80,000 


0.1 


0 .£ 


0.5 

0.4 

0.9 

0.8 

0.7 

0.8 

0.9 

1.0 


£.0 


5.0 

4.0 

9.0 

8.0 

7.0 

9.0 

9.0 

10.0 


-too 

-50.0 

-40.0 

-90.0 

-80.0 


WEIGHT OF 
CHARGE 
w, tb 
r tO 


50 

40 

90 

80 

70 

80 

90 

100 


325-lb DB,AN-Mk 41' 
325-lb DB,AN-Mk 17-2 
500-lb GP, AN-M64' 


650-lbDB,Mk 38- 
650-lb DB.Mk 29,37- 

1000-lb GP ,AN*M65 — 


2000-lb GP.AN-M66 —! 


200 


- 500 


400 

900 

800 

700 

800 

900 

1000 


£000 


t- 5000 


The nomogram yields va1ues of underwater peak pressure and pos i tive impulse due to detonation of charges 
of cast TNT. Values corresponding to THT-fi1 led American depth bombs and GP bombs accommodating hy¬ 
drostatic fuses are indicated on the charge weight scale. Peak pressure measurements on the fo1 Iowing 
explosives range from 15$ to 20$ higher than for TNT: DBX, Minol, D8Y, Special DBX, DBU, Torpex,— 
the values increasing in the order given. 

The scales correspond to the following empirical equations based on a large number of measurements: 


20,400 


'/5 \ 1.14 


l tb.S0c^n* - 1,50 




Vs 


Gauges were located in the equatorial plane of the charge and were placed "side-on" relative to the 
oncoming wave. Average deviation of values obtained from different gauges is of the order of 3$ - 5$. 

The sketch shows a typical pressure-time record. Since the tail p,/A/W* 

portion of such a curve decreases very slowly, it is necessary 
to measure I to a chosen point in order to obtain a definite 
value. This limit has been chosen as t = 80 , where 0 is the 
time constant of a decreasing exponential function which fits 
the initial part of the curve. Absolute values of impulse may 
be inexact by as much as 15$. 


4000 


5000 


2000 


IOOO 



TYPICAL p-t RECORD 


experimental curve 
p • Pe' t/ * 


t 


1.0 


1.9 mstc 


EXAMPLE: 


At 50 feet a 650-lb Mk 38 depth bomb (charge weight ■ 425 lbs.) produces a peak pressure 
of 2400 lb./in 2 , and a positive impulse of about 1.7 lb. sec./in 2 . 


April 1944 













WEAPON DATA 

MAXIMUM RADIUS OF BUBBLE OF BURNT GASES 
FROM AN UNDERWATER EXPLOSION 


7 :> 

BUBBLE 



UNDERWATER 

RADIUS 


WEIGHT OF 
CHARGE, 

pounds 

DEPTH OF CHARGE, feet 

2 

3 

5 

8 

10 

15 

20 

25 

30 

40 

50 

75 

100 

0.1 

1 .8 

1 .7 

1.7 

1.7 

1.6 

1 .6 

1.5 

1.5 

1 .4 

1 .4 

1.3 

1 .2 

l.l 

0.25 


2.4 

2.3 

2.3 

2.2 

2.2 

2.1 

2.0 

2.0 

1 .9 

1.8 

1.6 

1.5 

0.5 


3.0 

2.9 

2.9 

2.8 

2.7 

2.6 

2.5 

2.5 

2.3 

2 2 

2.0 

1.9 

0.75 


3.4 

3.3 

3.2 

3.1 

3.0 

2.9 

2.8 

2.7 

2.6 

2.3 

2.2 

1.00 


3.7 

3.6 

3.6 

3.4 

3.3 

3.2 

3.1 

2.9' 

2.8 

2.6 

2.4 

2.00 


4.7 

4.5 

4.5 

4.3 

4.2 

4.0 

3.9 

3.7 

3.6 

3.2 

3.0 

3.00 


5.2 

5.1 

4.9 

4.8 

4.6 

4.5 

4.2 

4.1 

3.7 

3.4 

5.00 


6.2 

6.1 

5.8 

5.6 

5.5 

5.3 

5.0 

4.9 

4.4 

4.0 

7.5 


7.1 

7.0 

6.7 

6.4 

6.3 

6.1 

5.8 

5.5 

5.1 

4.7 

10. 


7.8 

7.7 

7.4 

7.1 

6.9 

6.7 

6.4 

6.1 

5.5 

5.1 

15. 


8.8 

8.4 

8.1 

7.9 

7.6 

7.3 

7.0 

6.3 

5.9 

20. 


9.6 

9.3 

9.0 

8.7 

8.4 

8.0 

7.7 

7.0 

6.4 

25. 


10. 

9.7 

9.4 

9.1 

8.6 

8.2 

7.5 

6.9 

30. 


II. 

10. 

10. 

9.6 

9.2 

8.8 

8.0 

7.4 

40. 


12. 

II. 

1 1. 

11. 

10. 

9.6 

8.8 

8.1 

50. 


13. 

12. 

12. 

1 1. 

1 1. 

10. 

9.5 

8.8 

60. 


13. 

13. 

13. 

12. 

12. 

1 1 . 

10. 

9.3 

70. 


14. 

14. 

13. 

13. 

12. 

12. 

1 1. 

9.8 

80. 


14. 

14. 

13. 

13. 

12. 

II. 

10. 

90. 

_/■ . \_ 

15. 

14. 

14. 

13. 

13. 

12. 

11. 

100. 


CALCULATED BUBBLE 
RADIUS FOR TNT, feet 

To estimate radius for 
other explosives multi¬ 
ply value in table by: 

1 .07 for tetryl 
1.21 for torpex 

L J 


15. 

15. 

14. 

14. 

13. 

12. 

II. 

150. 



18. 

17. 

16. 

16. 

15. 

14. 

13. 

200. 



19. 

19. 

18. 

17. 

16. 

15. 

14. 

250. 



20. 

19. 

19. 

18. 

16. 

15. 

300. 



21. 

21 . 

20. 

19. 

17. 

16. 

400. 

_/" ___ 

23. 

23. 

22. 

21. 

19. 

18. 

500. 


WEIGHT CONVERSION TABLE 
pounds grams 

0.1 = 45.4 

0.25 - 113.5 

0.5 = 227. 

0.75 = 340.5 

1.00 = 454. 


25. 

23. 

22. 

20. 

19. 

750. 



28. 

27. 

26. 

23. 

22. 

1000. 



29. 

28. 

26. 

24. 

1500. 



34. 

32. 

29. 

27. 

2000. 



37. 

36. 

32. 

30. 

4000. 


45. 

41 . 

39. 


The table gives the maximum radius of the bubble formed by burnt gases from an underwater explosion and is based on the 
equation given below. 

where: R = maximum radius, feet 

h = constant dependent on explosive charge = 12.2 lb 1/3 ft 4 ^ for TNT 
w = weight of charge, pounds 
h = depth of charge, feet 
h 0 = atmospheric head = 33 ft 

This equation is derived theoretically in NDRC Report C4-sr20-0l0. The constant k was determined from the relation between 
the period of pulsation and the radius which is given in the above report and in the Applied Mathematics Panel Report 37.1 R 
and from measurements of the period at the Underwater Explosives Research Laboratory. The table has been checked at one 
point by direct measurement of the bubble radius. 


R = k 


w 


(h ♦ hj 


January 1945 



















































































































































































































































































-• 





























































































































































WEAPON DATA 

IMPULSE CRITERION-DAMAGE LEVELS 


0 


U) 


£ 

MPULSE 


DAMAGE LEVELS 


Damage to buildings of wall bearing construction has been divided into the following categories: 


A Damage: 
B Damage: 

C Damage: 
D Damage: 


Buildings completely demolished. 

Damaged beyond repair and requiring demolition. If one fourth of the wall area is destroyed, 
the entire building is said to suffer 8 damage. 

Seriously damaged and requiring repair before being used. 

Still habitable, but requiring repair. 


The mean radius and maximum radius of each level of damage due to blast has been estimated as follows: From one inci¬ 
dent the value of the maximum radius of damage of a given level is obtained by measuring the distance between the bomb 
and the furthest point of the furthest building suffering that degree of damage. Averages over a number of incidents of 
such radii for German instantaneously fuzed bombs against British wall bearing construction are given for various sizes 
of bombs in REN 214 revised. 


The mean radius of a given level of blast damage from a bomb is determined as the radius of the circle with the bomb as 
center which Includes as many buildings which do not suffer the specified degree of damage as there are damaged build¬ 
ings excluded. For a number of incidents one averages the areas so obtained. The radius of a circle with the average 
area is then the average mean radius. Such radii are also listed in REN 214, revised. 

The mean and maximum radii of a given level of damage are found to be proportional to w 2/ a where w is the weight of ex¬ 
plosive in the bomb in pounds, for bombs wh ich are not too large (less than 3500 lb. of explosive). The constant of pro¬ 
portionality depends on the level of damage as well as on the explosive used, case weight, etc. The distance from a 
bomb with w pounds of explosive at which a given level of positive impulse is obtained also is proportional to iv 2/ 3. This 
suggests that a correlation exists between impulse and damage. (This correlation is supported by theoretical arguements 
to be found inR.C.349). The table below gives the relation between radii of damage and impulse levels, found to exist 
for British construction. 


IMPULSE LEVELS FOR 
Instantaneous 

BRITISH CONSTRUCTION 

Fuzed Bombs 

2 

I, Lb-tnilLisec/in 

Mean radius, A Damage 

120 

Maximum radius, A Damage 

90 

Mean radius, B damage 

72 

Maximum radius, B Damage 

54 

Mean radius, C Damage 

40 

Maximum radius, C Damage 

30 


IMPULSE LEVELS FOR GERMAN CONSTRUCTION 
(Damage Determined by Photocover) 


Instantaneous Fuzed Bombs 


I, lb-millisec/in' 


Mean radius, demolition 
Maximum radius, demolition 
Mean radius, visible damage 
Maximum radius, visible damage 


120 

90 

55 

40 


Also listed in the table are the categories of damage applied to photo-cover of results of Allied bombing of German wall 
bearing construction. It was found that the categories of damage A, B, and C could not be distinguished on photo-cover 
and two categories, demolition and visible damage were introduced. Since German construction is heavier than British, it 
is to be expected that the impulse level corresponding to a given degree of damage such as A, B, or C would be increased; 
the amount of increase is given to a first approximation by the ratio of wall thicknesses. Thus, the mean radius of B 
damage against German construction is expected to correspond to an impulse level of 108 lb-mi 11isec/sq.in. The radius 
of demolition is thus between the radii for A and B damage whereas that for visible damage is slightly larger than the 
radius for C damage. 


The departure of the area of damage from a circle is reflected in the large difference between the maximum radius of a 

given level of damage and the mean radius. The reason for this is that because of the bui lt-up-ness of the target there 

is shielding of the blast. The evidence indicates that on the average this shielding can be taken into account by decreas¬ 
ing the maximum radius of a given category of damage by 25% to obtain the mean radius (since impulse is inversely propor¬ 
tional to distance). 

Theoretical considerations and operational data show that the impulse criterion does not hold for very large blast bombs. 
The weight for which it no longer applies depends on the type of construction. For British and German construction the 
radius of a given level of damage from bombs having between 3500 and 8000 lbs. of explosive is proportional to For 

considerably larger bombs it becomes proportional to w 1 ^. The latter is the same as the dependence of the distance for 
a given level of peak-pressure on the weight of explosive. This is reasonable since as the weight of explosive increases 

the duration of the blast at a given point increases and so does the impulse; however, the walls of the building will 

not fail under blast loading with large impulse unless the practically constant pressure (which occurs in this case) is 

above the static strength of the walls. (See R.C. 349). 

Using the relation given in sheet 3 A2* for impulse due to explosions on the ground, values of the radii for A, B.and 0 

damage due to different bombs have been computed. Results are given in the table below. 


Bomb, Instantaneous Fuzing 

Mean Radius 

A Damage, ft 

Mean Radius 

B Damage, ft 

Mean Radius 

C Damage, ft 

100-1b GP AN-M30, TNT filled 

7 

12 

21 

100-1b GP AN-M30, Tritonal filled 

8 

14 

25 

250-lb GP AN-M57, TNT filled 

12 

19 

34 

250-lb GP AN-M57, Tritonal filled 

14 

23 

41 

500-lb GP AN-M64, TNT filled 

20 

33 

59 

500-lb GP AN-M64, Comp. B filled 

21 

35 

64 

500-lb GP AN-M64, Tritonal filled 

23 

38 

69 

1000-1b GP AN-M65, TNT filled 

30 

50 

90 

1000-lb GP AN-M65, Comp. B filled 

34 

56 

101 

1000-1b GP AN-M65, Tritonal filled 

35 

58 

105 

2000-lb GP AN-M66, TNT filled 

50 

83 

ISO 

2000-lb GP AN-M66, Comp. B filled 

54 

90 

162 

2000-lb GP AN-M66, Tritonal filled 

59 

99 

177 

4000-lb LC AN-M56, TNT filled 

119 

200 

360 

4000-lb LC AN-M56, Comp. B filled 

131 

220 

395 

4000-lb LC AN-M56, Tritonal filled 

142 

236 

425 


September 1945 






































WEAPON DATA 

BLAST DAMAGE TO STEEL COLUMNS 


(i A la 

STEEL 

COLUMNS 


INDEX OF COLUMN a 
SLENDERNESS AND XI 
ASPECT b'L 


0.014 


0.012 


O.OK) 


0.008 


0.006 


0.004 


0.002 


X 


TX 


A ASPECT ^ 

web approximotely 
in line with blast 



1) ASPECT 
web approximately 
transverse to blast 



DEFINITIONS 

A, - orea of site! cross- section , sq inches 
L - cleor height of column , inches 

b - horizontal dimonsion of column expotad 
to blast, inches 

t - distance from center of column to the 
center of explosion, feel 
w - chorge weight of explosive, pounds 


8 10 
DISTANCE FROM B0M8 feet 

CHARGE WEIGHT pounds 


CHG.WT. 266 lb. 

1000 lb. SAP AN-M59 

k9. . 

■ a > . . . . f , 

'P 


> - ■ ■ ■ . . i ■ . . ■ -i- . . . 

20 30 

♦p . 


1 . . . 

50 

■ r . 


, i . i . . r . 

. «P. 


CHO. WT. 308 lb. 

1000- lb. 6. P. AN-M44 

r 

fc ? 

....... ¥>. . • • 


20 30 40 

5p. . 

a a J . 

60 


» - - - 

■ 7 .° 

8 ,°, 

CHG.WT. 538 lb 

2000- lb. G.P. AN-M34 

r 

k ? 

..'P. 

,2p, 

.v. ...... .«P.3° .. 

..... .¥>. ..... 

, 7 i°, 

. - - i . . . 

®,°, 


o 

or 

ipo 

CHG.WT. 1077 1b. 

4000-lb. LC AN- M 56 

V 

b ? 

. JP.*P. 

, 3° 

.3?.6°. 

qo 90 

!po 

.......'I?. 


120 

. .!*> ... wp 


CHG.WT. 3245 lb. 

f 






DISTANCE 

FROM BOMB 

feet 


The curves define approxineteIy the limiting dis¬ 
tances from var I ous bombs at which stee I columns will 
be damaged Indifferent ways: blown out or severed, 
damaged beyond repair a 11hough not b I own out, or not 
damaged critically. The widthofthe bands is com¬ 
puted on the assumption of reasonable variations in 
the shape of a cross-section designed to carry a 
given load. The column Index, plotted vertically, 
is the ratio of the steel .cross-section of the 
column to the area exposed to the blast. This area 
is the product of the length of the column and its 
projected widthona line perpendicular to the line 
joining the column to the bomb. This index is re¬ 
lated to the ratio of the radius of gyration of the 
cross-section to the length of the column; i.e. 
large values of the index correspond to stubby 
columns and small values to slender columns. 

The columns are assumed to have no partitions or 
walls attached and to be exposed to blast on all 
sides. If there are partitions attached to the 
columns the rad I us of damage Is likely to be great¬ 
er, since part of the force on the attached elements 
is transmitted to the columns. Further, in such 


cases the blast wave cannot so readily make its 
way around the column to back it up from behind. 
On the other hand,where the column is supported 
by a partitionora wall approximately in line with 
the blast wave, the radius of damage should becon- 
s i der abIy smaller. 

As shown by the curves, the radius of damage is 
considerably reduced when the bomb is situated 
approximately in line with the web of the column 
(aspect A). For bombs drooped at random in an or¬ 
dinary building, about 75 - 80} of the cases of 
damage will be those in which the web is more or 
less perpend i cuIar to the blast (aspect B), and the 
remainder will be cases in which the web Is more 
nearly in line with the blast. 

The chart does not contemplate the destruction of 
the column by undermining of the footing. Such an 
action may cause destruction at a value of r/ w 1 ' 3 
of about 3. 

For charge weights lass than about 200 pounds, the 
rad I us of damage appears to be less than that given 
by the chart. 


The bulk of the incidents reported are for single 
story industrial buildings, with onlya few cases 
of doubtful validity of multi-story framed build¬ 
ings. All columns are single rolled steel sections. 

EXAMPLE: Given a building of average shed-type 
construction with l-columns 8 in. x $ in. u 35 
Ib/ft. of 12 ft. unsupported length and exposed to 
blast whose direction is 60° from the web, i.e. 
aspect 8. Then, A, • 10.3 sg. In., b' • 10 in., 
I * Uh In., so that A./b'l - 0.0073, the column 
Index under these conditions. It may be expected 
that such a coftimn will be blown out or severed 
by a 1000-1b GP AN-MUh boob at distances up to 
about 17 feet; the same bomb (aspect 8) will damage 
this column beyond repair at distancas up to about 
36 to U6 feet. 

When such detailed information on the construction 
Is not available, it is suggested that the column 
Index be taken as about 0.007, toward the upper 
part of the range for usual construction. 


mots : oar* rmcnamo mom unman u » pAwaac ncnomTS a wo oar* eomnitanoms 


November 1943 



K 


430 






















































































































WEAPON DATA 


BLAST DAMAGE TO CONCRETE COLUMNS 


(i A lb* 

CONCRETE 

COLUMNS 


DATA PREPARED FROM INFORMATION 6IVEN IN BRITISH RE 4 DAMAGE REPORTS AND DATA COMPILATIONS 



INDEX OF COLUMN 

SLENDERNESS AND 

ASPECT b'L 

0.20 


0.15 


0.05 


r DISTANCE FROM BOMB feet 
w'/3 CHARGE WEIGHT pounds 
2.0 


9^ Q 


500-lb 6 P AN - M 43 
CHS. WT. 266 1b 
1000-lb S.A.P. AN-M5' 

CHG.WT 308 1b. 

1000-lb G P AN-M44 
CHG.WT 538 1b. 

2000-lb. G P AN-M34 
CHG. WT 1077 lb. 

4000-lb. L .C AN - M 56 

chg w t. 3245 1 b. r DISTANCE FROM BOMB feet 

The curves define approximately the limiting distances from various bombs at 
will be damaged by blast in different ways - blown out or severed, damaged 
damaged critically. The width of the band is computed on 
the shape of a cross-section des i gned to carry a given load 


the ratio of the cross-sectional area of the 
the product of the length of the column and i 
joining the column to the bomb. The index is 
the column to its length, i.e. large values of 
to slender columns. 


which concrete columns 
beyond repair, or not 
the assumption of reasonable variations in 
The column index, plotted vertically, is 
column to the area exposed to the blast. This area is 
ts projected width on a line perpendicular to the line 
thus approximately equal to the ratio of the depth of 
the index correspond to stubby columns and small values 


0.10 


DEFINITIONS 

A - area of cross-section,s<7/>7ctes 
L - cleor height of column, inches 
b -horizontal dimension of column 
exposed to blast, inches 

r - distance from center of column 
to center of explosion, feet 
w - chorge weight of explosive, 

pounds 



r 


The columns are assumed to have no partitions or walls attached, and to be exposed to blast on all 
sides. If there are part i tions attached to the columns the radius of damage is likely to be greater, 
since part of the force on the attached elements is transmitted to the columns. Further, in such 
cases the blast wave cannot so readily make its way around the column to back it up from behind. On 
the other hand, where the column is supported by a wall or partition approximately in line with the 
blast wave, the radius of damage should be considerably smaller. 

The chart does not contemplate the destruction of the columns in the lowest story of a building by 
undermining of the footings. Such an action may cause destruction at a value of r/ w 1 ^ 3 of about 3. 
Neither does the chart consider the action of blast in a relatively confined space, which may cause 
tensile failure of the column by so-called "uplift" at a greater distance than shown by the chart. 

For charge weights less than about 200 pounds, the rad i us of damage appears to be less than that given 
by the chart. 

EXAMPLE: Given a building of average R/C frame construction having square columns with depth I /10 
the height. Then for blast perpendicular to the face of the column, the column index will be 0.10. 
It may be expected that such a column will be blown out or severed by a 1000-lb GP AN-M44 bomb at 
distances up to about 6 feet; the same bomb will damage the column beyond repair at distances up to 
about 16 to 22 feet. 

November 1943 



431 














































































WEAPON DATA 
DESTRUCTION OF 

CONCRETE FLOOR SLABS BY BOMBS 


0 


4.2 


£ 

CONCRETE 
FLOOR SLABS 


AREA REMOVED, 
thousands of square feet 



The chart indicates average areas of reinforced concrete floor slabs destroyed by bombs exploding 
within a building. The curves show, respectively, the average areas of destruction to be expected In 
the first, second and third floors above or below the bomb and the total area removed on all floors. 


It is to be noted that for maximum effectiveness, bombs of about 600 pounds charge weight or less re¬ 
quire at least two floors above and below the point of detonation and bombs of charge weight greater 
than 600 pounds require at least three floors above and below the point of detonation. Bombs of 
charge weight less than 200 pounds do not appear to produce significant damage. 

These curves apply only to ordinary reinforced concrete floor slabs, four to eight inches thick and 
supported on steel or concrete beams. Filler joist floors or other such types are not included. 

In using the chart it should be remembered that the amount of available data on which this presenta¬ 
tion is based is small, and some individual values differ from the average represented by the curve 
by as much as 100£. 

SOURCE: Data Compilations and Incident Summaries of the British Ministry of Home Security. 


August 1944 


432 



























































































WEAPON DATA 

REMOVAL OF 

LIGHT-WEIGHT SHEET ROOFING BY BLAST 



A MAXIMUM RADIUS OF REMOVAL AS A FUNCTION OF THE CHARGE WEIGHT 



THESE CURVES GIVE APPROXIMATE MAXIMUM DISTANCES, MEASURED ON PLAN, AT WHICH THE REMOVAL OF 
SHEET ROOFING MAY BE EXPECTED DUE TO EXPLOSION OF VARIOUS CHARGES INSIDE OR OUTSIDE OF STEEL- 
FRAME FACTORY TYPE BUILDINGS. GERMAN MINES APPARENTLY PRODUCE GREATER BLAST EFFECTS 
THAN BOMBS OF EQUAL CHARGE WEIGHT. ACCORDINGLY , CHARGE WEIGHTS FOR "C"AND "D"TYPEFARA- 
MINES SHOULD BE TAKEN ABOUT 60% GREATER THAN THEIR NOMINAL VALUES , WHILE THAT FOR THE 
TYPE V MINE SHOULD BE INCREASED ABOUT 40% IN ORDER TO ALLOW FOR THE EFFECTOFARELA: 
TIVELY THICKER STEEL CASE. 

]) REMOVAL OF ROOFING BY ONE 11 0-lb. (50kg.SC)G.P. BOMB EXPLODING INSIDE SINGLE STORY SHED-TYPE 
BUILDINGS OF VARIOUS VOLUMES 



THIS CHART GIVES THE AVERAGE EQUI¬ 
VALENT RADIUS OF REMOVAL OF SHEET 
ROOFING BY A SINGLE IIO-lb.G.P. (50 kg., 
sc)BOMB EXPLODING INSIDE OF SINGLE 
STORY SHED BUILDINGS OF VARIOUS 

VOLUMES.AVERAGE RADIUS IS THE 

RADIUS OF A CIRCLE OF AREA EQUAL 
TO THE AREA OF DAMAGE,ALL MEASURE¬ 
MENTS BEING ON PLAN ....THE AVERAGE 
HEIGHT OF BUILDINGS EXAMINED IS 20 ft. 
TO EAVES. ASBESTOS CEMENT ROOFING 
IS AFFECTED TO A MUCH GREATER DIS¬ 
TANCE THAN CORRUGATED IRON; HOW¬ 
EVER ,THE LATTER HAS A GREATERTEN- 
DENCY TO CONFINE THE EXPLOSION. 


WHEN HOOK BOLTS ARE PLACED MORE THAN ONE TO EACH 6 TO 8 SQUARE FEET OF CORRUGATED IRON ROOFING, PURLINS WILL BE 

DAMAGED ;WITH FEWER HOOK BOLTS, A RELATIVELY GREATER NUMBER OF SHEETS WILL BE BLOWN OFF.INSULATION BOARD 

PLACED UNDER THE PURLINS PROMOTES TRANSFER OF BLAST UPLIFT EFFECT TO THEM , USUALLY CAUSING GREATER STRUC¬ 
TURAL DAMAGE.... RADII OF DAMAGE FOR BOARDED ROOFS CAN BE TAKEN TO BE APPROXIMATELY 30% LESS THAN THOSE 

FOR STEEL SHEETS.FOR SLATES AND TILES ON BATTENS, RADII ARE OF THE SAME ORDER AS THOSE FOR ASBESTOS 

CEMENT.CHARTS "A" AND "B" ARE BASED ONLY ON INCIDENTS IN WHICH BOMBS E XPLODED AT OR ABOVE GROUND 

LEVEL. DAMAGE WOULD BE EXPECTED TO BE LESS FOR EXPLOSIONS BELOW GROUND. 


DATA COMPILED FROM R.E. NOTE 220 AND R.E 4- DATA COMPILATION NO 8, BRITISH MINISTRY OF HOME SECURITY. 

September 1943 


433 


















































































































































































WEAPON DATA 

EFFECT OF EARTH SHOCK ON 
UNDERGROUND REINFORCED CONCRETE WALLS 



UNDERGROUND R/C WALLS 


MAXIMUM DISTANCE for indicated degree of damage^r in ft 


WALL 

THICKNESS, ft 1 

100-lb GP AN-M30 

250-lb GP AN-M57 
500-lb SAP AN-M58 

500-lb GP AN-M64 

1000-1 b SAP AN-M59 

1000 -lb GP AN-M65 

2000-lb GP AN-M 66 

12000-lb GP TI0 

22000 -lb GP TI4 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

MODERATE 

HEAVY 

BREACH 

1 

11 .6 

7.8 

5.6 



















2 

8.2 

5.8 

4.2 

12.4 

8.7 

6.3 

18.0 

12.4 

9.0 


17.0 

12.3 










3 

6.5 

4.6 

2.9 

10.1 

7.1 

5.0 

14.7 

10.5 

7.5 

21.0 

14.6 

10.6 

29.8 

20.2 

14.7 







4 

5.3 

3.5 


8.5 

6.0 

3.7 

12.7 

9.0 

6.3 

18.2 

12.9 

9.2 

25.9 

18.1 

13.1 


36.0 

26.0 




5 

4.3 

1.8 


7.2 

4.9 


II .1 

7.8 

4.9 

16.2 

1 1 .5 

8.1 

23.0 

16.4 

1 1.8 

49.0 

33.5 

24.0 


36.0 

26.0 

6 

2.5 



6.3 

3-8 


9.8 

6.6 

2.5 

14.6 

10.3 

6.8 

21 .0 

14.9 

10.5 

46.5 

32.0 

23.0 

50.0 

33.5 

24.5 

7 




5- * 



8.6 

5.7 


13.2 

9.1 

5.2 

19.3 

13.7 

9 .4 

41.5 

29.0 

21.5 

46.0 

32.0 

23.0 

8 




2 . g 



7.6 

4 • 2 


11.9 

8.1 


17.8 

12.5 

7.9 

39.0 

27.5 

20.0 

43.5 

30.5 

21.5 

9 







6.6 



10.9 

7.1 


16.3 

1 1.3 

6.1 

36.5 

26.0 

18.5 

40.5 

28.5 

20.5 

10 







4- 7 



9.9 

5. 6 


15.2 

10.4 


34.5 

24.5 

17.5 

38.5 

27.5 

19.5 


The bombing efficacy is nr*/w where rcr 2 is the area in square feet within which any walls present will be damaged, 
and w is the weight of the explosive charge in the bomb, in pounds. For area bombing of underground walls, the ef¬ 
ficacy reaches a maximum for t/u>V 3 between 0.4 and 0.5, where t is the thickness of the wall in feet. This deter¬ 
mines the optimum size of bomb for area bombing of underground walls of any known thickness. 

Similarly, for area bombing of very long narrow underground targets with reinforced concrete walls, the maximum ex¬ 
pectation of damage per pound of explosive will be attained for t/u^ a between 0.8 and 1.0 for breaching or heavy dam¬ 
age . 


DAMAGE CRITERIA ASSUMED: 


DESCRIPTION 
OF DAMAGE 

TYPE OF DAMAGE 

d/L, 
in/ft 

2 -edge support 

4-edge Support 

SLIGHT 

Fine Cracks 

Fine Cracks 

0.02 

MODERATE 

Medium Cracks 

Light Scabbing 

0.1 

HEAVY 

Heavy Cracks 
and Scabbing 

Severe 

Scabbing 

0.2 

BREACHING 

Breached 

Breached 

0.5 



The table gives values of the maximum d istance at which 
various degrees of damage will result from detonation 
of bombs in earth. The figures given in the table 
apply to lightly reinforced rectangular concrete wal 1 
panels supported along either two opposite edges or 
along all four edges. The bomb is assumed to be ap¬ 
proximately opposite the center of the face of the 
wal 1 ; any marked departure from this position will gen¬ 
erally result in less damage. Under the same condi¬ 
tions the 2 -edge and 4-edge supported walls will be 
damaged differently as described by the Damage Crite¬ 
ria above, but the ratio of central deflection to span 
is a good measure of damage for both types. 

This information is based on tests of walIs whose face 
dimensions are in the ratio of about 3:5, and whose 
span to thickness ratio is between 5:I and 15:I. The 
test walls were reinforced with mild steel bars, about 
one percent by volume. Damage and central deflection 
were measured for bombs detonated at various distances 
on the earth side of the wall as shown in the sketch. 
Charge weights used in these tests ranged from 1/8 lb 
to 1000 lb. 

The graph gives the ratio of central deflection to span 
for various wall thicknesses and charge distances in 
terms of the scale variables t/w 1 ' 3 and r/w 1 ' 3 . 

Tabulated values based on only meager data are given 
in italics. Similarly, the corresponding parts of 
the curves on the graph are dotted. 



SOURCES: 

Tests by Ministry of Home Security and Road Research Laboratory (British) and by Committee on Fort ification Design (U.S.A.) 


Ref: EWT-5g (0SRD-5405g) 
^Revised: August 1945 





































































































































WEAPON DATA 

DAMAGE TO REINFORCED CONCRETE 
WALL PANELS BY DETONATIONS IN AIR 


(> A<r 

^ W DAMAGE TO 

R/C WALLS IN AIR 


MAXIMUM DISTANCE for indicated degree of damage,r in ft 

WALL 

THICKNESS, ft 

100-1 b GP AN-M30 

250-lb GP AN-M57 
500-lb SAP AN-M58 

500-lb GP AN-M64 
1000-lb SAP AN-M59 

1000-lb GP AN-M65 

2000 -lb GP AN-M66 

12000 -lb GP TI0 

22000-lb GP TI4 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

BREACHING 

MODERATE 

HEAVY 

i__ 

BREACHING 

1 

1 

3.1 

-2.2 

1 .2 

5.4 

4.4 

2.6 

9.4 

7.9 

3.9 



9.0 










2 

1 .2 

0.5 


2.4 

1.3 

0.5 

4.2 

2.8 

1.4 

7.2 

5.4 

CO 

• 

o 

11.8 

9.6 

5.7 



18.9 




3 

0.5 



1.3 

0.3 


?.5 

1.2 

0.1 

4.4 

2.6 

1 .2 

7.4 

5.0 

2.6 

23.7 

20.0 

12.4 

35.0 


18.6 

4 




0.7 



1,6 

0.3 


3.0 

1 .3 


5.2 

2.9 

l.l 

15.8 

12.0 

16.7 

24.2 

19.6 

1 1 .8 

5 







1 0 



2.1 

0.4 


3.8 

1.7 


12.2 

8.3 

4.3 

19.6 

14.9 

8.3 

6 










1 .4 



2.8 

0.7 


10.3 

6.5 

3.1 

15.7 

1 1 .0 

5.7 

7 













2.1 

0.1 


7.9 

4.1 

1 .2 

12.8 

8.1 

3.8 

8 













1.5 



6.7 

3.1 

0.3 

10.7 

6.2 

2.4 

9 
















5.5 

2.1 


9.4 

5.0 

1 .5 

10 
















4.6 

1 .2 


8.1 

3.6 

0.2 


The bombing efficacy is where nr 2 is the area in square feet w ithin wh ich any wal 1 s present wi 11 be damaged, and w 
is the weight of explosive charge in the bomb, in pounds. For area bombing of reinforced concrete walls the efficacy 
increases with the charge weight, so the maximum damage per pound of explosive will be attained by use of the bomb with 
the largest possible charge. 

Similar reasoning shows that for area bombing of very long narrow targets having reinforced concrete walls, the bomb 
with the largest possible charge gives the greatest expectation of damage per pound of explosive. 


DAMAGE CRITERIA ADOPTED: 


DESCRIPTION 
OF DAMAGE 

TYPE OF DAMAGE 

Deflec’n 
Aver - Span 
ml ft. 

SLIGHT 

Slight Cracking and Bending 

0 . 1 

MODERATE 

Light Punching and Cracking with 
Possibly Some Spalling 

0.5 

HEAVY 

Heavy Punching, Shattering, or 
Possible Perforation 

1.2 

BREACHING 

Perforation with Extensive Scab- 
ing. Bars May be Bent or Bulged. 

— 


The table gives max. distance at which an air-backed reinforced 
concrete wall or wall panel that will experience various 
degrees of damage due to explosion of TNT-filled bombs in 
air nearby or in side-on contact with the wall. 

These data derive from tests,both model and full scale,on 
rectangular panels with face d imens ions from 3 to 25 times 
the thickness. Charges used in tests ranged from about It 
oz. to 1700 lb. Test panels were supported along all four 
edges,and results showed no appreciable difference between 
freely supported and fixed edges. 

Tests involved various degrees of reinforcing and differ¬ 
ent explosives, but all data were reduced to a basis of 
steel by volume and bombs filled TNT.Degree of damage and 
ratio of central deflection to span correlate fairly well 
for si ight, moderate and heavy damage. 

Tabulated data refer to about ^ reinforcing steel by vol¬ 
ume. For steel, multiply thickness values by 0.9 for 
breaching and by 0.7 for other degrees of damage. 

Fragments from nearby bomb detonations usually cause sur¬ 
face scars and a few perforations; this type of damage is 
not included in the present analysis. 

The graph gives damage curves in terms of scale variables 
r/w 1/2 and t/w 1/a , where t*wall thickness (ft), r -distance 
from wall to bomb (ft) and w -weight of charge (lb). 



For contact and very near contact shots, nose-on position 
of a bomb will cause less damage than side-on.Figures given 
correspond to side-on position,the bomb detonating not far 
from a point opposite center of wal1.Positions appreciably 
offside usually result in lessened damage. 

t/w v », /t/J6 v » 



SOURCE: Tests by Ministry of Home Security (British), Ordnance Department (U.S.A.), and Corps of Engineers, (U.S.A.). 


PTM No.104 & EWT-3 
* Revised: August 1945 



435 




















































































































WEAPON DATA 

DAMAGE TO SINGLE-STORY 
INDUSTRIAL BUILDINGS BY HE BOMBS 


(i 1 


il 


HE EOMBS: 
INDUSTRIAL BUILDINGS 


A. STRUCTURAL DAMAGE DUE TO HIGH EXPLOSIVE BOMBS 

The table gives the Mean Area of Effectiveness (MAE) and the near miss distance for common General Purpose bombs (fuzed 
0.1 seconds delay nose, 0.01 seconds delaytaiI ) on European Type industrial bui1dings, and for the 4000-lb LC bomb (fuzed 
instantaneous). Bombs striking within the near miss distance from the building may be expected to cause damage compara¬ 
ble to that of a direct hit in about one out of ten cases. Bombs striking further from the building than the near miss 
distance cause no appreciable structural damage. The effects of the near miss hits are included in the values of MAE 
tabulated below. 



STRUCTURAL CLASS 

MA 

:, sq feet 

per bomb, and NEAR MISS DISTANCE, r in feet 



1 , and Jj 

500- 

-lb GP 

1000-lb GP 

2000-lb GP 

4000- 

lb LC 


MAE 

NEAR MISS 
DISTANCE 

MAE 

NEAR MISS 
DISTANCE 

MAE 

NEAR MISS 
DISTANCE 

MAE 

NEAR MISS 

D1 STANCE 

(1 

Single story, areas > 1 0p00 
sq.ft. Principal spans of 
roof trusses <75 ft. Height 
\ to eaves generally <25 ft. 

,} Roof structure: simple beams 
S and columns, archesor rigid 
frames, trusses, sawtooth 
trusses, etc. No traveling 
cranes. 

3050 
± 250 

15 ft 

6400 

20 ft 

12,800 

35 ft 

32P00 

80 ft 

c * 

Single story, areas > 10,000 
so ft. Principal spans of 
roof trusses>75 f t. Height 
to eaves generally>25 ft. 
Roof structure:lattice trus¬ 
ses. long span arches,etc. 

No traveling cranes. 

5270 
+ 9 50 

15 ft 

1 1,000 

20 ft 

22,000 

35 ft 

55,000 

80 ft 

(l 

A11 single story buildings 
)lof<l0,000 sq.ft, planearea 

3100 
+ 250 

15 ft 

6500 

20 ft 

1 3p00 

35 ft 

33pOO 

80 ft 


Results for the 500-lb GP bomb were obtained from an analysis of 38 USAAF attacks on European Industrial targets. The 
values of the MAE's were determined from the damaged data, and from the number of hits as determined by photointerpreta¬ 
tion, The MAE's were determined from the relation g = A [1-(1-M/A) where g is the total area of damage, in square feet, 
A is the total area of the building in square feet, h is the total number of hits, and M is the MAE per bomb. Bombs used 
in the raids analyzed were fuzed 0.1 nose and 0.01 tail, or 0.1 nose and 0.025 tail, the majority of the bombs having 
the shorter fuzing. See EWT-2f for averaging process for a number of damaged buildings. 

Values given for the 1000-lb and 2000-lb bombs were estimated from the values determined for the 500-lb GP bomb on the 
assumption that the MAE is proportional to the weight of charge in the bomb. Experience has shown that this assump¬ 
tion is approximately correct. 

B. STRUCTURAL AND FIRE DAMAGE DUE TO HIGH EXPLOSIVE BOMBS 

Analysis of a number of incidents has shown that the probability ot a serious fire being started by a 500-lb GP bomb is 
0.17. Thus the overall mean area of effectiveness for structural and fire damage in industrial buildings with 500-lb GP 
bombs is 0.83(MAE) + 0.17(E) where MAE is the mean area of effectiveness for structural danaqe and E is the average 
expected damage due to one fire. For combustible buildings, E is the total area of one fire division; for non-combus¬ 
tible byildings, E is approximately 35,000 sq.ft, for large fire divisions and a correspondingly smaller area for fire 
divisions smaller than 100,000 sq.ft, (see graph on sheet 6 82). The table gives the gross MAE for both structural dam¬ 
age and fire damage for European industrial type buildings attacked by 500-lb GP bombs fuzed 0.1, nose, and 0.01, tail. 


STRUCTURAL 
CLASS 
see above 

COMBUSTIBLE 

or 

NON-COMBUSTIBLE 

GROSS MAE.sg ft per bomb for Structural and Fire Damage by 500-lb GP Bombs 
on Fire Divisions of Different Areas, sq ft 

7,000 

15,000 

30,000 

60,000 

100,000 

200,000 

I 

C 

3720 

5080 

7630 

12,730 

19,500 

36,500 

1 

N 

3650 

4570 

6130 

7390 

8100 

8370 

TL 

C 

5560 

6920 

9470 

14,570 

21,400 

38,400 


N 

5490 

6410 

7970 

9230 

9940 

IQ2I0 

U 

C 

3760 

5120 

7670 

12770 

19,600 

36J600 

O 

N 

3690 

4610 

6170 

7430 

8140 

8410 


DEFINITIONS: 

FIRE DIVISION: An area of a building separated from other areas by fire walls or by air gaps, within which a fire is 
expected to be retained. 


COMBUSTIBLE: A building with roof which is constructed of wood sheathing or planking irrespective of whether or not it 

Is supported by wood or non-combustible framing. Tile roofs on wood sheathing are also included in this classification. 

NON-COMBUSTIBLE: A building with roof which is constructed of non-combustible material such as gypsum slab, concrete 
slab, corrugated iron, etc, and supported on exposed steel framing. 

Once a fire is sufficiently well established to produce "serious" damage the extent of its spread does not depend on 
whether the fire is initiated by an Incendiary Bomb or by a High Explosive Bomb. • 

A fire well established in a combustible roof single story fire division will usually burn out the division completely. 

The structural classes given in the table are not characteristic of European construction only. Construction practice 
in various countries shows enough similarity to warrant using the values given for structural damage universally. Dif¬ 
ferences in roofing material may change the gross MAE materially. 


Ref: £WT-2f, 3b, 3c 
August 1945 

















































WEAPON DATA 

DAMAGE TO SINGLE-STORY 

INDUSTRIAL BUILDINGS BY INCENDIARY BOMBS 


() 




NCENOIARIES: 
INDUSTRIAL BUILDINGS 


Damage to industrial buildings by Incendiary Bombs is due to fires started by the bombs. The probability of an Incen¬ 
diary Bomb starting a fire in a building depends strongly upon 

ROOF - Whether combustible or non-combustible. 

HEIGHT - He i ght to eaves of a single story building. (Height of upper story only for multi-story buildings) 

OCCUPANCY - Percentage of floor area covered by combustible material, as estimated by Intelligence. 

Once a fire is sufficiently well established to cause " serions" damage the extent of its spread does not depend on the 
origin of the fire. A fire well established in a combustible roof fire division will usually burn out the entire fire 
division. A fire well established in a non-combustible roof fire division usually burns out only a part of the fire 
division. 

The Mean Area of Effectiveness, MAE, of incendiary bombs for one fire division of an industrial building with a combus¬ 
tible roof is equal to the area of the fire division times the probability of afire being started by an incendiary bomb; 
for an industrial building with a non-combustible roof, the MAE is equal to the area which will be burned out*time$ the 
probability of a fire being started by an incendiary bomb. Thus the MAE depends on the roof, the height, the occupancy 
and the area of the fire division. The table gives the MAE in square feet per bomb for various combinations of these 
factors *(See graph below) 

MEAN AREA OF EFFECTIVENESS, (MAE) square feet per bomb, FOR INCENDIARY BOMBS AGAINST INDUSTRIAL BUILDINGS 


100-lb, IB, AN-M47 

Area of One Fire Division, sq ft 

Area 

4-lb, IB, AN-M50 
of One Fire Division, sq 

ft 

7000 

15000 

30000 

60000 

100000 

200000 

7000 

15000 

30000 

60000 

100000 

200000 

2300 

5000 

9900 

19800 

33000 

66000 

0 

0 

0 

0 

0 

0 

4600 

9900 

19800 

39600 

66000 

132000 

140 

300 

600 

1200 

2000 

4000 

5500 

1 1700 

23400 

46800 

78000 

156000 

350 

750 

1500 

3000 

5000 

10000 

6200 

13400 

26700 

53400 

89000 

178000 

700 

1500 

3000 

6000 

10000 

20000 

7000 

15000 

30000 

60000 

100000 

200000 

1050 

1250 

4500 

9000 

15000 

30000 

1200 

2500 

5100 

10200 

17000 

34000 

0 

0 

0 

0 

0 

0 

2400 

5000 

9900 

19000 

33000 

66000 

70 

150 

300 

600 

1000 

2000 

2700 

5800 

1 1700 

23400 

39000 

78000 

210 

450 

900 

1800 

3000 

6000 

3100 

6600 

13200 

26400 

44000 

88000 

350 

750 

1500 

3000 

5000 

10000 

3500 

7500 

15000 

30000 

50000 

100000 

490 

1050 

2100 

4200 

7000 

14000 

490 

1050 

2100 

4200 

7000 

14000 

0 

0 

0 

0 

0 

0 

840 

1800 

3600 

7200 

12000 

24000 

0 

0 

0 

0 

0 

0 

1 120 

2400 

4800 

9600 

16000 

32000 

140 

300 

600 

1200 

2000 

4000 

1260 

2700 

5400 

10800 

18000 

36000 

210 

450 

900 

1800 

3000 

6000 

1400 

3000 

6000 

12000 

20000 

40000 

280 

600 

1200 

2400 

4000 

8000 1 

210 

450 

900 

1800 

3000 

6000 

- 

- 

- 

- 

- 

- 

490 

1050 

2100 

4200 

7000 

14000 

- 

- 

- 

- 

- 

- 

560 

1200 

2400 

4800 

8000 

16000 

- 

- 

- 

- 

- 

- 

630 

1350 

2 700 

5400 

9000 

18000 

- 

- 

- 

- 

- 

- 

700 

1500 

3000 

6000 

10000 

20000 

- 

- 

- 

- 

- 

- 

0 

0 

0 

380 

820 

0 

0 

0 

730 

1600 

0 

0 

0 

1200 

2600 

0 

0 

0 

1700 

3700 

0 

0 

0 

2000 

4300 

0 

0 

0 

2100 

4500 






■ 


BUILDING CLASSIFICATION 


Height 
feet 


Occupancy 

percent 


7-9 

or 

10- 19 


5 

15 

25 

35 

45 


20-29 


5 

15 

25 

35 

45 


30-39 


5 

15 

25 

35 

45 


40-49 


5 

15 

25 

35 

45 


50-59 


0-45 


all heights 


5 

15 

25 

35 


DEFINITIONS: 

FIRE DIVISION: An area of a building separated from 

other areas by fire walls or by air gaps, within which 
a fire is expected to be retained. 

COMBUSTIBLE: A building with roof which is constructed 

of wood sheathing or planking irrespective of whetheror 
not it is supported by wood or non-combustible framing. 
Tile roofs on wood sheathing are also included in this 
classification. 

NON-COMBUSTIBLE: A building with roof which isconstruct- 

ed of non-combustible material such as gypsum slab, con¬ 
crete slab, corrugated iron, etc., and supported on ex¬ 
posed steel framing. 


Values given for the M-q 7 are considered more reliable 
than those for the M-50. 

The information given here was based on 



me 1 inurmdilun given nere was Dasefl on analysis ot uoaat aiiacKs on turopean industrial targets. inese value: 
can be applied to structures of other types only if the effects of differences in construction, combustibility of the 
roof, and type and extent of the occupancy are taken into account. (See EWT-5) 


Ref: EWT-5b, 5c, 5d 
August 1945 


437 


























































































WEAPON DATA 


BOMBING OF STEEL MILLS 



In a steel plant large enough for coke ovens and steel furnaces to be used as sep¬ 
arate targets, the best bombs are the 500-1b GP fuzed 0.025 sec delay for the coke 
ovens and the 2000-lb GP fuzed 0.025 or 0.1 sec delay for the steel furnaces. If 
one overall attack is to be made, the best bomb is the 1000-lb GP fuzed 0.025 sec 
delay, with the 2000-lb GP fuzed 0.025 sec delay a good second choice. 


The principal components of a steel mill inorder of their vulnerability to bomb¬ 
ing attack, the recommended bomb and fuze delay, and the results to be expected 
from bombing attack are as follows: 


COMPONENT 

RECOMMENDED 

BOMB & FUZE 

RESULTS 

Coke Ovens 

500-lb GP or 
1000-lb GP. 
0.025 sec 
del ay 

One direct hit will disable one section for 3 
to 8 months. This will reduce the quantity of 
coke and gas available to the blast furnaces. 
Auxilliary equipment such as the aspirating 
pi ant, coke 1 oad i ng and ramming equ i pment, etc. 
is also highly vulnerable. 

Open Hearth 
Furnaces 

2000-lb GP or 
1000-lb GP. 
0.025 or 0.1 
sec delay 

At least 25% of the furnaces must be damaged 
to affect production seriously. Damaged ovens 
require several months for repairs. Gantry 
cranes and other equipment are additional tar¬ 
gets. 

Blooming Mills 

2000-lb GP or 

1000-1b GP. 
0.025 or 0.1 
sec delay 

These are frequent 1y a bott1eneck of the plant. 
Small,target, but essential to operation and 
difficult to repair. Smaller bombs could dam¬ 
age controls. 

Blast Furnaces 
and related 
equipment 

2000-lb GP 
0.025 or 0.1 
sec delay 

Direct hits required. Small target. Stoves, 
hoists, and charging equipment are also vul¬ 
nerable to smaller bombs. Long repair or re¬ 
building time if a direct hit is made on fur¬ 
nace 

Conveying 

Equipment 
and 

Services 

500-lb GP 
or larger 

Good secondary objectives within the target 
area. Bridge cranes at ore docks, coke push¬ 
ers, gantry cranes throughout plant, etc. are 
all essential and vulnerable to direct hits. 
Services are essential and vulnerable to direct 
hits or near misses. 

Air 

Compressors 

2000-lb GP 
or larger. 

0.1 or 0.025 
sec delay 

Important, but of very heavy construction. 
Small target difficult to hit and damage. 


438 


Ref: EWT-6d 
August 1945 























WEAPON DATA 

BOMBING OF DAMS 



Planning attacks on dams of all types requires careful engineering investigation 
of the design. In general, the largest practicable bomb should be used. Many dams 
will not be vulnerable to any bomb smaller than the 12,000-lb or 22,000-lb GP, or 
some special weapon. 

Attack on a dam should be made when the water level behind the dam is at its high¬ 
est stage. 

Earth dams are best attacked with GP bombs: by deeply cratering the crest if the 
dam contains no steel or concrete core; by deep penetration and resulting shatter¬ 
ing of such a core if present; or by deeply cratering the upstream slope of the 
seal blanket. The choice of the method depends on the design. Long delay fuzing 
should be used in most cases. 

Masonry and concrete dams should be attacked by the underwater explos ion of a large 
charge in contact with the dam on the upstream side; the details to be carefully 
worked out for all larger dams. Fuzing should be of short del ay, suffic ient to de¬ 
velop the full tamping effect of the water. 

Gates can be attacked by the adjacent underwater explosion on the upstream side 
of fairly large bombs with short delay fuzing (0.025sec) sufficient to develop 
the full tamping effect of the water. 

Operating machinery and control houses are best attacked by the direct hit of in¬ 
termediate sized bombs fuzed wi th slight delay (0.025 sec or 0.01 sec) for penetra¬ 
tion into the building. There is no appreciable near-miss damage and even total 
destruction is not too serious. 


Ref: FVT-5 
August 1945 



WEAPON DATA 


BOMBING OF PENSTOCKS 



The best mode of attack on penstocks is by means of bombs that will penetrate the 
pipe and explode in the interior. The use of bombs intended to produce large move¬ 
ments of the pipe through earth shock, a i r blast, or by cratering, is not like¬ 
ly to be effective. 

It is recommended that GP bombs, fuzed 0.01 sec nose and tail, be used. Table I 
shows sizes of bombs required to rupture penstocks when the bomb explodes at the 
center of the penstock. Generally, an up-slope approach within 30° of the pipe 
axis, at medium to high altitude gives the largest equivalent horizontal vulnera¬ 
ble area. But the probability of hitting the pipe and of the explosion occurring 
in the lethal annulus of the pipe must be considered. 


Table I 

SIZES OF BOMBS REQUIRED TO RUPTURE PENSTOCKS WHEN EXPLODED kl THE CENTER 


Diameter of 

P i pe 

ft 

Thickness of 

P i peW al 1 

t 77 

Size of Rupturing 

C harge of TNT 

lb 

Size of GP Bomb 

lb 

22 

1 .50 

525 

1000 

16 

1 .25 

240 

500 

13 

1 .00 

127 

250 

10 

0.75 

56 

100 


If the bomb explodes near the side wall, a smaller bomb than listed above may be 
sufficient to split the pipe. 


A detailed study of the vulnerabi1ity of penstocks i s g i ven i n the first reference. 
On the basis of model tests made to determi ne the weight of charge required to rup¬ 
ture a penstock by internal explosion, and of ricochet tests conducted against curv¬ 
ed air-backed plates and against water-filled cylinders, recommendations are made 
as to the weapon to be used in attack. A table of equivalent horizontal vulnerable 
area factors is g iven f orvarious slopes of penstocks, angles of fall of bomb, and 
angles of attack, as an a i d to selecting the best combination of bombing conditions 
and the lowest required bomb density. A procedure for analyzing a penstock instal¬ 
lation to determine the type of bombing attack required is given. By means of this 
analysis, the type, s ize, and fuzing of bombs and the bombing density can be deter¬ 
mined for any desired probability of destruction of the penstock. Diagrams and 
curves are given to assist in the computation. 


Ref: EWT-2b 
August 1945 


















WEAPON DATA 


BOMBING OF GUN POSITIONS 

OPEN GUN EMPLACEMENTS 

The table gives the Mean Area of Effectiveness for unserviceability and the Mean Area of Effectiveness for temporary un¬ 
serviceability in square feet per bomb for light, medium, and heavy guns. Values are for guns that do not have protec¬ 
tive shielding of the vulnerable parts. 

In the table, guns are classified as light (20mm and 37mm), medium (75mm to 120mm) and heavy (150mm and larger). Unser- 
viceability means damage requiring shop repair or more than 24 hours field repair. Temporary unserviceability means un¬ 
serviceable but repairable in less than 24 hours. MAE is defined in data sheet 6 D3. 



MEAN AREA OF EFFECTIVENESS PER BOMB FOR VARIOUS BOMBS vs UNSHIELDED GUNS 


"TD 

<D 

-4-> 

BOMB 


Light 

Guns 

Medium and Heavy Guns 

Crater 
Radi u s 
feet 

Fuzing 

sec 

MAE for Unservice¬ 
ability 

sq.ft. 

MAE for Temporary 
Unserviceabi1ity 

sq. ft. 

MAE for Unservice¬ 
ability 

s q. ft. 

MAE for Temporary 
Unserviceabi1ity 
sq. ft. 

11 

100-1b GP,AN-M30 

9.25 

1/100 

1000 

4300 

270 

1600 


250-lb GP,AN-M57 

12.0 

or 

1800 

7200 

450 

2700 

F— c 
cn a) 

500-lb GP,AN-M64 

15.5 

1/40 

3000 

12000 

750 

4500 


1 000-1b GP,AN-M65 

19.75 

it 

4900 

19600 

1200 

7300 

Z 

O c 

20 -lb F,AN-M41 


Inst. 



300 

600 

H* Cl 

20-lb Para.Frag 


n 



300 

600 


90-lb F,AN-M82 


n 

Lack of data does not warrant 

2400 

4800 

UJ— 

100-1b GP,AN-M30 


it 

prediction of MAEf or lightguns. 

3700 

7400 

O <n 

260-lb F,AN-M81 


ii 



7000 

14000 

CXL 3 
U_ CT 

500-lb GP,AN-M64 





10400 

20800 

— 


MEAN AREA OF EFFECTIVENESS for UNSERVICEABILITY 


—-- - - n 

BOMB 

Fuzing 

Light Guns 

Diameter of Emplacement 


)iameter 

Medium Guns 
of Emplacement 

-—.r-. - -r.. 

20' 

30' 

40' 

50' 

60' 

20' 

30' 

40' 

50' 

60' 

y*-' 

20-1b F,AN-M41 

Inst. 

300 

- 

- 

- 

- 

300 

- 

- 

- 

- 

o £ 

20-lb Para.Frag 

n 

300 

- 

- 

- 

- 

300 

- 

- 

- 

- 


90-lb F , AN-M82 

it 

600 

1100 

1800 

2600 

3600 

600 

950 

1500 

2000 

2300 

£ > 

100- 1 b GP , AN-M30 

it 

600 

MOO 

1800 

2600 

3600 

600 

1100 

1800 

2400 

3200 

UJ 
y r 

260-lb F.AN-M8I 

n 

600 

1 100 

1800 

2600 

3600 

600 

1 100 

1800 

2600 

3200 

o— 

500-lb GP , AN-M64 

ii 

600 

1 100 

1800 

2600 

3600 

600 

MOO 

1800 

2600 

3200 


n 

VT 

10400 

10400 

10400 

10400 

10400 

10400 

10400 

10400 

10400 

10400 


n 

n 

20800 sq.ft. MAE 

for Temporary Unserviceability 

for all 

revetted guns. 



COVERED CONCRETE GUN EMPLACEMENTS 

Covered concrete gun emplacements can be destroyed by a bomb perforating the roof and detonat ing inside of the structure, 
or seriously damaged by a bomb exploding underground close to the side walls. Bombs should be fuzed 0.025 seconds delay 
for either type of damage. Data sheet 2CI a may be used to select bombs capable of perforating the roof, and the radii 
for breaching given in Data Sheet 6A5* may be used as near miss distances for damage underground explosion close to the 
wall. The vulnerable area for perforation is the inside plan area of the gun emplacement, and the vulnerable area for 
damage by near misses is the area of a band around the outside of the emplacement, having a width equal to the near miss 
distance defined above. The most efficient bomb is that bomb having the largest vulnerable area per ton, and is usually 
the smallest bomb capable of perforating the roof of the gun emplacement. 


Ref: EWT-6a 
August 1945 





















































WEAPON DATA 

DAMAGE TO UNDERGROUND PIPING 


(> 15 1 

^ w UTILITIES: 

UNDERGROUND PIPING 


RADIUS OF DAMAGE R, feet 



The curves show average radius of damage by medium-sized bombs to pipes made of (a) cast iron and (b) earthenware, brick 
or tile buried in clay soil. The radius of damage R thus represents roughly the half width of a band within which the 
pipe will be vulnerable. 

SOURCE OF DAMAGE: Damage appears to be caused largely by earth movement rather than by forces transmitted longitudinally 
through the pipe or through its contents. Services laid in ducts are protected by the "trench effect"; the ducts may be 
damaged but ground shock will be absorbed, permitting the services to remain intact. 

LENGTH OF CAST IRON PIPE DAMAGED: The length of pipe requiring replacement is of the order of one and one-half to two 
times the radius of damage. 

NATURE OF DAMAGE TO CERAMIC PIPE: Earthenware, brick and tile services can be placed in a single category because fail¬ 
ure almost always occurs at the joints, which are of comparable strength in all three. 

EFFECT OF DEPTH: Data used in compiling results is for services buried at depths of from 2i to 5 feet, over which range 
no depth effect is found. Farther, the radius of damage depends very little on the depth of the explosion, within the 
normal limits of bomb penetration. 

SIZE OF PIPE: There is no apparent dependence of radius of damage on pipe size within the range commonly used. 

MAINTENANCE OF PRESSURE IN WATER SERVICES: In the event that damage to the pipe or its fittings does not result in a 
complete break, the pressure may hold at a substantial fraction of its normal value for some time. The drop in pressure 
immediately following the explosion is generally found to i ncrease with W 'V r, where r i s the di stance from the charge. 

OTHER SOILS: Compared with clay, the radius of damage is to be taken slightly smaller in chalk, sand and gravel and 
slightly more in made ground. If the soil is saturated with water, damage will usually extend to greater distances.* 

Source of data! Reports of the British Ministry of Home Security and experiments conducted for the Corps of Engineers, 
U. S. Army, at Aberdeen Proving Grounds. 


see sAeef 3 

January 1943 


444 




















































































WEAPON DATA 

BOMBING OF AIRFIELD RUNWAYS 



AIRFIELD RUNWAYS 


The best method for damaging runways and landing grounds is by cratering with general purpose bombs. A given weight of 
small bombs will disrupt a larger area than the same weight of larger bombs, t he voIume of soiI removed being approximate- 
ly the same in either case. For immediate immobilization the number of hits is more important than the size of the cra¬ 
ters, but for equal number of hits large bombs are preferred. 

WEAPON SELECTION: Plane loading characteristics influence the choice of bomb as foI Iows: Multiply the crater area listed 
in the table by the number of the corresponding bombs that the plane can carry, and choose that bomb giving the largest 
total area. The height of release and recommended fuzing are to be read from the table. The number of hits required is 
given in paragraph 2 below. 

RECOMMENDED FUZING AND CRATERS EXPECTED FOR GP BOMBS DROPPED ON UNPAVED AIRFIELDS FROM ALTITUDES ABOVE 3000 FEET 
(For paved areas, the minimum altitude must be 4500 ft to avoid ricochet; the crater dimensions will be about 10% smaller) 


Genera I 

Fuze dela; 

/, sec. 

Crater 

Crater 

Add. Volume 

Area Cratered -f- 

Purpose 

Unpaved 

Paved 

Diameter 

Depth 

to Refill 

Weight of 

Bomb 

Bomb 

Runways 

Runways 

feet 

feet 

crater ,cu. yd. 

sq. ftl bomb 

acres 1 ton 

100 -lb, 

AN-M30 

0.01 or 

1 onger 

0.025 or 
longer 

16-18 

4-5 

15-23 

230 

0.092 

250-lb, 

AN-M57 

0.01 or 

1 onger 

0.025 or 
longer 

21-24 

5-7 

35-55 

400 

0.070 

500-lb, 
AN-M43, M64 

0.025 or 
longer 

0.025 or 

1 onger 

27-31 

6-9 

70-110 

640 

0.056 

1000 - 1 b, 
AN-M44, M65 

0.025 or 
longer 

0.025 or 

1 onger 

35-40 

8-11 

140-230 

1050 

0.049 

2000 -lb, 
AN-M34, M 66 

0.025 or 

1 onger 

0.025 or 
longer 

44-50 

10-14 

290-460 

1680 

0.037 


1. Cratering 

For general purpose bombs dropped from any altitude above 3000 feet and fuzed 0.01 seconds or longer delay, the craters 
in most airfields do not differ appreciably from the optimum. The additional soil required to refill a crater to com¬ 
paction varies in individual cases, but on the average 350 cubic yards of soil per ton of GP bombs or about 1000 pounds 
of soil per pound of explosive are required to refill craters. 

If the drainage of an airfield is known to be poor and the water table high, large bombs with long delay fuzes result 
in deep craters partially filled with water which are difficult to repair. 

2. Number of Hits 

A statistical study of widely varying data on runways 200 to 300 feet in width shows that 8 hits per thousand feet of 
runway length render the runway temporarily inoperative and 5 craters per thousand feet usually leave the strip service¬ 
able. Operational data from the SWPA are in agreement with this study and show that the number of hits rather than the 
size of bomb is the controlling factor. 

3. Repair Time 

Airfields made inoperative by bombing attack can be made serviceable in a short time by repairing the cratering damage . 
Japanese engineering records show that when heavy equipment is used an average of 125 man-hours was required to repair 
craters resulting from 100—Ib GP bombs. 

The use of mechanica I obstacles, small fragmentation bombs with anti-disturbance fuzes, and general purpose bombs with 
very long delay fuzes is recommended for increasing repair times, but should be considered as additional to the minimum 
requirement of 8 craters per thousand feet of runway length. 


EWT-lc (0SRD Report No. 4918) 
July 1945 


f'OKFIDENTiai 


445 




























WEAPON DATA 


AIR ATTACK ON RAILROADS 

The components of a rail system vulnerable to bombing attack are rail lines, rol¬ 
ling stock, locomotives, and marshalling yards. Small GP bombs (100-lb, 250-lb 
or 500-1 b), fuzed 0.01-sec delay, are the most eff ic ient for attacking rail lines. 
The 500-lb GP bomb, fuzed instantaneous or 0.01-sec delay, is the best weapon for 
attacking rolling stock and causes heavy damage if it strikes within about 20 ft 
of a box car or locomotive. The 1000-lb GP bomb fuzed 0.01 sec delay is slightly 
less efficient against box cars and slightly more efficient against locomotives. 
The MAE for damage to rolling stock is 0.29 acre/ton for 500-lb GP bombs. 

Strafing and rocket attack of 1ocomotiveswi 11 result in damage requiring I to 35 
days and I to 60 days, respectively, for repair. Hits with rockets, however, are 
extremely difficult to attain, and of the two methods strafing is probably to be 
preferred. These methods are of little use against other forms of rolling stock 
or against other railroad installations. 

The optimum over-all damage to marshal 1ing yards is caused by the 500-lb GP bomb, 
fuzed 0.01 sec. A density of 1.5 to 2.0 ton/acre on the target is sufficient to 
completely disrupt a yard. 


Table I EXPECTED RESULTS OF DIRECT BOMB HITS OH TRACKS ON THE FLAT 


Bomb 

Fuze Delay 
(sec) 

Radius 
for 

Damage 

(ft) 

Vulnerable Area 
per foot of 
Single Track 
(acre/ton) 

Average Time 
for repair 
(hr) 

Size 

(ib) 

Type 


100 

GP 

0.01 

7-9 

0.0080 

4 

250 

GP 

.01 

9-12 

.004-2 

6 

500 

GP 

.01 

12-16 

.0029 

8 

1000 

GP 

.01 

18-23 

.0020 

13 


Table II APPROXIMATE RADII OF DAMAGE DETERMINED FROM FOUR CATEGORIES 

OF DAMAGE TO LOCOMOTIVES 


Bomb 

Radius of Damage for Given 

Degree of Damage (ft) 

S ize 


Type 

Destroyed 

1000 to 3000 

250 to 1000 

Up to 250 

(ib) 



man-hours 

man hours 

man hours 




for Repair 

for Repair 

for Repair 

500 


GP 

20 

23 

26 

29 

1000 


GP 

40 

44 

48 

52 



Ref: EWT-2d 
August 1945 


446 




















WEAPON DATA 


BOMBING OF BRIDGES 

Ttie table gives Domb and fuze selections for bridges with spans 
next smaller size bomb may be used. For heavy long span bridges 


'> 


(> 1 

^ * BOMBING 

ATTACK ON BRIDGES 


of 100 to 300 feet. For light bridges with short spans the 
larger bombs are often necessary. 


BRIDGE 


BOMB RELEASE 


COMPONENT 
TO ATTACK 


BOMB 


FUZING 


STEEL: 


SIMPLE 6IRDER 

mm 


: 1 1 1 1 n 1 u 1 i i 

i i i i i i i i rrrj 

J__ 



CONTINUOUS GIRDER 


s£ 



SIMPLE TRUSS 


—m £ 


min. altitude 
low dive or 
glide 


piers or abutments 

piers preferred if 
vulnerable 


Largest bomb F/B can 
carry to target. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


M CONTINUOUS TRUSS 





CANTILEVER TRUSS 



high altitude; 
med. altitude; 
high dive or 
gl ide 


superstructure and 
piers in less than 
10 feet of water 
preferred target 
except for multiple 
short-span bridges 


1000 GP single track 
8-i8 ft width 
2000 GP double track 
18ft. or wider 


0.01; Nose 
0.01: Tai1 


piers 

preferred for mul¬ 
tiple short-span 
bridges 


See TABLE A 


8-15 sec. 
or longer 



ARCH 

REINFORCED CONCRETE: 


E 


SIMPLE GIRDER 


r— 


— 

a i 


m CONTINUOUS GIRDER 



ARCH open spandrel, nb or barrel 


ft 

THRU 4 
TYPE 


min. altitude 
low dive or 
glide 


piers or abutments 

piers preferred if 
vulnerable. 


Largest bomb F/B can 
carry to target. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


high altitude; 
med. altitude; 
high dive or 
glide 


superstructure 

preferred target 
except for multi¬ 
ply short-span bri¬ 
dges 


1000 GP single track; 

8-18ft width 
2000 GP double track; 

18 ft. or wider 


Inst; Nose, 
Non-delay; Tail 

for trusses or 
girders < 10 ft 

deep . 

0.01; Nose, 
Non-delay; Tail 
for trusses or 
girders > 10 ft 
deep. 


piers 

preferred for mul¬ 
tiple short -span 
bridges 


See TABLE A 


8-15 sec. 
or longer 


A 

i 1 1 1 1 irn^TrrTTTTMl 1 1 • 

.Illw 

-T- - 



STEEL SUSPENSION 


min. altitude 
low dive or 
glide 


•high altitude; 
med. altitude; 
high dive or 
glide 


piers or abutments 

often too massive 


superstructure 


Largest bomb F/B can 
carry to target. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


1000 GP if less than 
16 feet wide 
2000 GP if more than 
16 feet wide 


Inst; Nose, 
Non-delay; Tail 


"S--" 


. 

i nmi 1 1 h ■ iii i; 1 1 iri iiti 11 




T\] L/N /TJ 


min. altitude; 
low dive or 
glide 


tower footings 


Largest bomb F/B can 
carry to target. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


STEEL TRESTLE 


high a 11it ude; 
med. altitude; 
high dive or 
glide 


superstructure, 
tower, and foot¬ 
ings 


1000 GP single track 

8 - 18 ft. width 

2000 GP double track 
18ft. or wider 


0.01; Nose 
0.01; Tail 



min. altitude; 
low dive or 
glide 


trestle piles 


Largest bomb F/B can 
carry to target. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


high altitude; 
med. a 11.;high 
dive or glide 


trestle,super¬ 
structure, and 
pi les 


500 GP single track 
1000 GP double track 


0.01; Nose 
0.01; Tai1 


ARCH - SPANDREL FILLED 



min. altitude; 
low dive or 
g I ide 


p iers 


Largest bomb F/B can 
carry to target.. See 
Tables A&B for smal¬ 
lest effective bomb. 


8-15 sec. 
or longer 


MASONRY 


CONCRETE 


high a 11it ude; 
med. altitude; 
high d ive or 
g I ide 


superstructure 


1000 GP single track 
8-i8ft width 
2000 GP double track 
18ft or wider 


.01 or.025;Nose 
.01 or.025;Tail 


TABLE A. BOMB SELECTION FOR BRIDGE PIERS 


TABLE B. BOMB SELECTION FOR BRIDGE ABUTMENTS 


| Pier sizes , ftxft + 

5x15 

00 

X 

o 

12 x 30 

15 x 50 

Bomb selection ♦ 

500 GP 

1000 *GP 

2000 GP 

2000 GP 
ineffective 


Average thickness 
of abutment, ft + 

3 to 8 

. 

8 to 10 

10 to 12 

g re ate r 
than 12 

Bomb se1ection ♦ 

500 GP 

1000 GP 

2000 GP 

2000 GP 
i neffective 


EWT—3j(0SRD Report No. 5176) 
July 1945 


447 






































































































































































































































































WEAPON DATA 


BOMBING OF TUNNELS 

1. A tunnel is a good bombing target only if: 

a. The portion attacked is located in broken, weak rock or poor unconsolid¬ 
ated overburden, structurally weak. 

b. It is lined with a structural material reasonably vulnerable to bombing, 
such as timbering, standard tunne 1-liner segments, reinforced or mass con¬ 
crete of not too great thickness. 

2. Tunnels are best attacked by detonation of a bomb in the soil near the tun¬ 
nel lining after it has penetrated from the surface of the ground through the 
overburden (where this is possible). This type of attack requires a bomb and 
altitude of release combination such that the bomb will penetrate to within 
the lethal distance from the tunnel lining. 


LETHAL DISTANCE OF BOMBS AGAINST TUNNEL LININGS 


BOMB 

size, type 


LETHAL DISTANCE, 

ft 



SI ab or Shal low A rch 

or Massive 

with Some Reinforcing 
Concrete Lining 

Pressed Steel or 

Cast 1ron Segments 

Thickness, feet 

\ 

2 

3 

4 

1 

2 

3 

4 

100-1b, 

GP 

10 

9 

8 

6 

5 

3 

20 

250-lb, 

GP 

15 

13 

12 

9 

8 

6 

25 

500-lb, 

GP 

21 

27 

16 

12 

10 

9 

30 

500-lb, 

SAP 

16 

14 

13 

10 

8 

7 

25 

1000-lb, 

GP 

32 

24 

21 

17 

15 

13 

40 

1000-lb, 

SAP 

24 

29 

17 

13 

1 1 

10 

35 

2000-lb, 

GP 

45 

37 

30 

24 

20 

18 

50 

2000-lb, 

SAP 

30 

24 

21 

17 

15 

13 

40 

12000-lb, 

GP 

95 

80 

70 

52 

44 

29 

90 

22000-lb, 

GP 

225 

100 

go 

67 

57 

51 

105 


Values in italics are extrapolations 


3. The vulnerable area will be greatest if the penetration is to the level of 
the tunnel. The fuzing should be a delay of 0.1 sec for deep tunnels or 
whatever is required for this penetration for shallow tunnels. This attack, 
which may call for an SAP bomb to penetrate difficult strata, requires a 
knowledge of the overburden and cannot be used against deep tunnels.Against 
tunnels under rivers or canals, the bomb must pass through the depth of the 
channel and then penetrate into the soil or else form a crater large enough 
to reach the tunnel lining. 

4. Advantage may often be taken of the steep slopes usually present at tunnel 
portals to cause considerable landsl ides, thus blocking the tunnel entrance. 
This type of attack is most efficiently carried out by smaller bombs on the 
basis of results per unit weight of charge, but, bomb for bomb, a 1arger one, 
in general , wi 11 produce a somewhat greater si ide. The probability of strik¬ 
ing the target is increased by dropping the larger number of smaller bombs. 
The fuzing for this attack should be that required to produce the largest 
crater, 0.1 sec or more for the larger bombs and 0.025 sec for the 100- or 
250-lb GP bombs. 



Ref: EWT- 2 c 
August 1945 



































WEAPON DATA 


mm 


Pn wnw; 


§ 


BOMB PERFORMANCE 

12,000-lb GP, TIO AND 22,000-lb GP, T14 


1 


A1 

PERFORMANCE: 


12000-lb GP 4 22000-1b GP 



12,000-lb 6P, TIO, 
United States 
"Tall boy-M",Sn tish 


- 150 " 

305 " 


12 . 5 ', 

i25.1V 


22,000-lb GP, Til, 
United States 
"Grand Slam ",British 


12,000-lb GP, TIO (Tallboy-M) 22, OOO-jJ^GP,_TIU (Grand Slam) 


FLIGHT CHARACTERISTICS 

Plane 

Speed, mph 

Altitude, ft. 

5000 10000 15000 20000 25000 30000 

Altitude, /:. 

5000 10000 15000 20000 25000 30000 

- ~ - - 

REMARKS 

Striking Velocity, ftlsec 
Angle of Impact, degrees 

250 

250 

670 

33° 

870 

24° 

1030 

20° 

1160 
17° 

1260 

16° 

1350 

14° 

670 

33° 

875 

24° 

1035 

20° 

1170 

17° 

1275 

16° 

1375 

14° 


HOMOGENEOUS ARMOR: BHN 

Max. Thickness Perforated,in 

250-300 

5.0 

5.5-6.6 

c c c c Estimated max.for 

o.o-o.o no ca9e br eak-uD 

6.4 

7-9.0 

7 q a Estimated max. for 
no case break-up 

REINFORCED CONCRETE: 

Concrete 

St rengt h 





Max. Thickness Perforated,/*. 

Inert 

5000 psi 
3000 psi 

6.6* 

7.1* 

8.6 

9.6 

10.1 
11.2 

It .6 

13.3 

12.4 

14.4 

!3.3 

15.6 

8.2 

8.8 

1 1 .0 

12.3 

13.0 

14.8 

IVi 

15.9 

19.0 

17.8 

21.0 

■"Ricochet" is 1 ikely, so these 
va 1 ues may not be rea 1 i zed 

Shaded values indicate zone 
of probable case break-up or 
premature detonation..values 
for 20,000 ft. ray be consi¬ 
dered as 1 imiting thicknesses 

Max. Thickness Scabbed, ft. 
Inert 

5000 psi 
3000 Psi 

10.1 
10.6 

12.2 

13.2 

13.8 

15.3 

15.3 

17.2 

16.2 

18.3 

17.2 

19.6 

12.4 

13.0 

15.3 

16.7 

17.5 

19.4 

19.5 

21.9 

20.6 

23.8 

22.6 

26.0 

Max. Depth Penetrated, ft. 
Inert 

5000 psi 
3000 psi 

2.5 

3.0 

4.4 

5.3 

6.8 

7.1 

7.1 

8.8 

7.9 

9.8 

8.8 

11.0 

3.2 

3.9 

5.8 

7.0 

7.7 

9.5 

9.6 

11.7 

10.4 

13.3 

12.3 

15.3 

Max. Thickness Perforated,/t. 
Impact * Expl. * Scab . 

5000 Psi 
3000 psi 

8.0* 

8.5* 

10.0 
II. 0 

11.5 

12.6 

12.9 

14.7 

13.8 

15.8 

14.7 

17.0 

10.2 

10.8 

13.0 

14.3 

15.0 

16.8 

16.9 

19.2 

17.3 

21.0 

19.8 

23.0 

Max. Thickness Scabbed, ft. 
Impact ♦ Expl. * Scab 

5000 p si- 
3000 psi 

11.6* 

12.1* 

13.7 

14.7 

15.3 

16.8 

16.8 

18.7 

17.7 

19.8 

18.7 

21.1 

14.5 

15.1 

17.4 

18.8 

19.6 

21.5 

21.6 

24.0 

22.?1 

25.9 


Max. Depth Penetrated, ft. 

Impact * Explosion 

5000 psi 
3000 psi 

3.8* 

4.3* 

5.7 

6.6 

7.1 

8.4 

8.4 
10.1 

9.2 
11.1 

10.1 
12.3 

6.0 

6.7 

7.6 

8.8 

9.5 

11.3 

11.3 
13.5 

12.2" 1 

15.1 

14.1 

17.1 

Ave. Entrance Crater Diam.,/t 

3-5000 psi 

27 

30 

33 

35 

35 

35 

32 

36 

40 

42 

43 43 

Back Crater (Scab) Diameter ,/t 

3-5000 psi 

Varies from heavy cracks at scab limit 
to HO ft. when perforated. 

Varies from heavy cracks at scab limit 

to SO ft. when perforated. 

EARTH: Soil Type 





— 








Penetration Depth, ft. 

(With long delay fuze) 

Sand 

Loam 

Clay 

26 

39 

56 

33 

48 

67 

39 

54 

76 

43 

60 

81 

45 

62 

85 

47 

65 

87 

33 

48 

70 

41 

62 

85 

49 

67 

95 

53 

75 

100 

56 

77 

105 

59 

80 

111 

For penetration path Lengtn 
add 20$ to 30% to depth . 
Values are given for uniform 
soi 1 . 

Cratering Effect 

Max. Crater Radius, ft. 

Explosive 

Sand 

Sandy Loam 

Clay 

Sand 

Sandy Loam 

Clay 

Torpex D-l 
Tritonal 

39 - 44 

37 - 41 

45 - 49 
41-45 

50 - 55 
48 - 53 

45 - 51 

44 - 50 

52 - 57 

50 - 55 

62 - 68 

59 - 65 

Performance values in EARTH 
dependant upon explosion, are 
based on estimated ratios 

Max.Apparent Crater Depth,/: 

TPX or Trit 

23 - 27 

25 - 29 

28 - 31 

28 - 33 

31-36 

34 - 38 

Displacement in Clay, inches 

Horizontal: 

Vert ical: 


Distance from Explosion, ft. 

Oi stance from 

Explosion, ft. 

of explosives. 

70 

80 

90 

100 

110 

120 

80 

90 

100 

110 

120 

130 

Torpex D-l 
Tritonal 

21.2 

20.4 

II. 1 
10.5 

7.6 

7.2 

3.4 

3.2 

2.7 

2.5 

2.3 

2.2 

28.6 

27.0 

19.2 

18.0 

13.1 

12.4 

9.3 

8.8 

7.1 

6.7 

5.3 

5.1 

Torpex D-l 
Tritonal 

13.0 

12.4 

8.3 

7.8 

5.4 

5.2 

3.2 

3.0 

2.1 

2.0 


20.6 

19.5 

14.4 

13.4 

9.7 

9.2 

6.3 

6.2 

5.0 

4.7 

3.3 

3.1 

Damage of Underground Piping 

Dist. from Explosion, ft. 

Torpex D-l 
Tritonal 

Cast Iron 

Ceramic 

Cast Iron 

Ceramic 


63' 

60' 

104' 

99' 

77' 

73' 

128' 

121 ' 


Underground R/C Wall Damage 
(Average Soil) 

Max. Thickness of Wall 
Breached, ft.: 
Max. Thickness of Wall 
Heavily Damaged,/:.: 


Distance from Explosion, ft. 

Distance from Explosion, ft. 

Damage wi 11 be greater in wet. 

0 

10 

20 

30 



0 

10 

20 

30 

40 


or clayey soil; Less in loose 

Torpex D-l 
Tritonal 

17 

16 

16 

15 

9 

9 




21 

20 

20 

19 

15 

14 

8 

8 



or sandy soil. 

Torpex D-l 
Tritonal 

25 

23 

23 

22 

16 

15 

8 

8 



30 

28 

29 

27 

23 

22 

14 

13 

8 

8 



UNDERWATER: 

Depth Below Surface of 

Water,/:. 

Depth Below Surface of Water, ft. 


Maximum Bubble Radius, ft. 


90 

110 

130 

150 



90 

no 

130 

150 

170 



TPX or Trit 

50 

48 

46 

45 



62 

61 

57 

55 

51 



Peak Pressure, Lbs/sq.in. 


Distance from Explosion, ft. 

Distance from 

Explosion, ft. 


100 

200 

300 

400 

500 

1000 

100 

200 

300 

400 

500 

1000 


Torpex D-l 
Tritonal 

3050 

2730 

1360 

1210 

850 

760 

630 

565 

500 

445 

220 

198 

3700 

3340 

1700 

1530 

1100 

980 

780 

697 

600 

536 

270 

242 


Impulse, l b. msec / sq. in. 

Torpex D-l 
Tritonal 

5290 

5000 

2660 

2560 

1750 

1650 

1350 

1250 

1060 

997 

530 

500 

7950 

7500 

3980 

3760 

2680 

2520 

1980 

1870 

1590 

1500 

795 

750 


air: 














Peak Pressure, lbs/sq.in. 

Torpex D-l 
Tr Itonal 

26 

24 

5.6 

5.3 

3.2 

3.0 

2.1 

2.0 

1.6 

1.5 

0.8 

0.7 

44 

42 

8.2 

7.8 

4.1 

3.9 

2.7 

2.6 

2.0 

1.9 

0.9 

0.9 


Impulse, lb.msec! sq. in. 

Torpex D-l 
Tritonal 

170 

165 

85 

82 

57 

55 

42 

41 

34 

33 

17 

16 

256 

248 

128 

124 

86 

82 

64 

62 

51 

99 

26 

2b 


FRAGMENTATION 






j Thickness Perforsble by Frag- 
! ments at Distance 100 ft, in. 

TPX or Trit 

Mild Steel 

Concrete 

Brick 

Mild Steel 

Concrete 

Brick 


2-3 

18 - 26 

20 - 30 

2i - 3i 

21 - 30 

25 - 38 



SOURCE: Physical Character I at let from Ordnance Department, U.S.Army; Performance Data from various British and American model tests 


PTM No I 16 
June 1945 


449 



















































































































































































































































































* V- 




















































































APPENDIX 


MISCELLANEOUS, INCIDENT SUMMARIES, SOURCES OF INFORMATION 


WEAPON DATA 

SOLAR SHADOW RATIO CHART 

FOR DETERMINING THE HEIGHT OF AN OBJECT FROM THE LENGTH OF ITS SHADOW 

This double page presents a graphical method for determining the height of an object from the length of its 
shadow as measured, for example,on a vertical aerial photograph. The detailed procedure is explained below. 



GCT 

CORRECTION 

degrees 

c 

JANUARY 
to JUNE 


DECLINATION OF 
SUN degrees 

]) 

JANUARY 
to JUNE 



.25 
♦20 
.15 
♦ 10 
♦5 
0 
-5 
-10 
-15 
-20 
-25 


185 

ISO 

175 

♦25 

.20 

.15 

♦10 

♦5 

0 

-5 

-10 

-15 

-20 

-25 


GCT 

CORRECTION 

degrees 

c 

JULY to 
DECEMBER 


{ 185 
180 
175 



JULY 


AUGUST 


SEPTEMBER 


OCTOBER 


NOVEMBER 


DECEMBER 


185 

180 

175 


DECLINATION OF 
SUN degrees 

D 

JULY to 
DECEMBER 



.25 
.20 
♦15 
.10 
♦ 5 
0 
-5 
-K) 
-15 
-20 
-25 


DATA 

The following must be known at the time 
the oeriol photograph was taken: 

I. MONTH and DAY 

II GREENWICH CIVIL TIME (GCT) 

It must be expressed in degrees 
I hr. = 15° 

III. LATITUDE (LAT) ond LONGITUDE (LONG) 
Meosured in degrees 
North LAT is (♦) South LAT is (-) 

LONG East is (♦) LONG West is (-) 



NOTE Shadow length (S) is os measured on 
level ground 

For vertical photogrophs, it is determined 
by meosuring from some point on the object 
(such os o corner of the roof) to the cor¬ 
responding point of the shodow on the 
ground, taking into account the scale of 
the photograph. 


PROCEDURE 

1. Read C on the above graph 

2. Compute the Locol Sun Time (T) 

T = GCT ♦ C ♦ LONG 
NOTE ; If T turns out negative, discard 
the minus sign; 

If T exceeds 360° subtroct 360° 
from it; 

If T still is greater than 180“ 
subtroct it from 360° 

3. Spot T on the bottom scale of the nomo¬ 
gram on the opposite poge (see sketch) 

4. Reod D on the above graph 

5. Compute LAT - D ond LAT + D 

NOTE If either result turns out neg¬ 
ative, discard the minus sign 

6 Spot LAT-D ond LAT*D on the nomo¬ 
gram on the opposite poge — connect 
these points with o straight INDEX 
LINE (see sketch) 

7. From the point for T, project upword to 
the INDEX LINE ond across to the right, 
reoding the value of H/S (see sketch) 


EXAMPLE 

Given: Oote = March 3 

GCT = 2000 Hours = 300° 
LAT = 35° N = * 35° 

LONG = 65° W = -65° 

L C = 177° 

2. T = 300° + 177° ♦ (-65°) = 412° 

412* - 360' = 52° 

3. See sketch of nomogram 

4. D = -7° 

5. LAT-D = 35° - (-7°) * 42° 
LAT. D * 35° . (-7°) * 28° 

6. See sketch 
7 H/S * 0 48 

8. Shodow on photo meosures 9mm 
Scale of photo ; Imm. = 6.2 ft. 
/. S = 9x 6.2 - 56 ft. 

9. Object Height (H) = 0.48 x 56 ft. 

= 27 ft. 


SKETCH OF NOMOGRAM 

LAT-0 LAT‘D 



T = LOCAL SUN TIME 

degrees 


8. Measure shadow length (S) 

9. Object Height (H) * (H/S) x (S) 


452 






















































































































































































































































































































































































































































































































































































































































































































SHADOW RATIO NOMOGRAM 



LAT - D 

degrees 


LAT + D 

degrees 


120 


110 


100 


90 


80 


70 


60 


50 


40 


30 


20 

10 


010 20 30 40 


50 


60 


TT t || I 

70 


80 90 100 no 

T = LOCAL SUN TIME, degrees 


120 


1 t f l 

130 


10 

20 

30 

40 

50 


60 


70 


80 


90 


100 


110 


120 


130 


140 


150 


140 150 160170 

DATE: JULY, 1944 


160 

t'l 80 - 


SHADOW 
RATIO Hfc 
0.00 

0.05 
0.10 
0.15 
0.20 
025 
0.30 
0.35 
0.40 
0.45 
0.50 

0.60 

0.70 

0.80 

0.90 

1.00 

1.25 

1.50 

1.75 

: 2.00 

- 2.50 

- 3.00 
-400 
'500 

-^'lOOO 


CO 



































































































WEAPON DATA 

EQUIVALENT HORIZONTAL AREA 
FOR A SLOPING TARGET 


0 M 2 

EQUIVALENT 
HORIZONTAL AREA 


A| /a 


1.5- 


1.4- 


1.3- 


1.2 — 


l.l 


0.5 — 


0.4 — 


0.3 — 


0.2 — 


0 . 1 - 


0—1 


c 

fiWrgEjj. Line of Approacn 


\ 


_ "ii- Slope" 


i 

i 


V 

A h 

sin y tan a cos 3 ♦ cos y 

A 

l 

1 

1 

i 

l 

l 

i 


A - Target Area 


Line 


-*£-*aar3i £ti _ S!LS r 



Approach Angle 

(down slope approach) 


APP r ° a i-cToP e 

aTTT 0 ' 


EquivaIent Horizontal Area 



EXAMPLE Given:'o * 15°, 6 - 45°, y * 60° 
Find: A h /A 

From intersection of a “15° and 3 * 45° 
follow horizontal line to vertical index 
line, B-B...from the point on B-B draw a 
straight line through y * 60° and read 
A h /A - 0.66 


For the computation of bombing densities, the area of a sloping target must be evaluated 
in terms of an equivalent horizontal area. If we imagine rays of light parallel to the 
path of the bombs striking the target, the area of the "shadow" cast on a horizontal sur¬ 
face is the equivalent horizontal area, A h . 

The nomogram gives the ratio of the equivalent horizontal area, A h , 
area, A, in terms of the angle of impact, a, the angle of approach, 
the target, y. 

If N bombs strike the target area, A, the bombing density on the target is: N/A.the 


to 

3, 


the actual target 
and the slope of 


bombing density on a horizontal surface is: M/A. * (M/A 


y on 

)/(A h 


A h /A). 



3= 90° 


3= 90° 


Approach Angle 

(up slope approach) 


NOTE: 

horizontal lines are 
guide lines only 


3 = 30° 


EWT 3 (PMR 73) 
April 1945 


454 




















































INCIDENT SUMMARY 

MULTI - STORY, STEEL FRAME 

OFFICE BUILDING STRUCK BY A 550 lb. G.R BOMB 


’ A-550] 

l-\. MS-SF 

INCIDENT ONE 

V_II._ 


PF- 5902/14 





EIGHTH FLOOR 


(GERMAN 250 K.g. S.C.? chg. wt. 5 0%| 

BUILDING 

Office Building - basement,sub-basement and eight 
upper floors. 

Construction: Frame - concrete-encased steel frame 
with bolted connections. 

Floor slabs-hollow tile and rein¬ 
forced concrete joists. 

Exterior walls-13^2 in. brick, stone. 
Interior partitions-3" and 4”, some 
4'/2 in. and 9" brick. 


DAMAGE 

Bomb perforated the roof and 8 th fir. near one cor¬ 
ner of the building and exploded just above the 
7 th floor. The extensive collapse of the 7 th and 
8* h floor slabs was due to the failure, on both 
floors, of the connection of beam l at column 
a (see framing plan). This connection provi - 
ded the only interior support for the entire cor¬ 
ner bay floor framing. 

On the 7 th floor, beams 1 and 2 hinged down 
from their connections at the exterior wall. Col¬ 
umns b , extending through the 7 th and 8 th floors, 
were left hanging from the roof structure, whe n 
these supporting beams hinged down. Beam 3 
was deflected downward 3 inches. 

On the 8 th floor, connections at the exterior 
wall ends of beams 2 failed allowing the entire 
floor structure to collapse. Beam 3 was de¬ 
flected upward 4 inches. 

Blast damage to doors and windows extended 
for some distance through building. Exterior walls 
were blown out where shown crosshatched on the 
plans and section. Similarly, partitions shown 
crosshatched were destroyed. 



Note: Circles represent the intercept of sphere of designated 

rodius with the floor in question.the center of the sphere 

being at the estimated position of the explosion. 


March 1943 

















































































































































































INCIDENT SUMMARY 

MULTI - STORY STEEL FRAME 

APARTMENT BUILDING STRUCK BY A IIOO lb. G.R BOMB 



PF 5902/15 


\ 




j all partitions'^ this floor 
i and within 50'of explosion 
' blown out 


PLAN fourth floor 


scale 



20 * 25 ’ 30 * 




fifth floor 


sixth floor 



(Germon 500 Kg S C.chg.wt. 50%) 


BU I LD I NG 

Type: Apartment building cons i sting of base¬ 

ment and seven upper floors. 

Construction: Concrete encased, high tensile 

steel (Chromodor) frame. Floors: 6" hollow 
tile and 3^" concrete including finish; I" 
plaster. Roof: Similar, plus I" asphalt sur¬ 
face. Exterior Walls: 9" brick with outside 
tile facing. Partitions: 3" brick or breeze 
block and 7/8" plaster. 

Girders: G7l-plated, I0"xl2"; others I4"x55 n 
Beams : All beams 5" x 12" I-beams. 

DAMAGE 

The bomb per forated the roof and three floors; 
detonated just above the fourth floor. 

Roof: Punched a 22" hole; no structural damage. 

Seventh Floor: Plated girder, G71 , severed 
by impact of bomb. Approx, areas of damage 
in sq.ft, to: floor - 100; partitions - 400; 
exterior walls - 0. 

Sixth Floor: G6 I buckled, end connections 
were torn but flange held up one end. Approx, 
areas of damage in sq. ft. to: floor - 190; 
partitions - 340; exterior walls - 0. 

Fifth Floor: G5I deflected up 7"; beam B 51 
was bowed out 3", B52 was bowed up and one 
column connection severed. Approx, areas of 
damage in sq.ft, to: floor -650; partitions- 
1500; exterior walls - 230. 

Fourth Floor: G41 blown down; B41 and B42 
were left hanging by far-end connections. 
Wall beamB43, one end torn loose, was wrapped 
back 90°; B44 and B45 were bowed out li"; 
B46, one end torn loose, was bent out. Column 
Cl was bowed 7" and twisted 2". Approx, areas 
of damage in sq. ft. to: floor - 700; parti¬ 
tions - 5000 or all within radius of 50 ft.; 
exterior walls - 400. 

Third, Second, First Floors: Ho structural 


damage. Approx. 

areas 

of damage in sq. 

ft. 

to: FIoor s: 

3rd 

- 

1 50; 

2 nd 

- 120; 1st - 

120 

Partitions : 

3rd 

- 

1000 ; 

2 nd 

- 400; 1st - 

1 80 

Ext. Walls : 

3rd 

- 

360 ; 

2 nd 

0 ; 1st - 

0 

The 5th f1oor 

slab 

was 

blown 

up; the 4th 

was 

blown down. 

The 

s 

ingle 

bay 

of the 3rd, 

2 nd 


and 1st floors undoubtedly collapsed under 
the impact of the debris load. Doors and 
frames along corridors were damaged; all win¬ 
dows around the area were broken. 



«r 


April 1944 









































































































































































































































































INCIDENT SUMMARY 


MULTI - STORY, STEEL FRAME 

RAILWAY STATION STRUCK BY A 3100 lb. A.R 

PF* 5902/17 


BOMB 



(Germon I400-Kg, S . D.,Chg.Wt.-22%,) 



walls ai\d columns blown 
\down are shown cross 
hatched. -^ 


wo l! andtunfiei 
demolidhed^jl 


escalators 


PLAN at basement level 

Scale 

o 1 ' io l 2 o'" 

all doors blown 
out along here 

\ 

brick pier fractured 


new\ I old 
station •*|4 ”station 


—building line at grade 


arch runnel —* ^ 
R/C retaining wall—* 


PLAN at track level 
R/C retaining 
watt 



track level 


SECTION B-B 

brick wall,X-Y y and 


cols, leaning is 0 -, 14 jJ 
mtoct —-j—*fi 

first 


basement 


track level 



piles under col. f igs. 

<1 U-* 


BUILDING 

Type: Railway station ticket office, a recent addi¬ 
tion to existing old station, consisting of one story 
above ground, a basement, and the track-level sub¬ 
basement . 

Construction: Concrete encased steel frame, beam and 
girder system, 6 inch and 7 inch two-way R/C floor and 
roof slabs. Outstanding feature of the construction 
was the very heavy girders (4 ? -2’ I-beams with cover 
plates) spanning the tracks. These girders were sup¬ 
ported by steel columns set on piles and were designed 
to carry a proposed 10-story bui1ding (see exposed col. 
splices shown on sections). Heavy R/C retaining walls 
formed the foundation for the exterior walls of the 
building above grade. The old station was built of 
single girder, steel arches and light lattice purlins, 
covered with a patent glazing and corrugated sheath¬ 
ing. Underground tracks were housed in a five-ring 
brick arch tunnel. 

DAMAGE 

The bomb perforated the street level or first floor, 
struck the girder as shown, and exploded. The girder 
was severely damaged— I-beam badly bent, plates torn, 
8 ’ — 10’ of concrete encasing stripped off, girder de¬ 
flected 4". The other girders were deflected (am't 
shown on plan) and the concrete encasings were exten¬ 
sively cracked. Deflections were apparently caused 
by violent and heavy debris loads. The entire first 
floor and roof slabs were completely demolished. 

A few of the columns and beams remained standing, 
though twisted and bent. The columns and roof and 
floor beams between Y and Z remained standing — con¬ 
nection at Y failed. Failures occurred in the bolted 
connections between beams and columns—apparent from 
the fact that many concrete encased members were strewn 
about but damaged only at the ends. 

The exterior brick walls of the building were blown 
out except between X-Y and Z-W. (See plan at basement 
level.) The wall, X-Y, and integral columns leaned 
outward 15° with the vertical but remained intact. A 
small portion of the brick tunnel was demolished. Ad¬ 
jacent buildings suffered some blast damage. 

Damage to the old station was limited to the removal 
of all sheathing and glazing — no structural damage. 

The bomb was identified by a fragment, 15" x 12" x 3" 
thick in size. Retaining walls suffered some frag¬ 
mentation damage. Damage to the retaining walls and 
girders might have been greater if the bomb had not 
been stopped by the girder. 


Note: Circles represent the intercept of sphere of designated 

radius with the floor in question.the center of the sphere 

being at the estimated position of the explosion. 


September 1943 


457 
































































































































































































































































































INCIDENT SUMMARY 

MULTI-STORY, STEEL FRAME 

OFFICE BUILDING STRUCK BY A PARACHUTE MINE 



PA HA¬ 
SH I jN E 
MS - SF 


1 


INCIDENT ONE 




ELEVATION showing damage 


DAMAGE 

The parachute mine fell in the street near one corner 
of the bu i Iding, forming a crater about 25 ft. in di¬ 
ameter. The structural framework was generally un¬ 
damaged. There was some slight spalling at the junc¬ 
tion of the floor slab and beams at the first floor. 
The slab was undamaged but the second f1oor was broken 
up directly over the blast. 


... The basement walls nearest the crater were covered 
with fine cracks and leaked slightly. Basement par¬ 
titions were demolished and blast damage to doors, 
windows and br ick facing was considerable. Attention 
is called to (A) on the elevation showing the char¬ 
acteristic damage to the face-brick and stone caused 
by the interval of low pressure (suction phase) which 
directly follows the high pressure (positive phase) 
of the blast wave; the facing appears to have been 
sucked from the wall. 


The basement was adapted and used as the A.R.P. central 
control. Wood beams and struts, 3"x9" and 9"x9", were 
insta1 led to support the concrete floor. Some of the 
beams were spl it along the horizontal axis. (See de¬ 
tail of strutt ing.) 


PF- 5902/19 




PLAN showing damage 
basement strutting shown dotted 
Scale: 

0 5 0 10 20 


BUILD ING 

Type: Commercial building consisting of a basement 
and f ive upper f1oors. 

Construction: Concrete encased steel columns and 
beams. First floor slab of 5-inch R/C; upper floors 
of patent hollow concrete slabs. Walls of 13-1/2- 
inch brick. 


Damage to the oil burner lead to localized fires 
throughout the building. 


street 


A- 



[■ 


strutting in bosement 
to 


□ □□□ 



SECTION 



DETAIL OF STRUTTING 



December 1943 



































































































































































































































































































INCIDENT SUMMARY 

SINGLE STORY, STEEL FRAME 

SHED BUILDINGS STRUCK BY IIO lb. G.R BOMBS 



INCIDENT ONE 


^ _ / 



(German 50 kg S.C. ? chg. wt. 50%) 


BUILDINGS 

A group of seven single story, steel framed shed buildings 
and a boiler house with adjoining coal bunkers was the ta* 
get of a stick of nine no lb. G. R bombs. Sheds A, C, E 
F and G measured 504'x 240'x i3'/2' (to eaves ) ; sheds B 
and D measured 252'x 240'x 13'/z. 

Construction : Steel saw-tooth trusses , 40' long space d 
12 ’oc. with timber purlins , and valley beams 36' long 
formed 40'x 36' bays. Columns were 8"x6"rolled steel 
Roof was sheathed with corrugated asbestos cement 
sheets. The lower half of the north face of trusses was 
glazed. Brick walls , 9" thick , had glazing in short, end 
walls and roller shutter doors (IO‘x 12') in long side walls 

DAMAGE 

Bomb no. I ,2,3, and 4 ; see Plot Plan. No damage to build¬ 
ings , killed one cow. 



TT 


Bomb no. 5 ; see Detail l: A crater, 20’in diameter, 3^9" 
deep, was formed at the corner of shed F in the 5" R/C 
road slab.The slab was cracked and lifted for a maximum 
distance of 15'from crater edge. The 9" brick walls were 
cracked by earth shock and the roofing dcmaged by fall¬ 
ing debris to the extenl shown. The shutter doors in the 
side wall were not damaged. 




DETAIL 2 


damage to coat bunker of boiler house by bomb no. 7 



damage to shed C by bombs nos. 8 Q 9 


Bomb no 6 ; see Plot Plan : Damaaed sheds F and G 
by blast, breaking 80% of the end wall glazing and ap¬ 
proximately 57« of the north-light glass in the crossed areo 
The chimney, 130'high, was marked by about6 fragments 
all striking above a point 80* from the ground. 

Bomb no. 7; see Detail 2: Direct hit on unfinished, filled 
coal bunker, Destroyed 13'/z" brick walls and dislodged 
several steel roof joists. Roofing on unfinished boiler 
house was not damaged. 

Bombno.8 ; see plan of Detail 3: Direct hit on shed C, 
perforated roofing and formed a crater 7 Vie' in diameter, 
3' deep , in 6 inch R/C floor slab. Bomb just missed 
valley beam . Only 5 timber purlins were destroyedand 
the valley beam was cut by o few fragments. Stacks of 
picks and shovels were thrown about. Asbestos cement 
roofing was completely destroyed in the shaded areo 
(approximately i7280Q')and less seriously damaged in 
the crossed area. The figures indicate the percentage 
of north-light glazing broken in each 40'x36‘ bay. 

Bomb no. 9 ; see elevation of Detail 3: Bomb hit nearcor 
ner of shed C forming crater 16'-20' in diameter; nearest 
edge 4' from wall. The 9 inch brick wall in thisbay was 
extensively cracked as shown. The front wall (at left)was 
moved out over one inch , sliding on its damp-proof course. 
There was some roof damage evidently caused by debris. 
No fragmentation damage. Approximately 80% of the 
end wall glazing in this shed was broken by bombs 
no. 8 and 9 . 


May 1943 







































































































































































































INCIDENT SUMMARY 

SINGLE STORY, STEEL FRAME 

FACTORY BUILDING STRUCK BY 2-550 lb. G.P BOMBS 


u 


I - 550 

SS-SF 

INCIDENT ONE 


PF- 5902 / 21 


(GERMAN 250 kg. S C. chg wt. 55 %) 





T W 2 X 3 L ) 2 teX 2 L 

j'/Z" wire mesh 


9 "X 7 "6o!s 


'SECTION A-A BEFORE 


main truss twisted as 
well as deflected 


joint failed 


SECTION A-A AFTER 


BU I LO I NG 

Type: Single story factory building form¬ 

ing part of an industrial complex. 
Dimensions: l 8 l'- 6 " x I I 5 ' - 6 " 

Construction: Outside walls are of brick. 

Trusses span the I I 5-f t. width of the build¬ 
ing and are supported on the west side by 
9 n x7" steel columns, and on the east side by 
girders spanning 90-ft. door open i ngs . Saw¬ 
tooth trusses, spanning 30 ft. and spaced 
11.5 ft. apart, were supported on the I I 5-f t. 
trusses. North and south end wal1s supported 
the ends of the saw-tooth trusses. Roof 
covering was asbestos sheets supported on 
steel angle purlins. Ridge plate was of 
timber. North lights of saw-tooth trusses 
were enclosed with i" wire glass. 

DAMAGE 

The two bombs perforated the roof and exploded 
upon contact at the floor. The explosions 
lifted truss Tland severed its connection 
with column 4-. That end of truss subsequently 
collapsed. Three baysofthe brick wa 1 1 were 
blown down; the saw-tooth trusses, supported 
there , collapsed . 

The saw-tooth trusses along section A-A op¬ 
erated as a chain of tension members allow¬ 
ing a decreasing amount of sag toward the 
outside walls. The amount that each truss 
shifted toward the center is shown on the 
section. All saw-tooth trusses east of sec¬ 
tion A-A acted similarly but to lesser de¬ 
gree. Columns 3 to 8 were bent toward the 
collapse, varying in amount from 3 " to 5 ". 

The chain of tension members depended on one 
bolt for its support. However, if it had 
failed it is probable that the next line of 
trusses would have taken the load with a 
correspondingly greater amount of secondary 
col lapse. 

All asbestos roofing and glazing were blown 
off. In general, the purlins remained in 
place prevent i ng the l ateral collapse of the 
saw-tooth trusses. In the area over the 
blast, however, the purlins collapsed with 
the trusses. 

One bay of a platform, which was independent 
of the main structure, was blown down and 
the ad joining bay was bad 1 y bent and def 1 ected 
by the blast. 

The I 5 " wire mesh which had been attached to 
the bottom chords of the trusses caught most 
of the debris from the roof (except in the 
area over the blast) and prevented many cas¬ 
ualties. 


ISOMETRIC of 
damaged building 

dotted lines indicate former position of trusses A-A,T3 ,T4 


<4<N0RTH 


PLAN scole 


TRUSS T 3 


TRUSS T 4 


former position of truss 
shown dotted 


-steel frame platform 
damaged by blast 


platform knocked 
down by blast 


March 1944 














































































































































INCIDENT SUMMARY 

SINGLE STORY, STEEL FRAME 
FACTORY BUILDING STRUCK BY A 2200 lb. G. P BOMB 

PF-5902/23 (GERMAN 1000 K.g. S. C. ? Chg. wt. 50 %) 


J> SS-SF 

INCIDENT ONE 



l roof structure 


putted toward 


collapse (esoo 6 ’^ 


buildings this side, 
of 4 wall ondamog&i 
except roofing j 
destroyed here^ I 




i^bistructufe 
collapsed in ti 


upper 6' of 
’•ytott felUst: 
I ward bomb 


*■»■«■*■*■* 


of roof structure 


this line of cols. 
♦<f girders wos 


ereuspo'*} 


undamaged 


roof structure 


putted toward 


i collapseptbOQrO') 


9" brick wo It, to' high cracked 
near top as whole wall, incl. 
cols., was pulled in by roof 
collapse 


some g.i. sheathing 
remained intact on 

^ SSSs ss sass ^this wall 



SECTION A-A 


BUILDING 

A90'x225'fully-framed steel shed. Asbestos cement 
sheathing on steel Z purlins. Monitored roof truss¬ 
es spaced at 12^2* on 45’spans carried by braced 
valley beams. Beams span 25' between columns. 34' to 
tie level. Columns have extra legs to carry crane gir¬ 
ders ot 24 1 level (see sec.A-A),and stand on concrete 
blocks set on reinforced concrete piles. 


DAMAGE 

Bomb hit crone girder l-l and exploded below level of 
col. footings. Cols. 1,1 and crane girders 2-1,l-l ft 1-2 
were blown upward. The col.footings were stripped 
from their piles and the girders were torn upwards 
from their connections. Valley beam 2-I-I-2 alsocame 
down ond with it all of the roof structure within the area 
shown by the heavy shading. The adjacent roof structure, 
within areas shownin heavy shading atedge,was pulled 
toward the collapsed area. At the top of the wall at 
the river end of the building (R-R) this amounted to 
approx. 3'-4'.The top of col.3(between crane girder ft 
roof) was bent inward about 4"-5". The lighter cols.4, 
5 ft 6 bent inward approx. 3-4' with the wall but re¬ 
mained vertical at bases. The crane girders that 
fell remained virtually undamaged, failure occurring 
within the bolts of the connections rather than the 
members. The chimney, collapsed by earth-shock 
and blast, crashed through the roof carrying with 
it a considerable portion of the roof structure. 


All of the glazing and all g.i. roofing in entire 
building gone. Many purlins and light roof mem¬ 
bers were bent and twisted-their connections al¬ 
so suffering. All exterior wall sheathing, except 
in end wall R-R,also gone. Attention is called to 
the displacement of the col. footing (see sec.A-A) 
It is to be noted that this block of concrete was 


securely anchored to the R/C piles. 



March 1943 




















































































































INCIDENT SUMMARY 

SINGLE STORY, STEEL FRAME 

FACTORY BUILDING STRUCK BY A PARACHUTE MINE 


r 


v. 



PF-5902/24 



“2 STORY 


BUU-DING 


Crone 


utted 


area 


'^assumedpath of mine 


PLAN 


crane 

girders 


BUILDING 

Type: Single story, steel frame main shop of a steel 
mill; approximately 375 ft. x 500 ft. 

Construction: Interior columns (affected area) - 
heavy, lattice type; one leg consisting of 3 - I5"x6" 
I @ 59# with 2l"x7/8" cover plates and the other leg 
of 2 - I6"x6 n I @ 42# with I4 "x 5/8" cover plates. 
These legs were laced together with steel angles and 
spaced 5 ’ -7 1/2" o.c. A single built-up col umn extended 
upward to the roof and was centered on the lattice 
column cap. 

Girders and Trusses - crane g i rders, about 5'-6" deep 
spanning 46'-9" between columns, ran the full length 
of the building on each side of the columns. They 
were bolted thru their bottom flanges to the column 
caps. Above these a third crane girder, facing the 
Casting Bay, was supported on brackets from the center 
column. Longitudinal flat trusses, also attached to 
this center column carried the light pitched roof 
trusses. 

Roofing and Sheathing - corrugated galvanized iron 
sheets, secured by 5/16" hook bolts toside rails and 
purlins. The side rails and purlins were 3 l/2"x 
3"x3/8" angles. 

Two-story Building - br ick wal1-bearing construct ion, 
about 20 ft. x 180 ft., R/C floor slabs, roof of R/C 
ribs and hollow tile filler. 

DAMAGE 

The parachute mine perforated the roofing and fell 
close to the lattice column, detonating upon contact 
with the floor. Only slight structural damage was 
done to the ma i n shop building. The'column nearest the 
explosion was distorted considerably: one leg, con¬ 
sisting of three l-sections, was sheared off at the 
base: the other leg, two l-sections, was almost severed. 

Crane girders I, 2 and 3 (see plan) were blown down 
when their bol ted connect ions fai led in tens ion. Gird¬ 
ers 4, 5 and 6 were torn loose but did not fall down. 
A few roof pur 1 ins and truss members were bent and torn 
loose by the fall ing mine. No roof trusses came down. 

Almost a 11 of the roofing and wal l sheath ing was blown 
off of the bui1ding. The hook bolts straightened out 
but did not tear out of the sheathing. 

The two-story brick building, adjacent to the Ladle 
Stockyard suffered cons iderable damage. The roof slab 
and second floor walls were completely demolished by 
the blast. 


SECTION A-A 


2~t6 m X6"l’s e 42*t 
2 cover plates 14 X fyg 


lacing torn off 


column teg nearly 
sheared off 



3-t5"X6"ls € 59# m 
2 cover plates2t X fts 


column teg 
sheared off 


DETAIL OF 
COLUMN DAMAGE 


January 1944 














































































































































































































































































INCIDENT SUMMARY 

TWO STORY, REINFORCED CONCRETE FRAME 
SCHOOL BUILDING STRUCK BY A IIO lb. G.P BOMB 


t - 

r 

HO 

X. jX 

MS-RCF 

INCIDENT ONE 


PF-5902/25 



GROUND 
FLOOR PLAN 


I floor slob broken 
and hanging down 


scale 

S o s to 


12 persons shelter¬ 
ing here were 
uninjured 


boiler moved l" and 
damaged 


BASEMENT 

PLAN 


(German 50 kg. S.C. chg. v»t. 50%) 


BUILDING 

Tyoe: School building consistingof basement 
and two upper floors inarea affected by bomb. 
Construction: Reinforced concrete frame.Flo or 
slabs 5" concrete. Basement 18" brick walls, 
exterior walls above basement 15" brick. 
Partitions 45 " brick. 

DAMAGE 

The bomb perforated the roof and two floors 
detonating in the basement. Structural dam¬ 
age was confined to the boiler room (7000 
cu. ft.) in which the explosion occurred. 
The bomb exploded in the 45 ft. soace between 
the boiler and the heavy outside wall. The 
first floor beams (Bn; 1,3,4, and 5) were 
raised upward. Floor slab over Rml, having 
pulled away from its 45 -in. bearing along 
the wall, was broken and left hanging down. 
The floor slab over beams Bm3, 4, and 5 was 
also raised but beam Bm2 remained in place 
being supported by the 1 st. floor partition. 
A hole (about 85 sq. ft.) was blown in the 
floor slab immediately over the blast. 

Other damage to the building was minor, con¬ 
sisting of an il-in. diameter hole in the roof, 
a smal l portion of the parapet wal 1 demol ished, 
an II" x 19" hole in the second floor and 
some glass damage. A few days after the inci¬ 
dent the school was in normal operation al¬ 
though no repairs had been made in the mean¬ 
time. 

Two casualties resulted on the stair when 
a door was pulled down on top of them. The 
boiler and chimney effectively screened 12 
other persons sheltering in the basement. 

The sketch below shows the broken connection 
of beam BmI to column I and is typical of con¬ 
crete beam and column fracture under uplift 
loading. 



May 1944 



463 



































































































































































































































INCIDENT SUMMARY 

THREE STORY, REINFORCED CONCRETE FRAME 
WAREHOUSE STRUCK BY A 5501b. G.P. BOMB 


MS-RCF 

INCIDENT ONE 

_—_ J 


PF-5902/26 



roof 6 third ft. 
slobs undomoai 


concrete stripped 
from beam (2m •— 7 


second 


cone spalled 
from column I 


roof 


third 


n 

0 first 


wood deck 



[steel chdnm 
^boltedto be 


brick pier 
crocked 


\ six botsft&O*'} of second 
\ 1 4■ooirciob coBopstoffis this O*S0 \ 


brick piers 
crocked 


( ' 9”brick wall 7 

buckled & crocked 


} oB first 6. second , 

, ft. metol roller drs) 
blown out ot this \ 
< wa tf - -► ) 


9" brick wail 
blown down 


SECTION A-A 


PLAN __ 

showing damage to first and second floor 


(German 250-kg. S.C.’ Chg. Wt. 507.) 


BUILDING 

Type-- Wharf warehouse* first,second and third floors* 
brick vaulted cellar under back row of bays Overall di¬ 
mensions 45x130'. 

Construction.- Reinforced-concrete frame, beam and 
slab, I3'x 15' bays. Slabs- 8 k 2 " thick,designed foralive 
load of 336 Ibs.per sq ft .(3 cwt). Columns-first floor 
24" x 24", second fl.-2l"x2f, third fl- I8"xl8". 

At the time of the incident the first fir. was loaded to 
within 12 " of the ceiling with crates and barrels of 
eggs, cheese and packinq material. The second fir. 
was not loaded* the third floor was loaded. 

DAMAGE 

Bomb perforated roof and two floor slabs and deto¬ 
nated centrally in plan at the first floor, forming a 
small crater in the solid floor. Due to the muffling 
effect of the goods on this floor and the ease of 
lifting the unloaded second floor, the force of the 
blast was upwards. No damage due to fragmentation. 

The entire second-floor slab (5950 Q, )was lifted and 
torn from its supporting beams. Six bays (H70 D, )of 
the slab directly over the explosion collapsed. The 
slab crocked parallel with the one-way reinforcing 
and remained lifted along lines indicated thus;——' 
and sagged along lines indicated thus:---'”. Max¬ 
imum lift occurred along the brick wall at tne rear 
of the building. Maximum final lift was 17" Roof 
and third-floor slabs were not damaged. 

The beams lifted with the slab and failed in reverse 
bending, stirrups pulled out and concrete cracked 
from reinforcing as shown in sketch below. All sec¬ 
ond-floor beams suffered similar damage in vary¬ 
ing degree. Beam (B) had concrete stripped from 
steel to the extent shown on plan and section. 

Column (a), 2 feet from the bomb, had a ‘/i 6 " metal 
guard blown away and concrete spalled from its 
base to a depth of 9" and to a height of 2 ‘- 6 ". No 
other column damage except light tension cracks 
at beam haunches. 

Wall damage is shown cross-hatched on the plan. 



TYPICAL BEAM and SLAB FAILUR 


E 


May 1943 







































































































































INCIDENT SUMMARY 

TWO STORY REINFORCED CONCRETE FRAME 
TEST BUILDING STRUCK BY A IOOO lb. G.R BOMB 

PF- 220l/l2 , vols 1-5 


GpToool 

MS-RCF 

INCIDENT ONE 



KEY PLAN complete building 


AREA 

FIRST FL 

SECOND FLOOR 

ROOF 

EXTERIOR CURTAIN WALLS-2nd FLR 

NW 

o 

\ 

cr 

>N 

o 

7 inch slob, 2 -way R/C 
on concrete beams 

3xiO wood rotters on steel 
beams, l“wood sheathing, 
asbestos cap, 4-ply felt rfg. 

NW-w: 2X4 studs. 
7/e"shtg,7/»“ clap¬ 
board, wood sash 

NW-n: i 2 " brick, 
steel sash 

NE 

* o 

-a 

0 " flat slob,2-way R/C 
on column capitals 

20g steel rib roof,steel beoms 
a girders ,'/ 2 “ insul, 4-ply rfg. 

NE-n: 8“ brick, 
steel sash 

NE-e: 8“ concrete 
block, steel sash 

SE 

■§ 5 

ri 

S3 

3“ Slab (exp'd metol reinf.) 
on R/C joists 02“x2Cf 
pons) 

2“Slab(exp'd metal reinf.)onR/C 
joists(6“x20"pans), 4-ply felt 
rfg. promenade tile surface 

SE-e: i 2 " load-bear¬ 
ing tile, steel 
sash 

SE-s- 12" brick, 

steel sosh 

sw 

« o 

CD 

C 

o 

4"slob (exp'd metol reinf) 
on R/C beoms(5'-0"o.c) 
and girders 

20g. corr g.i. roofing on steel 
saw-tooth roof trusses, north- 
light wire-glass lights 

SW-s 20g corr g.i. 
on steel frame, 
steel sash 

SW-W: 20g.corr g.i. 
on steel frame, 
steel sash 




ELEVATION NW-n 
12 “ brick 


■ . .. '-- J " -—-- 



<rv 

r\ 



n 

• 



frTi 

k_j 

- rr 

r— •' 

" * 

n 

/ 

i 

- II - M - 1 

r '" "“I 

i 


ELEVATION SE-e 
12* til* 


ELEVATION NE- 
8“ concrete block 


-- 

1 


—- 

1 

t . 

1 


l 

« W 

fvr 

1 1 

f 

i-il-1 


i-1 


BOMB 

Americon looo-lb.M44G.P. bomb chg wt. 56% Dropped 
from on altitude of 4000 ft. Impact velocity-529 ft./sec. 

BUILDING 

a two-storv reinforced-concrete framed building proto¬ 
type, zoo'* 200'. divided info four areas, too'xioo', each 
employing a different type of second floor, curtain woll 
ond roof construction as described in detail in the table 
at the left The floors were designed to corryalive load 
of 200 lbs per sq.ft. The columns, 26"x26" containing 12 - 
i‘/4“ round bars, were spaced 20 ft. on centers through¬ 
out the building Curtain walls were built at the second 
floor only. 

DAMAGE 

The bomb perforated the roof, centrally In plan of oreo 
NW, ond detonoted high order at the second floor 
level about one foot from column ©. 

Roof: Major damage occurred in oreo NW where approx. 
6400 sq ft of the wood roof ond steel supporting struc¬ 
ture was completely destroyed. The remaining 3600sq. 
ft of rfg. in this area was dislodged but the structure 


(rafters and beams) remained intact. In area NE ap¬ 
prox. 600 sq.ft, of the steel rib roofing was blown off 
and the rest shifted 6 in. toward the bomb. The steel 
beams and girders remained intact. Minor damage oc¬ 
curred olso in area SW where about iooo sq.ft, of 
corrugated galv. iron rfg. was completely blown off of 
the steel saw-tooth trusses and about 9000 sa ft. 
of the roofing was buckled and torn loose. Saw¬ 
tooth trusses and purlins were not damaged Ap¬ 
prox. 40% of the north-light gloss wos broken. The 
only damage to the roof of area SE was slight fail¬ 
ure in reverse bending as indicoted by typicaldiog- 
onol crocking of about 50% of the roof joists. Sixty 
feet of the parapet wall between areas NWondSW 
was bulged southward and about is sq.ft, of brick 
knocked out. 

Second Floor: Column (o) was destroyed and o 7-ft. 
section blown 27 feet awoy. A 9-foot hole wos 
formed in the floor slab. Columns (B) received mo- 
jor fragmentation damage consisting of spoiling of 
concrete (from 2 to 6 feet) and exposing reinforcing. 
The wood curtain wall, NW-w, wos completely de¬ 


molished The 12 -in. brick wall, NW-n, was cracked 
and bulged, oil glass blown out. The 8-inch brick 
woll, NE-n, was cracked and bulged to a little 
greater degree and most of the glass blown out. 
The B-in. concrete-block wall, NE-e, was bulged out¬ 
ward from one to three inches. Of the masonry walls, 
the i2-in woll of lood-beoring tile. SE-e , was damoged 
the most. About 10-20% of tnis wall was blown 
out and about io% was spalled off inside. The 12- 
inch brick wall, SE-$, was virtually undamaged, suf¬ 
fering only a few small fragment hits and bending 
of oil window sash. The corrugated galvanized iron 
curtain-woils, SW-s ond SW-w, were blown out-, the 
steel framework and windows were not damaged. 

First Floor: The top 6.5 feet of column (a) were 
shattered by the bomb. An area of obout 600sq.ft, 
of the first-floor slab was blown out. 

Not* Circles rsprsssnt the intercept of sphere of designated 
radius with the floor in question the center of the sphere 
being ot the estimoted position of the explosion. 


May 1943 












































































































































































































































































INCIDENT SUMMARY 

MULTI-STORY, REINFORCED CONCRETE FRAME 
APARTMENT BUILDING STRUCK BY A IIOO lb. G.R BOMB 

pc_ 5902/5 (GERMAN 500 Kg.S.C.chg.wf. 50 %) 




ELEVATION A 
roof 
ninth 
eighth 
seventh 
sixth 
fifth 

ELEVATION B 
roof 

ninth 

eighth 

seventh 

sixth 

fifth 

SECTION AA 
roof 

ninth gf-tf 

eighth 9-6" _ 

seventh 9- 

sixth 9 -£l_ 

fifth 9 '-&l 



H 



1 


p: 

laTWoo 







: I; 



M 

L 


O 


[ 



L ] 

O 

□ 





■ 1 

□ 

□□ □ 


1 □ □ i 

□1 

□ on □ ill* it! 

30 

i 

31 

DP 

miwt 

QH 

Finn h n rfin 

iiiiiiiiiliiiiiii Bill 

1H 

1 El El IE 

11 

1 H iH 


0 ■ 

[ 

3 Ell 

1 El El El 

IBfC 

nil 

mu 1 

1 nn n 

mm 

imf 

]Edm: 

H-T~n r3-F 

J u y IS 

0Q1B 1 
1 El El El 

—1 rzi ri.cm- 


assumed path 
of bomb 


16 


25 * 



PERSPECTIVE VIEW B 


f=~‘ | - — 

pi 

P 


§§ fi 

1 

1 1 


ry 







- -- —' 



SteilLjB' ♦ H 


Jj| ii It 


SITE PLAN 




466 





























































































































































































































































































































































































































































































t 


ROOF PLAN 
scole ° * lo 20 30 


NINTH FLOOR 




BUILD ING 

Type: Apartment building consisting of base¬ 
ment, nine upper floors and pent-house on 
roof. Construction: Reinforced concrete 
frame. Floor slabs 5" concrete. Exterior 
walls II " br i ck cav i ty . Partitions 3^" plas¬ 
ter secured to columns with £" wire 24" o.c. 
2-2 2 ” walls with I £" cavity between apartments. 
Stairway walIs 4 5 " brick. To facil itate erec¬ 
tion the reinforcing steel was prefabri¬ 
cated into "cages" and dropped into position 
between columns with additional straight bars 
being added for continuity at top and bottom 
prior to placing of concrete. 

DAMAGE 

The bomb perforated the roof and two floors 
detonating between the 7th and 8 th floors. 

Roof: Beams and columns intact. Bomb punched 
a 4'x3' hole. Slab bowed upward from blast. 
Parapet and wall of pent-house collapsed. 

9th floor: Beams and col umns intact. Approx, 
areas of damage in sq. ft. to: floor - 194; 
partitions - 900. 

8 th floor: Columns intact. 881 and 8B2 end 
connections broken, center broken up and bowed 
upward. 883 and 8B5 disintegrated. Connec¬ 
tion of 8B4 to 8 CI severed, beam sagged down 
and twisted. Connection of 8 B 6 to 8 CI broken. 
Approx, areas of damage in sq. ft. to: floor - 
830; exterior wall - 620; partitions - 1080. 

7th floor: Beams and columns most severely 
damaged. 7BI, 7B2, 7B5 and7B6 disintegrated. 
7B3 and 7B4 bent downward. 7B7 cage blown 
up. Columns 7CI and 7C2 bowed out. 7C3 broken 
and hanging from column above. Only bowed 
rods of 7C4 remain. Approx, areas of damage 
in sq. ft. to: floor - 830; exterior wall - 
1240; partitions - 3060. 

6 th floor: 6 BI collapsed. Column 6 CI dam¬ 
aged. Approx, areas of damage in sq. ft. to: 
floor - 620; exterior walls - 590; partitions 
- 1170. 

5th floor: No structural damage. Approx, 
areas of damage in sq. ft. to: floors - 120 ; 
partitions - 360; exteridr walls - 0. 

Excessive damage to beams and columns may be 
attributed in part to the use of prefabricated 
reinforcement "cages" and separate continuity 
rods. I n some cases where beams disintegrated 
the "cages" were blown out while continuity 
rods remained in place. 

Excessive column damage probably due to bond¬ 
ing partitions to columns, thereby transmit¬ 
ting forces on partitions to columns. 

Some fragmentation damage to brick walls and 
window frames occurred across the courtyard. 
Damage extended from the third to eighth floors 
being most severe at the fifth and sixth floors. 


Note Circles represent the intercept of sphere of designated 

radius with the floor in question.the center of the sphere 

being ot the estimated position of the explosion. 


April 1944 



































































































































































































































INCIDENT SUMMARY 


MULTI-STORY, REINFORCED CONCRETE FRAME 
WAREHOUSE STRUCK BY A 2200 lb. G.R BOMB 


PF * 5902/27 


(GERMAN 1000-kg.S.C. Chg.Wt.54%) 


August 1943 


° o H *1 

O « . o 

• >, o o o 

2 — O o 

2 — o o *o 


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♦I +1 


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7 • O 

3 

Q £ 

i 4 » V* 

8 

CD*- O 


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§ o J 
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o — 

W C 
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a. o — 


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V^joo 1 

\JMS-RCF 

INCIDENT ONE 

V- J 


468 






























































































































































































































































































































































INCIDENT SUMMARY 

MULTI-STORY, WALL BEARING 

SCHOOL BUILDING STRUCK BY A IIO lb. G.P BOMB 


— 



INCIDENT ONE 




PF- 5902 /28 


(GERMAN 50 K g. S.C.? Chg. Wt.50%) 




no structural damage 
to roof -- 


x t3“ hole in 
slate roofing 


3 " glazed partition de¬ 
flected z" at base , 
one pane broken by 

fragment •- 

fir. raised 4-s’in radius 
of 6 ) wood fig. dislodged 

fourth floor 


flue exposed •- 

4‘ x 6'hole in tg" brick 
wall, debris thrown 116 ' 


sash blown out 


third floor 


fir. deflected3“evenly, 
ceiling badly spalled 


/*"plaster cracks 

second floor 
SECTION A-A 


BUILDING 

Type*, Six-story (basement and four upper floors ; 
five in front). Technical College (ca. 1900) 
Construction : Walls- massive ,wel I built brick bear¬ 
ing walls. 

Floors-9-inch thick breeze concrete slabs on 5- 
inch steel filler joists, 2-inch wood block flooring. 
In this instance the fourth floor was reinforcedwith 
steel I-beams. 

Roof-slate roofing on timber trusses. 

Partitions-9-inch brick panel walls. 

DAMAGE 

Bomb perforated roof and the 13^ 2 -inch fourth floor 
slab detonating above the third floor as shown i n 
Section A-A. Structural damage was limited to the 
room (14,000 cu.ft.)in which explosion occurred and 
was confined to an area within 40 feet of the explo¬ 
sion.The bomb exploded about 5 feet from the 18- 
inch interior corridor wall. A hole 6'X4'was punched 
in this wall (probably by mass fragmentation)andthe 
debris was thrown horizontally a distance of II 6 feet 
into the Examination Hall in the center of the build¬ 
ing. An area of 250° 'was blown out of each end par¬ 
tition wall. The frontexterior bearing wall was moved 
out about /2 inch. One window sash and the corrido r 
door were blown out. The ceiling (4th.floor slab) 
within 6 feet of bomb hole was lifted and the third 
floor was deflected 3 inches uniformly by the blast 
wave. 

The I-beam above the explosion was perforated in 
web and in flange by fragments. Maximum web per- 



z- te “x 7 “J-beams 
(exposed) 


ZSO a 'of 9"brick wall 
out, steel beam over 


o 1 “ “' 10 15' 20 25* 

SCALE for Plan and Section 


zso °'of 9 "brick wall 
out, steel beam over 


PART PLAN third floor 

wood block z "■- 

sc reeding i >/z " •- 

breeze concrete 9“ -- 

filler beams 5 m X7“- - 

plaster 3/4"' - 

I-beams ig’x 7“ - - 

fragment holes -- 

FLOOR 

CONSTRUCTION atB-B 'elevation 




£ 


- * - M 

8-0 




secTTon 


foration was 4"Xl"; flange perforations wereland 
l */z inch in diameter. (See detail of floor construe — 
tion at B-B ) 

The brick fireplace was demolished ; flue exposed 
for 10 feet. A smal I fire was started in the up¬ 
holstery but was readily extinguished. The sky¬ 
light in the Area suffered heavily from debris.The 
pattern of glass damage shows how effectively 
blast is baffled by the right-angled bends in cor¬ 
ridors . 


Note Circles represent the intercept of sphere of designated 
radius with the floor in question the center of the sphere 
being ot the estimated position of the explosion. 


July 1943 













































































































































































































INCIDENT SUMMARY 


MULTI-STORY, WALL BEARING 

OFFICE BUILDING STRUCK BY A IIOO lb. G.R BOMB 



PF 5902 / 29 (GERMAN 500 kg. S.C, chg, wt. 50 %) 

BUILD ING 

Basement and f ive upper floors. Over-a11 s ize approx¬ 
imately 50 ft. by 60 ft. 


Construction: Walls - exterior brick load-bearing, 
Z2j inches thick for basement, first and second floor 
walls; 18-inch thick walls from third floor to roof. 
Internal steel frame. 

Floors and Roof - breeze concrete and filler joists. 
Shelter - basement room reinforced with 7"x6" timber 
struts and beams (set parallel with filler joists), 
some structural steel and a new 18-inch thick brick 
wa 11. 

DAMAGE 

The bomb apparently fell down the light well between 
the buildings and perforated the rear exterior wall 
and basement floor before detonating. A crater, 30 
ft. in diameter and 8 ft. deep, was formed in the 
sandy-clay soil by the explosion. The entire build¬ 
ing collapsed filling the basement and pavement at 
the front of the building with debris. A small part 
of the shelter (shown cross-hatched on the plan) did 
not collapse, however, thereby saving the lives of 
three women. They were rescued, though injured, by 
means of the emergency exit in the pavement light 
whichwas forced through at (A) . Others in the she Iter 
were killed when thrown by the blast against the base¬ 
ment wa 11 at (1) . The new I 8- i nch brick shelter wall 
was demolished. Incendiaries later started fires in 
the debr is. 

The corner building, adjacent to the one struck and 
of similar construction, suffered so severely from 
the effects of the blast and the shock that it had 
to be demolished later . However , other adjacent build¬ 
ings did not even suffer glass damage. There was no 
fragmentation damage. 



damaged.... hafr 
to be demolished 


portion 

didnot 


cross -hoTche 
of basement 
collapse 


strutted she> 
in basement 





December 1943 


470 


j 
































































































































INCIDENT SUMMARY 

MULTI-STORY, WALL BEARING 

WAREHOUSE STRUCK BY A 2200 lb. A.R BOMB 



PF 5902 /30 


(German 1000 Kg S.D. chg.wt. 14%) 




cooling 

tunnels 


four ffoors oad roof 
(torn fa |$| 4 r#tr~ " 


gangway g 


jtH,float* on, 

.40«OM;m*t: 


extent of 
debris . 


i ■ 

I -—-^ 

PLAN 1st floor assumed pgihf^ 

gangway of bomb 


gangway 


gangway^ 


3 columns 
down 








BUILD ING 

Type: Warehouse B - one of a group of three ware¬ 
houses - basement and f ive upper floors and flat roof. 
Over-all dimensions 60’xI 30 ? . 

Construct ion of Warehouse B: brick bearing walls ap¬ 
prox imately 2 ' th ick . Floors and roof 7" of concrete 
between 7" steel joists spaced at 2'x6" centers cov¬ 
ered with 2" concrete slab. F1oors and roof were sup¬ 
ported by stee 1 beams and intermediate cast iron col¬ 
umns. Basement beams and col umns encased inconcrete. 

Warehouse (C) of s imi lar constr uct i on and warehouse (A) 
is steel framed enclosed with brick walls. 

DAMAGE 

The bomb perforated the roof and 4 floors of warehouse 
(1) and exp loded on or near the f irst f loor . The major 
portion of the warehouse co llapsed to the first floor. 
The first floor collapsed into the basement in the 
area near to the bomb. 

A four story gangway connect i ng warehouses (A) and (J) , 
and part of the cooling tunnels at the fifth floor be¬ 
tween warehouses (I) and (C) col lapsed to the ground. 
The cooling tunnels were used for cooling jam as it 
passed from warehouse (6) to (D . 

The e levator shaft was stee 1 framed and rema i ned stand¬ 
ing altho considerably damaged. 

All windows inwarehouses (A) and (c) adjacent to (b) 
were blown out. 

Shelters were provided in the basements of all three 
buildings and were occupied by 1500 people when the 
bomb struck. 5 people were killed by the collapse 
of the first floor of warehouse (§) . 



January 1944 



































































































































































































































INCIDENT SUMMARY 


MULTI-STORY, WALL BEARING 
FACTORY BUILDING STRUCK BY 

PF- 5902 /3' 



1) - tttt 1 

mJ ms-wb 

A PARACHUTE MINE 

INCIDENT ONE 




Of 

oflopSed 


point of detonation 
of mine it assumed 


brick chimney te' h 
dktm.8 tee' high 
undamaged / 


entire building 
collapsed onto 
the first floor 


steel fronted 
hoisf ttwer 
undamaged 






<* * 


sms A reef 


iSmcSe 


t-otery 


hoist tower, though \ 
damaged, remained — 
standing 


reef t f 


brick wall sheared e‘A" on horizontal 
joint { also, it * out of plumb 


watt- strutted 
shelter in the 
basement 
(outlined area) 


brick wall it ' 
out of plumb 
under cores 




A origPIdg. with flat roof, built in 1896 
B- first extension with flat roof. 

C- second extension with N-tight roof 

SECTION A-A 

middle 
hoist 
tower 


chimney 


assumed pgth . / 
of para-mine 


water tonk _„• 

abt to square w 


middle 8 end hoist 
towers left standing 


1th 


fourth 


basement 


assumed path ^ j 


of para -mine 


PLAN 
scot* 

oil drawings at 


ELEVATION 


bosomont 

shelter 


u 


£=== 




-I 


showing six- story block offer the incident 


BUILDING 

Type: Six-story factory building with basement. Overall 
dimensions opprox. 75'X 240',of irregular shape. Bays 
were 16 'x 25'. 

Construction: The building wos built in three stoges of 
brick wall bearing type construction. The original build¬ 
ing, consisting of basement and three upper floors, was 
built in 18 96. The second stage consisted of the addition 
of the fourth and fifth floors and a flat roof; the third 
stage consisted of the oddition of the sixth floor with 
steel saw-tooth trusses admitting north light ■ Exterior 
brick bearing walls , 3 feet thick at the bose , and in¬ 
terior cast iron columns supported 6- inch concrete 
floors with filler joists on steel beams . The 4th and6th 
floor slabs, originally roof slabs .were 8- inch concrete 
The middle hoist tower was built in 1931 of steel frame 
and brick curtain walls. A well strutted ARP shelter 
was built in the basement. 


DAMAGE 

The parachute mine was seen by roof spotters to hit the 
building about where shown on the drawings.Examina¬ 
tion of the debris reveoled that the fifth-floor slab was 
considerably scattered about.suggesting that the mine had 
perforated the fifth and sixth floors and probably hod de¬ 
tonated below the fifth floor. The entire building, with 
the exception of the two hoist towers collopsed. The 
debris was piled evenly over the first floor, each floor 
on lop of the one originally below it with the roof tnees 
on the top. Due to the absence of earth shock and the 
absorption of the blast wave by the complete collapse of 
building , the 240- foot chimney was undamaged. Immediate¬ 
ly after the colapse , fire broke out ond burned for three 
days. 

Within a rodlus of 400 feet from the mine, roofs ond wrv 
daws of all other buildings were domaged. Some of thi s 


damage , however, wos caused by another parachute nine 
which struck a building 100 yards oway. It was reported, 
but not confirmed, that a high explosive bomb struck the 
end of the six-story building before the mine. 

Transformers and cables , housed in the end of the build¬ 
ing over the shelter, were destroyed , putting the entire 
plant out of operation until auxiliary power could be 
supplied . 

The ARP shelter, being of excellent construction wft 
strong exterior and compartment walls as welasskrdy 
overhead protection .withstood the debris load and 
saved the lives of 16 people. A smoll section, howver 
did collapse (shown cross hatched on ptonlThe remain¬ 
der of the first floor collapsed after the fire . 


4 


May 1943 











































































































GLOSSARY 


A. C. Advisory Council on Scientific Research and Develop¬ 
ment, Ministry of Supply. 

ADM. Issued to British Admiralty by Road Research Lab¬ 
oratory, Department of Scientific and Internal Research. 

ADP. Ammonium dihydrogen phosphate. 

Afterburning. The relatively slow oxidation of the products 
of the detonation of a high explosive. It may or may not 
involve atmospheric oxygen. 

Air Blast. The disturbance (shock wave) propagated through 
the air arising from a source of suddenly expanding gases 
(as from explosions, bursting diaphragms, sparks, etc.). 

AMG-NYU. Applied Mathematics Group, New York Uni¬ 
versity. 

AMP. Applied Mathematics Panel. 

AX. Ammonium nitrate. 

APC. Armor-piercing capped projectile. 

ARD. Armament Research Department (England). 

ARL/S. Admiralty Research Laboratory, Summary. 

ARM. Armament Department of Royal Aircraft Establish¬ 
ment. 

ATM. Atmosphere. 

Back Blast. The increased blast effects produced at the rear 
of a gun by a muzzle brake or blast deflector. 

Baffle (in muzzle brakes and blast deflectors). A plate which 
intercepts a fraction of the gas and deflects it away from 
the bore axis. 

Bare Charge. A charge which is not in a case. 

BHN. Brinell hardness number. Obtained by pressing steel 
ball of 10-mm diameter into the surface under a load of 
3,000 kg. The BHN is given by the load divided by the 
area of the spherical surface of the impression measured in 
square millimeters (units, kg/mm 2 ). 

Blast Deflector. A device attached to the muzzle of a gun, 
such as a muzzle brake, which intercepts and deflects a 
fraction of the blast. 

Boat-Tail. Applies to bullets. The back is not plain but 
partly beveled. 

Booster. A quantity of high explosive in which detonation 
can be more readily initiated (by means of primers) than 
can the main high-explosive filling. Boosters are used to 
initiate the main, relatively insensitive high-explosive filling. 

Bottle (in the blast of a gun). The central, bottle-shaped, 
supersonic region of a high-pressure jet bounded by sta¬ 
tionary shocks in which the main expansion of the gas 
occurs. In a gun, the neck of the bottle is in the tube. 

Brake Efficiency. The per cent of reduction in recoil energy 
produced by a muzzle brake. Brake efficiency depends on 
brake, gun, and round. 

Brinell Hardness. The Brinell method of measuring the 
surface, or superficial, hardness of a material employs a 
small hardened steel ball under a force applied for a specified 
time. The Brinell number is calculated from the dimensions 
of the resulting permanent impression. 

Brisance. The property of explosions which describes their 
shattering power, by virtue of very sudden release of energy. 
Brisance is usually measured by the depth of the dent 
produced in a steel plate by a contact explosion. 

BRL. Ballistic Research Laboratory, Aberdeen Proving 
Ground. 

Bubble Migration. The vertical motion of the gas bubble 
due to its buoyancy and the forces exerted by nearby surfaces. 

Bubble Pulse. The pressure pulse emitted by the collapse 
of the gas bubble. 

Burster Slab. A horizontal layer of concrete or masonry at 
or near the ground surface and surrounding a protective 


structure. Its purpose is to cause near-miss bombs to break 
up or to detonate prematurely. 

Cables (coaxial, electric). Electric conductors in the form of 
one or more conductors provided with insulation and an 
external conducting envelope, or shield. 

Caliber Radius. Radius of curvature of projectile’s nose 
expressed as a multiple of the projectile diameter. 

Camouflet. A cavity beneath the surface of the earth 
caused by an explosion too deep to crater. 

Cap. Protective material over the nose of the armor-piercing 
element. A cap is used to reduce deformation of the projectile 
proper. 

Case. The jacket or container of a bomb or other projectile. 
The case is usually made of steel but may also be aluminum, 
cardboard, plastic, etc. 

Cavitation. The result of negative pressures or tensions 
applied to water which pull the medium apart and form 
bubbles of gas or vapor. 

CFD. Committee on Fortification Design; originally CPPAB 
i ( q-v .)• 

Charge (high-explosive). A quantity of explosive which is 
prepared for detonation. 

Composite Rigid Projectile. A full-caliber, lightweight pro¬ 
jectile with a small armor-piercing core. 

Condenser-Microphone. A gauge which depends for its 
action upon the change in electric capacity of a condenser, 
as the plates of the condenser are deformed by the action 
of pressure. 

Countermining. The destruction of weapons by means of 
an explosion. 

CPPAB. Committee on Passive Protection against Bombing. 
This was organized by the National Research Council at 
the request of the Corps of Engineers to carry out research 
for the latter. Later called the Committee on Fortification 
Design (CFD). 

Crusher Cylinder or Sphere. L^sed in equipment for 
measuring maximum pressures in guns or underwater. The 
crusher, usually made of copper, is placed in a cylinder in 
contact with a piston that is exposed on its other side to 
the pressure being measured. The amount of compression 
given to the crusher is used as a measure of the pressure 
acting, according to a calibration previously made on 
similar specimens. 

Cup-Cone Fracture (of tensile specimen). After fracture, 
one side of the break resembles a cup with flat bottom and 
diverging sides. The other part of the break, which fits into 
the first, is a truncated cone. More complicated breaks 
can occur. 

C/W. Charge/weight ratio. 

D-2. Designation of the desensitizer in HBX explosive. 

Desensitizer. A substance which is added to an explosive to 
make it less sensitive to detonation. 

Detonation. The extremely rapid chemical reaction which 
occurs in the explosion of high explosives. Detonation is 
characterized by its propagation through the mass of 
explosives as a wave, by its great velocity, by the fact that 
it can be initiated by a shock or blow, and by the extremely 
high pressures developed. 

Detonation Velocity. The rate at which the decomposition 
zone or front travels through an explosive after it is detonated. 

Diffuser. In muzzle brake and blast deflectors, an extension 
to the muzzle or to a baffle orifice that permits the gas to 
expand and directs it towards the baffle surface. 

Diffusor. In a supersonic wind tunnel, the diverging part 
of the tunnel downstream from the working section. 



473 



474 


GLOSSARY 


DTMB. David Taylor Model Basin (U. S. Navy, Bureau of 
Ships). 

Elasticity. The property of a material whereby a stressing- 
unstressing cycle leaves no permanent deformation. The 
relation between stress and strain during the cycle is usually 
linear. See Plasticity. 

ERL. Explosives Research Laboratory, Bruceton, Pennsyl¬ 
vania (Division 8, NDRC). 

Face-Hardened Plate. Hard surface, soft back. 

Field Muzzle Attachments. Muzzle attachments compa¬ 
rable in size and weight to existing muzzle brakes. Such 
attachments may be used as field modifications on guns 
prepared to take a muzzle brake. 

Flash Charge. An explosive surrounded by a very thin layer 
of argon gas. On detonation, an intense flash of light about 
1 jusec in duration is emitted. 

Flow Stress (psi). That part of the longitudinal stress in a 
tensile specimen that is produced by the tensile force, 
corrected for the effect of the noncylindrical shape of the 
neck (if any). Therefore, this does not include the stress 
produced by any simultaneously acting hydrostatic pressure. 

Folding Skirt Projectile. A projectile for use in a tapered 
bore gun. 

Free Air. A region in the air well removed from obstacles, 
the ground, and other reflecting or absorbing surfaces 
or objects. 

Free Plate. An idealized plate target which is free to move 
without restraint when acted on by an impulsive force. 

Free Surface. The surface of the sea, i.e., the water-air 
interface. 

Gas Bubble, Gas Globe. The confined mass of gaseous 
products resulting from an underwater explosion. 

Gauge Length. In a tensile specimen, the length between 
the points to which is attached the gauge that measures the 
extension. In the hydrostatic pressure work (Chapter 16), 
the length of the uniform part of the specimen, between 
shoulders. 

GP. General purpose. 

Guillotine-Type Testing Machine. A device constructed 
at the California Institute of Technology for testing materi¬ 
als at high speeds. It consists of a pair of guide-rails between 
which slides the hammer. The hammer is attached to the 
base of the machine by heavy rubber strips. A winch raises 
the hammer against the tension of the rubber strips. 

Hardness. Resistance to distortion. Superficial hardness is 
surface hardness as measured by the Brinell or an equivalent 
method. See also BHN. 

HBX. Desensitized Torpex. 

HC. High capacity. 

HCR2. Designation for a type of plastic protection effective 
against shaped charges (Chapter 12). 

HE. High-explosive shell. 

HEAT. High-explosive antitank shell. 

High Explosive. A substance in which sudden chemical 
decomposition may be initiated by means of heat, friction, 
shocks, and blows characterized by detonation; confinement 
is not necessary to the very rapid release of energy in 
detonation. 

H.M.A./S.E.E. His Majesty’s Anti-Submarine Experimental 
Establishment at Fairlee. 

Homogeneous Plate. Uniform hardness throughout. 

HU. Harvard University. 

HVAP. High-velocity armor-piercing projectile. 

Hydrostatic Pressure (psi). A pressure uniform in all 
directions, as is produced on a body immersed in a fluid 
under pressure. 

Hypervelocity. Velocity in excess of 3,000 ft per sec. 

Isentropic. Nonconductive flow in which a fluid element 


suffers no change in entropy. Reversible adiabatic flow. 

Jacket. The soft material completely surrounding a hard 
armor-piercing core. 

Jet (from the muzzle of a gun). The muzzle blast exclusive 
of the air shock. 

Jet Separation. The separation of a jet from the walls of a 
diffuser when the forward increase in section of the diffuser 
is too abrupt. Between the separated jet and the diffuser the 
medium is stagnant and highly turbulent. 

LC. Light case. 

Lead Ratio. The ratio of the “leads,” in degrees, necessary 
for the gunner to obtain hits on the fighter in training to 
the leads necessary in combat, the fighter being at the same 
point relative to the bomber for both cases. 

Lethal Damage. The damage to a vessel sufficient to sink it 
or put it out of action. 

Limit Energy. The least energy required to perforate a plate. 

Limit Velocity. The minimum striking velocity required for 
perforation with zero remaining velocity (Navy limit). 

Line Charge. A charge, one of whose dimensions is much 
greater than the other two. 

Liner (of shaped charge). A conical, hemispherical, or other 
shaped piece of metal or glass whose convex face is backed 
by an explosive. 

Low Explosive (propellant). A substance which, once ignited, 
burns rapidly without access to air, producing gases having 
temperature and pressure depending upon confinement. 
Without confinement, the burning of low explosives is slow 
and quiet. The burning proceeds from the outer surfaces 
of the grain inward. 

Mach Number. Applies to supersonic flow of a gas. It is the 
ratio of the velocity of the gas (or of a body moving through 
it) to the local velocity of sound. See Supersonic Velocity. 

Mach Stem. The single shock wave which, under the proper 
conditions, is produced by the reflection of a shock wave 
from a surface, or by the interaction of two shock waves. 
The incident and reflected shock waves are coalesced in 
the Mach stem. 

MAE. Mean area of effectiveness. 

MC. Medium capacity. 

MRL. Maryland Research Laboratory (Division 19, NDRC). 

Muzzle Glow. A glowing of the gas near the muzzle often 
observed soon after shot ejection. This glow is due not to 
burning but to chemical changes taking place in the powder 
gas composition and, perhaps, to the incandescence of un¬ 
burned powder particles. 

NAVORD. U. S. Navy, Bureau of Ordnance. 

NDRC. National Defense Research Committee. 

Necking (of tensile specimen). During a tensile test of a 
ductile material, the load first increases, reaches a maximum, 
then decreases. During the first stage, the specimen remains 
cylindrical. At the instant of maximum load, a neck or 
local contraction first appears; this becomes more pro¬ 
nounced during the remainder of the test. 

Negative Phase (suction). The part of the shock wave in 
which the pressure is less than atmospheric. 

NG. Nitroglycerin. 

NOL. Naval Ordnance Laboratory. 

Normal Shock. A stationary shock, the front of which is 
perpendicular to the streamlines. 

Nozzle. In a supersonic wind tunnel, the converging part of 
the tunnel just upstream from the working section. 

Oblique Shock. A stationary shock, the front of which makes 
an angle, other than a right angle, with the streamlines. 

Oscillogram. The permanent record of the path of the 
cathode-ray beam on the fluorescent screen of a cathode-ray 
tube. Usually, a photographic record. 

OSRD. Office of Scientific Research and Development. 



GLOSSARY 


475 


Oxygen Balance. Complete oxygen balance requires that 
enough oxygen be combined in the original explosive so that 
on detonation every element such as carbon, nitrogen, and 
hydrogen will be completely converted to its respective oxide. 

Particle Velocity, Mass Velocity. The velocity of the 
matter in a shock wave. Usually referred to the matter 
ahead of the wave as stationary. 

Peak Pressure. The pressure in the initial part of a shock 
wave. It is usually, but not always, the highest pressure in 
the wave. 

PETX. Pentaerythritol tetranitrate. 

Piezoelectric. The property, exhibited by certain crystals, of 
generating an electric charge when subjected to pressure. 

Piezoelectricity. The electric charge produced on the faces 
of some crystals when they are strained (by the action of 
applied pressure). 

Plane Charge. A charge, two of whose dimensions are much 
greater than the third. 

Plastic Armor, Plastic Protection. The combination of 
gravel or crushed stone with pitch or bituminous binder and 
a filler such as limestone dust or wood flour. 

Plasticity. The property of a material whereby a stressing- 
unstressing cycle leaves a permanent deformation. See 
Elasticity. 

PLC. Projected line charge. 

Plume. The irregular masses of water and burnt gases 
projected into the air after a shallow underwater explosion. 

Positive Duration. The time during which the pressure in a 
shock wave is greater than that of the atmosphere. 

Positive Impulse. The integral f<f c pdt , where p is the pressure 
at the time t and t c is the positive duration of the wave, 
measured from the zero of time of the arrival of the shock 
wave at a gauge; hence, the area under the positive pressure 
part of the pressure-time curve; hence, the average pressure 
in this time, times the positive duration. 

Positive Phase. The part of the shock wave whose pressure 
is greater than that of the atmosphere. 

Primary Flash. A glowing that occurs in the high-tempera¬ 
ture region behind the normal stationary shock which 
terminates the bottle. This glow is due not to burning but 
to a resumption of the action which produces muzzle glow 
and which is inhibited when the gases enter the relatively 
cold bottle. 

Primers. Sensitive high explosives which are easily detonated 
by heat, friction, or shock; used to initiate other, less 
sensitive high explosives. 

Principle of Similitude. A law describing how the shock 
wave parameters scale. 

Propellant. See Low Explosive. 

Pursuit Curve. An idealized path in space, relative to a 
bomber, which a fighter may fly in order to obtain continued 
“hits” on the bomber. The path may be calculated if certain 
assumptions are made regarding the bomber and fighter 
velocity, the velocity of the fighter’s bullets, and the aero¬ 
dynamic behavior of the fighter along the path. 

PUS. Princeton University Station Division 2, NDRC. 

Pyroelectricity. The electric charge produced on the faces 
of some crystals when they are strained (by application 
of heat). 

“Rad” Basis. The “rad” may be defined as the angle subtended 
at the eye of the gunner by the radius of the ring in a fixed- 
ring type sight. In fixed optical sights the value of the “rad” 
in degrees depends only on the choice of ring size since the 
ring image is focused at infinity. 

Rarefaction Wave. In compressible flow, a region of low 
pressure advancing into one of high pressure. The transi¬ 
tion between the pressure levels is gradual in waves of 
rarefaction. 


Rate of Strain Effect. The rate at which a metal is deformed 
alters its strength characteristics. 

RDX. Cyclonite (cyclotrimethylenetrinitramine). 

RE. Ministry of Home Security, Research and Experiments 
Department. 

Recoil Energy. The kinetic energy of free recoil. It is the 
kinetic energy the gun tube and recoiling parts would have 
at the time the gun empties, if the motion were not impeded 
by the action of the recoil mechanism and friction on the sled. 

Residual Jet. The fraction of the muzzle blast that goes 
through the forward hole of a muzzle brake or blast deflector. 

Rest Position (of the bubble). A depth at which no migration 
of the gas bubble occurs because the buoyancy of the bubble 
is counterbalanced by a free surface repulsion or a rigid 
surface attraction. 

Reversal Angle. In muzzle brakes and blast deflectors. The 
angle in excess of 90 degrees from the bore axis at which a 
baffle plate is terminated. 

p (rho). Symbol used for density or mass per unit volume 
of a material, and equal to weight per unit volume divided 
by g , the acceleration of gravity. 

Rotary Impact Machine. A machine for testing materials 
at high speeds, usually used in tension or compression. It 
consists of a heavy wheel whose speed can be varied, a 
dynamometer whose functions are to hold one end of the 
specimen during the test and to measure the force on it, 
and a device in the wheel to be thrust out at the proper time 
to break or compress the specimen. 

RRL. Road Research Laboratory, England. 

Rupture Velocity. The velocity at which a projectile suffers 
initial failure. 

Sabot. The carrier for a subcaliber projectile. Discards on 
leaving gun. 

SAP. Semi armor-piercing. 

SBX. Slow-burning explosive. 

Scale Effect. For projectiles of a similar shape and plates 
of a given caliber thickness, the specific limit energy 
decreases with increase in projectile size. 

Scaling Laws. The laws to which the linear dimensions of an 
explosive charge or a target structure must conform in 
changing from the full scale to some smaller scale. 

Schlieren Optical System. A means of determining photo¬ 
graphically the varion of density and pressure in a moving 
gas. It depends on the fact that the refraction coefficient 
of a gas is a function of the density. 

Secondary Flash. The burning of the powder gases mixed 
with air which occurs in the turbulent shell surrounding the 
bottle. Secondary flash is the principal flash element in 
medium- and large-caliber guns. 

Selsyn Generators. The selsyn unit used in the “driver” 
position for remote control of another system. 

Shatter Energy. The energy of a projectile having a velocity 
equal to shatter velocity. 

Shatter Gap. When perforation can be obtained at velocities 
above and below but not within a certain interval, the 
interval is called a shatter gap. 

Shatter Velocity. As a velocity is increased above this 
critical value, there is a sudden change in character of hole 
made in plate and usually an abrupt increase in the energy 
required for perforation. 

Shock. A pressure discontinuity in a compressible fluid. A 
shock always advances into the low-pressure medium. 

Shock Wave. A region of compression, propagated through 
the medium (gas, liquid, or solid) in the front of which the 
pressure rise is almost infinitely steep. 

Shock Wave. In gas, a wave of increasing pressure character¬ 
ized by its very abrupt rise. Normally of finite intensity 
(not infinitesimal). 


CONFIDENTIAL 





476 


GLOSSARY 


Skirting Plate. A thin plate spaced a considerable distance 
in front of the main protective armor. 

Smoke Ring. A vortex, usually turbulent, which is produced 
ahead of an orifice through which a jet suddenly emerges. 
A turbulent smoke ring is always associated with the firing 
of a gun. 

SOG. Stanolind Oil and Gas Company, Tulsa, Oklahoma. 

Specific Limit Energy. WV 2 /d z , where W is projectile 
weight, Vi limit velocity and d projectile diameter. 

Spherical Wave. A wave originating from a point source or 
spherically shaped source whose front, as it propagates 
through the medium, is the surface of a sphere. 

Spray Dome. The cone-shaped spray of water appearing at 
the surface immediately after a shallow underwater explosion. 

SS. Scientific Section, Mine Design Department of Admiralty. 

Stability. In projectiles, relative freedom from a tendency 
to tumble or waver in flight. 

Stand Off. The distance separating target and shaped charge 
at the instant of detonation. 

Stationary Shock. A shock that does not move with respect 
to the observer. The low-pressure medium flows into 
the shock. 

Strain, Engineering. In the tensile or compressive test this 
is equal to the change of length of a short element divided 
by the original length of that element. See Strain, Natural. 

Strain-Hardening. A property of certain materials, especially 
metals, by which any deformation results in increased 
resistance to further deformation. 

Strain, Natural. This is defined by the statement that an 
increment of natural strain equals the corresponding incre¬ 
ment of change of length of a short element divided by the 
actual length of that element (not its original length). For 
small strains, natural strain and engineering strain (q.v.) 
are equal, but not for large strains. Thus 

de n = , de< ~ and e n = log e (1 + e e ) , 

1 + 

where n — natural strain and e — engineering strain. In 
simple tension or compression 


where A 0 is the initial sectional area of the specimen and 
A is the area at the instant under consideration. 

Stress, Engineering. Also called nominal or apparent stress. 
In a tensile or compressive test this is the force at any 
instant divided by the original sectional area of the specimen. 
See Stress, True. 

Stress, True. In the tensile or compressive test this is the 
force at any instant divided by the sectional area of the 
specimen at that instant. After necking in the tensile test, 
the neck area is used. See Stress, Engineering. 

Subcaliber Projectile. A projectile having a diameter smaller 
than that of the gun. 

Supersonic Velocity. The velocity, either of a gas past a 
fixed object, or of a body through a gas at rest, exceeding 
the local velocity of sound in the gas. 


SW. Interdepartmental Coordinating Committee on Shock 
Waves, Ministry of Home Security. 

Sympathetic Detonation. The detonation of an explosive 
by the impact of a nearby explosion. 

Tail (of an underwater shock wave). The later low-pressure, 
slowly decaying portion of an underwater shock wave. 

Tangent Ogive. A term describing a particular type of nose 
shape. The contour of the nose is the arc of a circle which 
is tangent to the body at the point of juncture. 

Tensile Strength (psi). In the standard tensile test of a 
material, this is the maximum load during the entire test 
divided by the cross-sectional area of the specimen. If the 
original cross-sectional area is used, the strength obtained 
is that normally specified in engineering design and is 
called engineering or apparent strength. If the actual cross- 
sectional area (reduced from the original by extension) is 
used, the value obtained is called the true strength. 

Terminal Rarefaction. The rarefaction that follows the gun 
blast caused by the over-emptying of the gun. 

Thermosetting. Having the property of acquiring strength 
when heated, usually under high pressure. 

Time Constant (of an underwater shock wave). The time 
required for the pressure in an underwater shock wave to 
fall to 1/2.718 of its peak value. 

TM. Technical memorandum. 

TNT. Trinitrotoluene. 

Tracking Rate Ratio. The ratio, at the same sight point 
relative to the bomber, of the angular rate of tracking of a 
fighter by a bomber gunner in training to the angular rate 
of tracking necessary in combat. 

Transient Jet. A jet in which the flow is variable in time but 
not periodic, such as the jet from the muzzle of a gun. 

Traveling Shock. A shock that moves with respect to the 
observer, such as a shock advancing into still air. 

Triple Point. The junction of three shock waves: incident, 
reflected, and Mach. 

Tungsten Carbide. Abbreviation for cemented or sintered 
tungsten carbide. A product of powder metallurgy which 
is composed of extremely small tungsten carbide particles 
held together by a binder such as cobalt, iron, or nickel. 
It is characterized by high density, high hardness, and 
low transverse rupture strength. 

Turbulence. The flow of a viscous fluid characterized by the 
existence of small eddies, usually with strengths and direc¬ 
tions distributed at random. 

UE. Underwater Explosions: Series of Interim Reports issued 
by the Underwater Explosives Research Laboratory at 
Woods Hole. 

UERL. Underwater Explosives Research Laboratory, Woods 
Hole Oceanographic Institution, Woods Hole, Massachu¬ 
setts (Division 2, NDRC). 

Undex. Undex series of reports issued by the Admiralty 
Undex Works, Rosyth. 

YT. Variable time. 

WA. West by air. 

WHOI. Woods Hole Oceanographic Institution, Woods Hole, 
Massachusetts. 

Working Section (of wind tunnel). The test section in which 
the model is held. 





SYMBOLS 


A 

cio 

C 

c 

D 

do 

E 

e 

/l,/2,/3,/4 

9 

}lD 

I 

K 

k 

M 

P, Pm 
Po 

Pt 

R 

S 

T 

t 

U 

u 

V 

v 

IF 

x 

Z 

X 

p 

9 


Chapter 1 

Area of piston of ball crusher gauge. 

Initial radius of a spherical charge. 

Proportionality constant (see Section 1.2.3). 
Velocity of sound in sea water. 

Depth of charge. 

Diameter of surface spray dome base. 

Energy flux corresponding to the integral 
1 / P cfP 2 dt. 

Base of natural logarithm, or 2.71S. 

Unspecified functions of the variable W%/R. 
Depth of gauge below the surface. 

Height of the spray dome above the surface. 
Shock wave impulse (or momentum) per unit area. 
Proportionality constant (see Section 1.2.6). 
Scaling factor. 

Mass. 

Peak pressure in the shock wave. 

Pressure in undisturbed medium ahead of the 
shock wave. 

Pressure at a time t behind the shock front. 
Distance from charge. 

Central identification of circular steel diaphragm. 
Period of the gas bubble oscillation. 

Time. 

Propagation velocity of the shock wave. 

Particle velocity of the water. 

Velocity of rise of the surface spray dome. 

Velocity of a target plate under explosive loading. 
Charge weight. 

Displacement of piston of ball crusher gauge. 
Depth of charge, D + 33 ft. 

Force constant. 

Density of sea water. 

Shock-wave pressure decay constant, or time 
constant. 


C 

C 

Co, c, c' 


d 

do 

E 

f, P, <t> 

h c 

kg 

H 

I 

I, Ii, h 

k 

l-l 

M 

M 

P, Pi, P 2 
Po 

Po, V, v' 

A P 
Pi 
Pr 


Chapter 2 

Charge. 

Image charge. 

Velocity of sound in front of incident shock, behind 
incident shock, and behind reflected shock 
respectively. 

Gauge-to-charge distance measured horizontally. 
Distance on ground corresponding to « extreme 
Change in energy content of the gas as it crosses 
the shock front. 

Unspecified function of the variable r/IUl cor¬ 
responding to P, I, etc., respectively. 

Height of charge. 

Height of gauge. 

Total energy liberated by an explosion. 

Incident wave h, 1 2 ' ' " In in successive stages. 
Positive impulse, psi-msec. 

Scaling factor. 

Path of triple point in Mach reflection. 

Mach shock. 

Weight of case. 

Peak pressure (gauge). 

Atmospheric pressure ( = 0) (gauge) 

Pressures (absolute) in undisturbed medium, in 
incident wave, and in reflected wave, respectively. 
Increase in pressure in enclosed rooms. 

Incident peak pressure (gauge). 

Reflected peak pressure (gauge). 


Pm 

R 

R 


S 

s 

s 

T 

t 

tc 

Ir 

U, U' 
uo, u, u' 


V 

if 


Mach peak pressure (gauge). 

Charge/weight ratio (C/IF, IF/ W c , or IF /(M 4 - IF). 

Reflected wave R\, R 2 * ’ * R n , successive stages. 

Radial distance, gauge to charge, if their heights 
are different. 

Plane-reflecting surface. 

Suction phase or negative phase. 

Slipstream. 

Triple point. 

Time. 

Crossing time or positive duration. 

Reflection time. 

Velocity of shock front propagation of incident 
and reflected shocks, respectively. 

Particle velocities in undisturbed medium, in inci¬ 
dent shock, and behind reflected shock, re¬ 
spectively. 

Volume of enclosed room. 

Wall. 


IF, 


IF, 

IF' 

W c 

y 

Z, X 
a 


a 

a extreme 
ai 

6 min 

7 


f' 

£ 

PO, P, p' 


IF 


</> 


Weights of charge (lb) for point charges; weights 
of charge per foot (lb/ft) for line charges. 

Bare charge weight equivalent to cased charge. 

Total weight of charge and its case. 

Height of Mach stem. 

Directions of air flow in reflection systems. 

Angle at which incident shock wave meets wall, or 
angle between tangent to shock and line parallel 
to wall. 

Angle at which reflected shock meets wall. 

Limiting angle of regular reflection. 

Angle of incidence for which £' has the value for 
head-on reflection. 

Angle of incidence for which U is a minimum. 

Ratio of specific heats at constant pressure and 
volume (7 = 1.40 for air at moderate temper¬ 
atures). 

p'/p, compression ratio in reflected shock. 

po/p, inverse of compression ratio in incident shock. 

Densities in front of incident shock, behind incident 
shock, and behind reflected shock, respectively. 

Angle determined by the triple point T, the point 
on the wall at which the triple point leaves the 
wall do, and the wall IF. The half-angle of the 
Mach F. 


A 

a 


a g 

B 

C 

c 

D 

d 

E 

E' 

E" 

F 


Chapter 3 

Scale factor (general). 

Acceleration; also thickness of front wall of under¬ 
ground structure (in.). 

Acceleration in units of g (gravity) [equation (15)]. 

Numerical constant associated with particle veloc¬ 
ity and of order 0.7 [equation (10)]. 

Depth factor for cratering. 

Total crack width in front face of target (in.) 
[equations (25) and (28)]. 

Displacement (ft) [equations (17), (18), (19), (20), 

( 2 !)]. 

Depth of charge in earth (ft); also, diameter of 
reinforcing bars in structure (in). 

Energy; also, explosive factor for peak pressure 
(Tables 4, 9, and 10). 

Explosive factor for impulse (Tables 6 , 9, and 10). 

Explosive factor for cratering (Tables 8 , 9, and 10). 

Force; also, coupling factor for peak pressure and 
impulse [equations ( 2 ) and ( 6 )]. 


fcONFIDENTIAL 


477 




478 


SYMBOLS 


g The acceleration of gravity, 384 in. /sec 2 . 

H Vertical dimension of target wall (in.). 

h (subscript) Horizontal. 

I Impulse per unit area, usually in free earth (psi-sec) 

[equations ( 6 ), (7), ( 6 '), (7')]. 

1' Total impulse on target wall. 

A’ Soil constant for pressure and for seismic waves, 

related to k' and k" (psi) (Table 5). 

A-' Soil constant for impulse = 5.5 4 /pk (Table 7). 

k" Soil constant for cratering = 1.3A; 12 . 

L Length; also, horizontal dimension of target wall 

(in.). 

M Mass. 

K Number of reinforcing bars that are stretched by 

bending of target wall. 

?i An exponent. 

P Pressure; in particular, peak pressure (psi) [equa¬ 

tions (2) and (3)]. 

p Pressure; usually less than peak pressure (psi). 

Q Participation factor for damage to target wall 

[equation (28)]. 

R Crater radius in earth (ft) [equation (22)]. 

r Distance from charge (ft), see X; (subscript) 

reflected. 

S Length scale factor; also, strength factor of target 

[equation (25)]. 

T Time; scabbing limit thickness of target wall for 

earth-backed contact explosion [equation (27)]. 
v Maximum particle velocity (in./sec) [equation (10)]. 

r Seismic velocity (fps); velocity of any part of 

pressure wave; (subscript) vertical. 

TL Weight of explosive charge (lb). 

x ( Maximum center deflection of wall of structure (in.). 

8 Strain in a medium. 

X Dimensionless unit of distance from charge = r/W I 

p Density of earth, or weight per cubic inch divided 


by g in inches per second, approximately 0.00015. 

Pc Density of concrete, in same units as p, approx¬ 

imately 0 . 00022 . 

cr Average yielding strength of reinforcing steel in 

structure (numerically between ordinary yield 
strength and ultimate strength), (psi), normally 
of the order 60,000. 

Chapter 6 

C Ballistic coefficient for determination of velocity 

losses in flight. 

C de Marre terminal ballistic coefficient employed by 

British Ordnance Department. 

e Energy of projectile. 

e? Energy of full-caliber projectile. 

es Energy of subcaliber projectile. 

d Projectile diameter (ft.) 

E(x) Ratio of striking energies of two projectiles at 

range x. 

F Thompson terminal ballistic coefficient employed 

by V. S. Navy. 

E(.r) Fractional energy retained at range x. 

k de Marre terminal ballistic coefficient employed 

by V. S. Army. 

K Drag coefficient. 

M Total mass of projectile. 

Ms Mass of subprojectile. 

Me Mass of carrier. 

Mf Mass of full-caliber projectile. 

R Ratio of diameter of subprojectile to that of gun. 

t Plate thickness (ft). 

Vi Limit velocity (fps). 

Fo Muzzle velocity. 

TF Projectile weight (lb). 

6 Angle of incidence, i.e., angle between trajectory 

and normal to face of plate. 




BIBLIOGRAPHY 


Numbers such as Div. S-100-M1 indicate that the document listed has been microfilmed and that its title appears in 
the microfilm index printed in a separate volume. For access to the index volume and to the microfilm, consult the 
Army or Navy agency listed on the reverse of the half-title page. 


Chapter 1 

1. List of Titles of Undex Papers 1 to 1 IS, with New Security 
Classifications, Admiralty Undex Panel and Subpanel, 
December 1944. 

2. Introduction to Explosives, George B. Kistiakowsky, 

OSRD 5401, OEMsr-202, Service Projects OD-01, OD- 
04, and NO-290, Carnegie Institute of Technology. 
Aug. 2, 1945. Div. 8-100-MI 

3. Calculation of Detonation Pressures of Several Explosives, 

Stuart R. Brinkley, Jr. and E. Bright Wilson, Jr., 
OSRD 1231, NDCrc-168, Service Projects OD -02 and 
NO-144, HU, Mar. 1, 1943. Div. S-500-M1 

4. Calculation of the Detonation Properties of Some Service 

Explosives, Stuart R. Brinkley, Jr., and E. Bright Wilson, 
Jr., OSRD 1510, NDCrc 168, Service Projects OD -02 
and NO-144, HU, June 14, 1943. Div. 8-502-M2 

5. Underwater Explosives and Explosions, Interim Report, 

UE-4, NDRC Division 8 , UERL, Nov. 15-Dec. 15, 
1942, pp. 1-2. Div. 2-130-MI 

6 . Underwater Explosives and Explosions, OSRD 4874, 

Interim Report UE-32, NDRC Division 2, UERL, 
Mar. 15-Apr. 15. 1945, pp. 16-36. Div. 2-130-MI 

7. Underwater Explosives and Explosions, Interim Report 

UE-19, NDRC Division 8 , L T ERL, Feb. 15-Mar. 15, 
1944, pp. 9-10. Div. 2-130-MI 

8 . Oblique Reflection of Shocks, John von Neumann, Ex¬ 
plosive Research Report 12, NAVORD, October 1943. 

9. Interaction of Shock and Rarefaction Waves in One- 

Dimensional Motion - Richard Courant and Kurt O. 
Friedrichs, OSRD 1567, OEMsr-944, Service Projects 
OD-03 and NO-144, AMG-NYU, 38.1, NDRC Division 
8 , AMP, July 5, 1943. AMP-101.1-M4 

10. The Interaction of Shock Waves, R. W. Wood, OSRD 1996, 
OEMsr-773, Service Projects AN -1 and OD-30, Johns 
Hopkins University, Nov. 4, 1943. Div. 2-120-M4 

11. Regular Reflection oj Shocks in Ideal Gases, H. Polacheck 
and R. J. Seeger, Explosives Research Report 13, 
NAVORD, February 1944. 

12. Interaction of Shock Waves in Water-Like Substances, 
H. Polachek and R. J. Seeger, Explosives Research 
Report 14, NAVORD, August 1944. 

13. Photography of Underwater Explosions, Paul M. Fye, 
Ralph W. Spitzer, and John E. Eldridge, OSRD 6246, 
NDRC A-368. 

14. Underwater Explosives and Explosions, Interim Report 

L"E- 21 , NDRC Division 8 , UERL, Apr. 15-May 15, 
1944, pp. 52-65. Div. 2-130-MI 

15. Diaphragm Gauge Studies of Underwater Explosions, 
John E. Eldridge, OSRD 6248, NDRC A-370. 

16a. Underwater Explosives and Explosions, OSRD 4810, 
Interim Report UE-30, NDRC Division 2, UERL, 
Jan. 15-Feb. 15, 1945, pp. 20-31. Div. 2-130-MI 

b. Ibid., pp. 32-37. 

17. Theory of the Pulsations of the Gas Bubble Produced by an 

Underwater Explosion, Conyers Herring, OSRD 236, 
NDRC C4-sr20-010, Columbia University Division of 
War Research, October 1941. Div. 6-510.12-MI 

18. Vertical Motion of a Spherical Bubble and the Pressure 
Surrounding It, G. I. Taylor, OSRD Liaison Office 


II-5-2702, Report SW.19, Aug. 4, 1942. Div. 6-540.2-M2 

19. Radial Motion of Water Surrounding a Sphere of Gas in 

Relation to Pressure Waves, E. H. Kennard, Report 517, 
DTMB, September 1943. Div. 6-510.23-M9 

20. Critical Survey of Bubble Phenomena Based on Informa¬ 
tion Available up to August 1943, H. N. V. Temperley, 
Undex 64, AUE/TRI. 15/RF. 3, Admiralty Undex Works, 
Rosyth, November 1943. 

21. On the Best Location of a Mine Near the Sea Bed. Max 
Shiftman and Bernard Friedman, [OEMsr-945,] Report 
37.1R, AMG-NYU 49, AMP, May 1944. AMP-407-M1 

22 . Migration of Underwater Gas Globes Due to Gravity and 

Neighboring Surfaces, E. H. Kennard, Report R-182, 
DTMB, December 1943. Div. 6-510.23-M10 

23. Motions of a Pulsating Gas Globe Under Water ; Photo¬ 
graphic Study, D. C. Campbell and C. W. Wyckoff, 
Report 512, DTMB, May 1943. 

24. Small-Scale Underwater Explosions Under Reduced At¬ 
mospheric Pressure, D. C. Campbell and C. W. Wyckoff, 
Report 520, DTMB, November 1943. 

25. The Oscillation of the Gas Bubble Formed by a Detonator 
Exploding Under Water: Detailed Comparison of Theory 
with Experiment, H. N. V. Temperley, Undex 83, 
AUW/TRI.73/RP.13, Admiralty Undex Works, Rosyth, 
March 1944. 

26. Note on the “Second Pulse ” Effect for Large Charges, 
OSRD Liaison Office WA-556-33, SS Report 1179, 
Mine Design Department, Great Britain, Feb. 17, 1943. 

Div. 6-510.23-M15 

27. The Experimental Evidence on the Behavior of the Gas 
Bubble Due to the Explosion of a Aik VII Depth Charge, 
SS Informal Report 1944, Undex 73, Mine Design 
Department, Great Britain, September 1943. 

28. Measurement of Bubble Pulse Phenomena. I Mark 6 
Depth Charges TNT Loaded, C. P. Slichter, W. G. 
Schneider, and R. H. Cole, OSRD 6242, NDRC A-364. 

29. Measurement of Bubble Pulse Phenomena. II Small 
Charges, A. B. Arons, A. Borden, and B. Stiller, OSRD 
6578, NDRC A-470. 

30. Underwater Explosions Near the Sea-Bed, H. F. Willis 
and M. I. Willis, Internal Report 142, Undex 52, 
H.M.A./S.E.E., Sept, 9, 1943. 

31. The Movement of the Explosion Bubble Produced by 1-Oz. 
Charge of Polar Ammon Gelignite Detonated Underwater 
in the Road Research Laboratory Tank, Undex 78, ADM- 
162, RRL, February 1944. 

32. Vertical Displacement of the Gas Bubble Formed by an 
Underwater Explosion, H. F. Willis and P. T. Ackroyd, 
Internal Report 128, Undex 36, H.M.A./S.E.E., Fair- 
lie, May 8 , 1943. 

33. Damage to Thin Steel Cylindrical Shells by Underwater 
Explosions, J. C. Decius and Paul M. Fye, OSRD 6247, 
NDRC A-369. 

34. Underwater Explosives and Explosions, Interim Report 

UE-16, NDRC Division 8 , UERL, Nov. 15-Dec. 15, 
1943, pp. 34-39. Div. 2-130-MI 

35. Underwater Explosives and Explosions, OSRD 4671, 

Interim Report UE-29, NDRC Division 2, UERL, 
Dec. 15, 1944-Jan. 15, 1945. Div. 2-130-MI 

36. Underwater Craters Formed by Explosions on the Sea 


CONFIDENT! AT. 


479 




480 


BIBLIOGRAPHY 


Floor, John E. Eldridge, Paul M. Fye and others, 
OSRD 6244, NDRC A-366, OEMsr-569, Service Project 
NO-263, WHOI, January 1946. Div. 2-132-M3 

37. Measurement of Pressure on the Sea Bed Resulting from 

Surface Waves Created by Underwater Explosions , Ralph 
W. Spitzer, OSRD 6245, NDRC A-367, OEMsr-569 and 
NOrd-9500, Service Project NO-262, WHOI, March 
1946. Div. 2-131-M6 

38. Surface Waves Produced by Firing Underwater 32-lb. 
Charges of Polar Ammon Gelignite at Various Depths, 
Undex 122, ADM 223, RRL, February 1945. 

39. Memorandum on the Generation of Surface Waves by an 
Underwater Explosion, John G. Kirkwood, Undex 94, 
August 1944. 

40. Surface Waves from an Underwater Explosion, G. Hart¬ 
man, John G. Kirkwood, and R. J. Seeger, report to be 
published by NAVORD. 

41. Surface Waves in Water of Variable Depths, AMG-NYU 
143, AMP. 

42. Production of Surface Waves by Underwater Explosions, 
Ralph W. Spitzer and Abraham M. Shanes, OSRD 4259- 
A, Interim Report Secret Supplement UE-26 SS, NDRC 
Division 2, UERL, Sept. 15-Oct. 16, 1944. Div. 2-130-MI 

43. Production of Surface Waves by Underwater Explosions. 

II. Comparison of Distributed and Lumped 1,800-Lb. 
Charges, Ralph W. Spitzer, OSRD 4259-A, Interim 
Report Secret Supplement, UE-27 SS, NDRC Division 
2, UERL, Nov. 15, 1944. Div. 2-130-MI 

44. The Measurement of Underwater Explosions for Service 
Weapons at UERL, j. S. Cole, OSRD 6240, NDRC A-362. 

45. Summary of Underwater Explosive Measurements, J. S. 
Cole, OSRD 6241, NDRC A-363. 

46. Measurement of Underwater Explosion Pressures (to Apr. 
1, 194-2) Part /, E. Bright Wilson, Jr. and R. H. Cole, 
OSRD 523, OEMsr-202, Service Project OD-03, Report 
226, Carnegie Institute of Technology, Apr. 24, 1942. 

Div. 2-131-M2 

47. Measurement of Underwater Explosion Pressures (to July 
1, 1942) Part II, E. Bright Wilson, Jr., OSRD 753, 
OEMsr- 202 , Service Project OD-03, Report 301, 
Carnegie Institute of Technology, July 21 , 1942. 

Div. 2-131-M3 

48. Trials of Mark VI and Mark IX Depth Charges Loaded 

with TNT and with Baronal, OSRD 1220, OEMsr-569, 
Service Projects OD-04 and NO-138, NDRC Division 
8 , UERL, WHOI, Feb. 22, 1943. Div. 2-133-MI 

49. Underwater Explosives and Explosions, Section B-l, 

Interim Report UE-1, Division 8 , UERL, Aug. 15- 
Sept. 15, 1942, pp. la-3. Div. 2-130-MI 

50. Underwater Explosives and Explosions, Interim Report 

UE-9, NDRC Division 8 , UERL, Apr. 15-May 15, 1943, 
pp. 13-23. Div. 2-130-MI 

51. Underwater Explosives and Explosions, OSRD 5161, 

Interim Report LE-34, NDRC Division 2, UERL, 
May 15-June 15, 1945, pp. 2-24. Div. 2-130-MI 

52. Underwater Efficiency of Aluminized Explosives, Summary 
M. S. 940/42, AC 3338, WA, Phys./Ex. 372, Mine 
Design Department, Great Britain. Oct. 22 , 1942. 

53. Design of Experiments, R. A. Fisher, Oliver, and Boyd, 
Edinburgh, Scotland, 1935. 

54. The Planning of Experiments Requiring Statistical Inter¬ 
pretation, E. Bright Wilson, Jr., Technical Memorandum 
6 , UERL, Oct. 2, 1944. 

55. Underwater Explosives and Explosions, Interim Report 

UE-22, NDRC Division 2, UERL, May 15-June 15, 
1944, pp. 30-32. Div. 2-130-MI 

56. Hugoniot Calculation for Sea Water at the Shock Front, 
A. B. Arons, and R. R. Halverson, OSRD 6577, NDRC 


A-469, OEMsr-569 and NOrd-9500, Service Project 
NO-223, WHOI, March 1946. Div. 2-131-M7 

57. Depth of Explosion of Aerial Depth Bombs with Some 
Data on Bomb Trajectories, R. R. Halverson and W. G. 
Schneider, OSRD 6258, NDRC A-380. 

58. Determination of Depth of Explosion of Statically-Fired 
Depth Bombs from Photographs of the Dome Spray, 
Chaim L. Pekeris, NDRC Section 6.1, June 1944. 

59. Splashes from Underwater Explosions: Part I. Shallow 
Charges, H. Kolsky, M. T. Sampson, Chester I. Snow, 
and A. C. Shearman, Undex 118, December 1944. 

60. Underwater Explosives and Explosions, OSRD 4406, 

Interim Report UE-27, Division 2 , LERL, Oct. 15- 
Nov. 15, 1944, pp. 19-21. Div. 2-130-MI 

61. Design and Use of Tourmaline Gauges for Piezoelectric 
Measurement of Underwater Explosion Pressures, A. B. 
Arons and R. H. Cole, OSRD 6239, NDRC A-361. 

62. The Pressure Wave Produced by an Underwater Explosion, 
III (to August 15, 1942), John G. Kirkwood and John M. 
Richardson, OSRD 813, OEMsr-121, Service Project 
OD-03, Report 326, Cornell University, Aug. 24, 1942. 

Div. 2-131-M4 

63. Calibration of Stanolind Oil and Gas Company Tourmaline 

Gauges, Eginhard Dietze, OSRD 6 .1-srl 130-1971, NS- 
139, Underwater Sound Reference Laboratories, Oct. 31, 
1944. Div. 6-554.3-M44 

64a .Journal de VEcole Polytechnique, Hugoniot, Paris, Vol. 
57, 1887, p. 3. 
b. Ibid., Vol. 58, 1888, p. 1. 

65. Theory of Shock Waves (to August 31, 1942), John von 

Neumann, OSRD 1140, OEMsr-218, Service Projects 
OD -02 and OD-03, Institute for Advanced Study, 
January 1943. Div. 2-120-M2 

66 . Plane Shock Waves, George B. Kistiakowsky and E. 

Bright Wilson, Jr., OSRD 70, NDCrc-35, Service 
Projects OD -02 and OD-03, Progress Report 7, NDRC 
Division 8 , HU, Jan. 17, 1941. Div. 2-120-MI 

67. The Hydrodynamic Theory of Detonation and Shock Waves 

(to June 30, 1941), George B. Kistiakowsky and E. 
Bright Wilson, Jr., OSRD 114, NDCrc-30, Service 
Projects OD-02 and OD-03, Final Report 52, NDRC 
Division 8 , HU, Aug. 15, 1941. Div. 2-131-MI 

68 . Pressure-Time Curves for Submarine Explosions, Paper II, 
W. G. Penney and H. K. Dasgupta, OSRD Liaison 
Office II-5-2143, SW 20, RC 333, July 23, 1942. 

69. Comments on the Current Theories of the Pressure Pulse 
of Submarine Explosions, W. G. Penney, Undex 72, 
December 1943. 

70. The Spherical Detonation Wave in TNT and TNT/RDX 
Mixtures, H. K. Dasgupta and W. G. Penney, AC-3733, 
November 1944. 

71. The Theory of Shock Waves for an Arbitrary Equation 
of State, H. A. Bethe, OSRD 545, May 1942. 

72. The Pressure Wave Produced by an Underwater Explosion 
(to May 15, 1942), John G. Kirkwood and H. A. Bethe, 
OSRD 588, May 1942. 

73. The Pressure Wave Produced by an Underwater Explosion, 
John G. Kirkwood and E. W. Montroll, OSRD 670, 
Serial No. 281, Division B, to July 1, 1942. 

74. The Pressure Wave Produced by an Underwater Explosion, 
II, John G. Kirkwood and E. W. Montroll, OSRD 
676, July 1942. 

75. The Pressure Wave Produced by an Underwater Explosion, 

IV, John G. Kirkwood, E. W. Montroll, and John M. 
Richardson, OSRD 1030, November 1942. 

76. The Pressure Wave Produced by an Underwater Explosion, 

V, John G. Kirkwood, Stuart R. Brinkley, Jr., and John 
M. Richardson, OSRD 2022, November 1943. 



BIBLIOGRAPHY 


481 


77. The Pressure Wave Produced by an Underwater Explosion, 

VI, The Cases of Cylindrical Symmetry, Oscar K. Rice 
and R. Grinell, OSRD 2023, November 1943. 

78. The Pressure Wave Produced by an Underwater Explosion, 

VII, John G. Kirkwood, OSRD 3949, July 1944. 

79. The Pressure Wave Produced by an Underwater Explosion, 

VIII, The Case of Cylindrical Symmetry, II, Oscar K. 
Rice and R. Grinell, OSRD 3950, July 1944. 

SO. Underwater Explosives and Explosions, Interim Report 
UE- 8 , NDRC Division 8 , UERL, Mar. 15-Apr. 15, 
1943, pp. 3-10. 

81. Underwater Explosives and Explosions, Interim Report 
UE-24, NDRC Division 2, UERL, July 15-Aug. 15, 1944, 

pp. 2-6. 

S2. Theory of the Propagation of Shock Waves from Explosive 
Sources in Air and Water, John G. Kirkwood and 
Stuart R. Brinkley, Jr., OSRD 4814, NDRC A-318, 
OEMsr-121, Service Projects OD-03 and NO-224, 
Cornell University, March 1945. Div. 2-120-M6 

83. Tables and Graphs of the Theoretical Peak Pressures, 

Energies, and Impulses of Shock Waves from Explosive 
Sources in Sea Water, Stuart R. Brinkley, Jr. and John 
G. Kirkwood, OSRD 5649, NDRC A-342, OEMsr-121, 
Service Projects OD-03 and NO-224, Cornell University, 
October 1945. Div. 2-131-M5 

84. The Plastic Deformation of Circular Diaphragms under 
Dynamic Loading by an Underwater Explosion Wave. 
John G. Kirkwood and John M. Richardson, OSRD 
4200, OEMsr-121, Service Projects OD-03 and NO-224, 
NDRC Division 8 , Cornell University, Sept. 30, 1944. 

Div. 2-431.22-M6 

85. Underwater Explosives and Explosions, Interim Report 

UE-18, NDRC Division 8 , UERL, Jan. 15-Feb. 15, 1944, 
pp. 10-14. Div. 2-130-MI 

86 . Effectiveness of Near Miss Bombs against Warships, 
E. Bright Wilson, Jr., Report TM-1, NDRC Division 2, 
UERL, June 23, 1944. 

87. Uriderwater Explosives and Explosions, Section B-l, 

Interim Report UE-2, NDRC Division 8 , UERL, 
Sept. 15-Oct. 15, 1942, pp. 1-7. Div. 2-130-MI 

88 . Underwater Explosives and Explosions, Section B-l, 

Interim Report UE-3, NDRC Division 8 , UERL, 
Oct. 15-Nov. 15, 1942, pp. 2-3. Div. 2-130-MI 

89. Underwater Explosives arid Explosions, Interim Report 

UE- 6 , NDRC Division 8 , UERL, Jan. 15-Feb. 15, 1943, 
pp. 4-8. Div. 2-130-MI 

90. Underwater Explosives and Explosions, Interim Report 

UE-7, NDRC Division 8 , UERL, Feb. 15-Mar. 15, 1943, 
pp. 19-20. Div. 2-130-MI 

Ola. Underwater Explosives and Explosions, Interim Report 
UE-15, NDRC Division 8 , LlERL, Oct, 15-Nov. 15, 1943, 
p. 13. Div. 2-130-MI 

b. Ibid., p. 18. 

92. The Plastic Deformation of Marine Structures by an 
Underwater Explosion, John G. Kirkwood, OSRD 788, 
OEMsr-121, Service Project OD-03, Report 308, NDRC 
Division 8 , Cornell University, Aug. 11, 1942. 

Div. 2-132-MI 

93. The Plastic Deformation of Marine Structures by an 

Underwater Explosion Ware, II, John G. Kirkwood, 
OSRD 1115, OEMsr-121, Service Projects OD-02 and 
OD-03, Report 450, NDRC Division 8 , Cornell Univer¬ 
sity, Dec. 9, 1942. Div. 2-132-M2 

94. Theory of the Plastic Deformation of Thin Plates with 
Applications, John M. Richardson, OSRD 5660, NDRC 
A-344, OEMsr-121, Service Projects OD-03, NO-233, 
and others, Cornell University, October 1945. 

Div. 2-431.1-M2 


95. The Distortion Under Pressure of a Diaphragm Which Is 
Clamped Along Its Edge and Stressed Beyond the Plastic 
Limit, G. I. Taylor, OSRD Liaison Office, II-5-2799, 
Report SW. 24, Sept. 1, 1942. 

96. Underwater Explosives and Explosions, Interim Report 

UE-5, NDRC Division 8 , UERL, Dec. 15, 1942-Jan. 15, 
1943, pp. 2-6. Div. 2-130-MI 

97. Underwater Explosives and Explosions, Interim Report 

UE-14, NDRC Division 8 , UERL, Sept. 15-Oct. 15, 
1943, pp. 8-9. Div. 2-130-MI 

98. Underwater Explosives and Explosions, Interim Report 

UE-12, NDRC Division 8 , UERL, July 15-Aug. 15, 
1943, p. 11. Div. 2-130-MI 

99. Experiments with 1 /76th Scale Model of Explosions near 
Y 2 Scale Asset Target, G. I. Taylor and R. H. Davies, 
Undex 21, March 1943. 

100. The Attack by Explosive Charges of a 1/11.25 Scale Asset 
Target, Undex 30, ADM/118/ARD, May 1943. 

101. Damage to Submerged Submarines by Underwater Explo¬ 
sions, A. H. A. Hogg, Undex 56, AUW/TRI.12/RF.2, 
Admiralty Undex Works, Rosyth, October 1943. 

102. Scale Relationships in 1 /11.25-, x /r, and Full-Scale Asset 
Trials, Undex 97, ADM/191, RRL, July 1944. 

103. Dimensional Analysis, Percey W. Bridgman, Yale 
University Press, 1931. 

104. The Speed Effect in Copper Crusher Cylinders and Copper 
Spheres, Frederick Seitz, Jr., Andrew W. Lawson, and 
Park H. Miller, Jr., OSRD 619, NDRC A-63, OEMsr- 
132, Service Projects OD-34, CE-5, and others, Uni¬ 
versity of Pennsylvania, June 1942. Div. 2-431.21-MI 

105. Underwater Explosives and Explosions, OSRD 5417, In¬ 

terim Report UE-35, NDRC Division 2, UERL, June 
15-July 15, 1945, pp. 2-27. Div. 2-130-MI 

106. Buckling Instability of Thin Cylindrical Shells Under 
External Static Loading, John G. Kirkwood, John M. 
Richardson, and Elaine M. Frankel, OSRD 3780, 
OEMsr-121, Service Project NO-224, NDRC Division 8 , 
Cornell University, June 15, 1944. Div. 2-431.22-M5 

107. Buckling Instability of Cylindrical Shells under Dynamic 
Loading, John G. Kirkwood and John M. Richardson, 
OSRD 4698, NDRC A-316, OEMsr-121, Service Projects 
OD-03 and NO-224, Cornell University, February 1945. 

Div. 2-431.22-M7 

108. Countermining of Japanese A nti-Boat Mines (JE and JG ) 

by Underwater Explosions, Paul M. Fye, John E. 
Eldridge, and others, OSRD 6243, NDRC A-365, 
OEMsr-569, Service Project NO-223, WHOI, November 
1945. Div. 2-133-M2 

109. Underwater Explosives and Explosions, Interim Report 

UE-17, NDRC Division 8 , UERL, Dec. 15, 1943- 
Jan. 15, 1944, pp. 16-19. Div. 2-130-MI 

110. Nature of the Pressure Impulse Produced by the Detonation 
of Explosives under Water. An Investigation by the 
Piezoelectric Cathode Ray Oscillograph Method. Part A. 
Methods and Apparatus. Part B. Experimental Results. 
British Report ARLS/S/12 C. B. 01670 (12), ARL, 
pp. 442-616. 

111. Construction of Tourmaline Gauges for Piezoelectric 
Measurement of Explosion Pressures, Clifford Frendel, 
OSRD 6256, ‘ NDRC A-378, OEMsr-569, Service 
Projects OD-03 and NO-223, WHOI, January 1946. 

Div. 2-11 IT 1-MS 

112. Design and Use of Tourmaline Gauges for Piezoelectric 
Measurements of Air Blast, A. B. Arons and C. W. Tait, 
OSRD 6250, NDRC A-372. 

113. Instrumentation for the Measurement of Underwater 
Explosion Pressures, M. A. Greenfield and M. M. 
Shapiro, Report 523, DTMB, September 1944. 


COX FIDENTT A W 






482 


BIBLIOGRAPHY 


114. Electrical Instruments for Study of Underwater Explosions 

and Other Transient Phenomena, R. H. Cole, David 
Stacey, and R. M. Brown, OSRD 6238, NDRC A-360, 
OEMsr-569, Service Projects NO-223 and OD-03, WHOI, 
December 1945. Div. 2-131.1-M2 

115. A Tourmaline Crystal Gauge for Underwater Explosion 
Pressure, A. R. Cohen and B. Stiller, Report It-157, 
DTMB, December 1943. 

116. The Use of Electrical Cables with Piezoelectric Gauges, 
R. H. Cole, OSRD 4561, NDRC A-306, OEMsr-569, 
Service Project NO-223, WHOI, January 1944. 

Div. 2-111.11-M4 

117. Consistency of the NOL Ball Crusher Gauge, R. H. Brown, 
Explosives Report 1, NAVORD, February 1944. 

118. High Speed Compression Testing of Copper Crusher 

Cylinders and Spheres, O. C. Simpson, E. L. Fireman, 
and James S. Koehler, OSRD 3330, NDRC A-257, 
OEMsr-825, Projects OD-57, NO-7, and P2-301, 

Carnegie Institute of Technology, March 1944. 

Div. 2-431.21-M2 

119. High Speed Compression Testing of Copper Crusher Cylin¬ 

ders and Spheres: Part II, G. H. Winslow, and W. II. 
Bessey, OSRD 5039, NDRC A-324, OEMsr-825, Service 
Projects OD-57, NO-7, and NS-109, Carnegie Institute 
of Technology, April 1945. Div. 2-431.21-M3 

120. Underwater Explosives and Explosions, Interim Report 

UE-13, NDRC Division 8 , UERL, Aug. 15-Sept. 15, 
1943, pp. 11-12. Div. 2-130-MI 

121. Theory of Crusher Gauges, G. K. Hartman, Memoran¬ 
dum for File A16 (CND) (Re 6 b), NAVORD, Sept. 25, 

1942, 

122. An Iterative Method for Calculating the Calibration Curve 
for a Crusher Gauge, R. M. Brown, Explosives Research 
Memorandum 6 , NAVORD, Apr. 3, 1944. 

123. Underwater Explosives and Explosions, Interim Report 
UE-10, NDRC Division 8 , UERL, May 15-June 15, 

1943, pp. 21-22. Div. 2-130-MI 

124. Underwater Explosives and Explosions, OSRD 6116, 

Interim Report UE-37, NDRC Division 2, L^ERL, 
Aug. 15-Sept. 15, 1945. Div. 2-130-MI 

125. Underwater Explosives and Explosions, OSRD 4259, 

Interim Report UE-26, NDRC Division 2, UERL, 
Sept, 15-Oct. 15, 1944, pp. 8-10. Div. 2-130-MI 

126. Underwater Explosives and Explosions, Interim Report 
UE-20, NDRC Division 8 , UERL, Mar. 15-Apr. 15, 

1944, pp. 45-47. Div. 2-130-MI 

127. The Modugno Gauge (Its Construction, Use, and Typical 
Results), Underwater Explosion Report 1942-3, Navy 
Department, Bureau of Ships, October 1942. 

128. Underwater Explosives Research, Duncan P. MacDougall, 

OSRD 1035, OEMsr-202, Report 429, Service Projects 
OD-03 and OD-04, NDRC Division 8 , Carnegie Institute 
of Technology, Nov. 18, 1942. Div. 2-131.1-MI 

129. Experiments on the Pressure Wave Thrown out by Sub¬ 
marine Explosions, H. W. Hilliar, R. E. 142/19, Decem¬ 
ber 1919. 

130. The Hilliar Gage, G. K. Hartman, Confidential Report 
531, DTMB. 

131. Underwater Explosives and Explosions, Interim Report 

UE-11, NDRC Division 8 , UERL, June 15-July 15, 
1943, pp. 12-14. Div. 2-130-M1 

132. Underwater Explosives and Explosions, Interim Report 

UE-23, NDRC Division 2, UERL, June 15-July 15, 1944, 
pp. 2-11. Div. 2-130-MI 

133. Underwater Explosives and Explosions, OSRD 4S73, 

Interim Report UE-31, NDRC Division 2, UERL, 
Feb. 15-Mar. 15, 1945, pp. 2-21. Div. 2-130-MI 


134. Hydrodynamics, Horace Lamb, Cambridge University 
Press, 1932, Chapter IX, p. 363. 

135. Photographs of Surface Phenomena Following Explosion 
of Mark of Aircraft Depth Bombs Fired at Various Depths, 
Report TM- 11 , NDRC Division 2, UERL, June 27, 1945. 

136. Underwater Explosives and Explosions, OSRD 4149, 

Interim Report, UE-25, NDRC Division 2 , UERL, 
Aug. 15-Sept. 15, 1944, pp. 35-40. Div. 2-130-MI 

137. Underwater Explosives and Explosions, OSRD 4407, 

Interim Report UE-28, NDRC Division 2, UERL, 
Nov. 15-Dec. 15, 1944, pp. 2-6. Div. 2-130-MI 

138. Underwater Explosives and Explosions, OSRD 5160, 

Interim Report UE-33, NDRC Division 2, UERL, 
Apr. 15-May 15, 1945, pp. 25-30. Div. 2-130-MI 

139. Depth of Detonation of Mark f7 Depth Bombs with 
Mark 23 f Fuzes When Dropped from About 135 Feet 
at Air Speeds of About 150 Knots; Summary of Results 
by Sound Ranging, W. G. Schneider, Report TM-4, 
NDRC Division 2 , UERL, August 1944. 

140. Bombing Accuracy as Determined by Overhead Photographs 
for Mark f7 Depth Bomb When Dropped from About 
135 Feet at Air Speeds of About 150 Knots, Paul M. Fye, 
Report TM-7, NDRC Division 2, UERL, October 1944. 

141. Underwater Travel-Time of Mark f7 Depth Bombs with 
Mark 23 f Fuzes When Dropped from About 135 Feet 
at Air Speeds of About 150 Knots, R. R. Halverson, 
Report TM-3, NDRC Division 2, UERL, July 1944. 

142. Analysis of the Spray Dome, W. G. Walker, SS Informal 
Report 1291, Lrndex 102, December 1919. 

143. A Method of Determining Depth of Underwater Explosions, 
R. A. Shaw, Report H/ARM/Res 1. B3884, Marine 
Aircraft Experimental Establishment, Helensburgh, 
Great Britain, 1941. 

144. A Further Investigation into Dome Analysis Method of 
Determining the Depth of Underwater Explosions, R. A. 
Shaw, Report S. W. 23, H/ARM/Res 3., B3885, 
April 1942. 

145. Underwater Explosives and Explosions, OSRD 5433, 

Interim Report UE-36, NDRC Division 2, UERL, 
July 15-Aug. 15, 1945, pp. 24-28. Div. 2-130-MI 

146. Underwater Trajectory of the Squid Projectile: Part I, 
the Depth Sinking Time Curve, W. G. Schneider and 
R. H. Cole, OSRD 6257, NDRC A-379. 

147. Preparation of Charges for the Study of Explosion 

Phenomena at the Underwater Explosives Research Lab¬ 
oratory, Philip Newmark and Ernest L. Patterson, 
OSRD 6259, NDRC A-381, OEMsr-569 and NOrd- 
9500, WHOI, March 1946. Div. 2-133-M3 


Chapter 2 

1 . Air Burst for Blast Bombs, OSRD 4943, NDRC A-322, 

OEMsr-260, OEMsr-569, and others, Service Projects 
OD-03, NO-224, and others PITS, WHOI, and others, 
April 1945. (A compilation of papers presented at the 
NDRC Division 2 symposium on air burst for blast 
bombs.) Div. 2-110-M5 

2. The Hydrodynamic Theory of Detonation and Shock 

Waves, George B. Kistiakowsky and E. Bright Wilson, 
Jr., OSRD 114, Final Report 52, NDCrc-30, Service 
Projects OD-02 and OD-03, NDRC Division 8 , HU, 
Aug. 15, 1941. Div. 2-131-MI 

3. Calculation of the Detonation Properties of Some Service 

Explosives, Stuart R. Brinkley, Jr., and E. Bright W ilson, 
Jr., OSRD 1510, NDCrc-168, Service Projects OD-02 
and NO-144, HU, June 14, 1943. Div. 8-502-M2 



BIBLIOGRAPHY 


483 


4. The Use of the Rotating Drum Camera for the Measurement 
of the Velocities of Shell or Bomb Fragments, G. H. 
Messerly, OSRD 3900, OEMsr- 20 ‘ 2 , Service Projects 
NO-110, NO-167, and OD-152, ERL, April 1944. 

Div. S-401-M3 

5. Fragment Velocity and Panel Penetration: A Comparison 
of Haleite and Ednatol with Service Filling, Part I, 
R. W. Drake, OSRD 1964, OEMsr-202, Service Projects 
OD-152 and NO-110, ERL, Oct, 30, 1943. Div. 8-105-M2 

6 . Fragment Velocity and Panel Penetration: A Comparison 
of Haleite and Ednatol with Service Filling, Part II, 
R. W. Drake, OSRD 1965, OEMsr-202, Service Projects 
OD-152 and NO-110, ERL, Oct. 30, 1943. 

Div. 8-405-M3 

7. Fragment Velocity and Panel Penetration: A Comparison 
of Haleite and Ednatol with Service Filling, Part III, 
R. W. Drake, OSRD-2071, OEMsr-202, Service Projects 
OD-152 and NO-110, ERL, Nov. 29, 1943. 

Div. S-405-M4 

S. Fragment Velocity arid Panel Penetration: A Comparison 
of Haleite and Ednatol with Service Filling, Part IV, 
R. W. Drake, OSRD 3022, OEMsr-202, Service Projects 
OD-152 and NO-110, ERL, Dec. 18, 1943. Div. 8-405-M5 

9. Fragment Velocity and Panel Penetration: A Comparison 
of Haleite and Ednatol with Service Filling, Part V and 
Part VI, R. W. Drake, OSRD 3079, OEMsr-202, 
Service Projects OD-152 and NO-110, ERL, Jan. 3, 
1944. Div. 8-405-M6 

10. Detonation, Fragmentation , and Air Blast, Interim Re¬ 

ports DFA-1 to 11, DF -12 to 20, Service Projects OD-02, 
OD-03, and others, NDRC Division 8 , August 1943- 
August 1945. Div. 8-500-M2 

11. Theory of Shock Waves, John von Neumann, OSRD 1140, 

OEMsr-218, Service Projects OD -02 and OD-03, NDRC 
Division 8 , Institution for Advanced Study, Jan. 29, 

1943. Div. 2-120-M2 

12. A Modification of the Impulse Criterion for Blast Damage, 
D. C. Christopherson, R. C. 349, A. C. 2790, S. D. 139, 
December 1942. 

13. The Design and Use of Tourmaline Gauges for Piezoelectric 
Measurement of Air Blast, A. B. Arons and C. W. Tait, 
OSRD 6250, NDRC A-372. 

14. Development of Explosion.Pressure Gauges and Recording 

Equipment, OSRD 1739, OEMsr-596, Service Projects 
OD-03 and NO-144, NDRC Division 8 , SOG, Aug. 24, 
1943. Div. 2-111.11-M3 

15. Development of Blast Pressure Gauges and Recording 

Equipment, Daniel Silverman and H. M. Lang, OSRD 
4619, NDRC A-313, OEMsr-596, Service Project OD-03, 
SOG, January 1945. Div. 2-111.11-M6 

16. Development of Blast Pressure Gauges and Recording 
Equipment, Part II, H. M. Lang and Daniel Silverman, 
OSRD 6317, NDRC A-352, OEMsr-596, Service Projects 
OD-03, NO-283, and others, SOG, November 1945. 

Div. 2-111.11-M7 

17. Construction of Tourmaline Gauges for Piezoelectric 
Measurement of Explosion Pressures, Clifford Frondel, 
OSRD 6256, NDRC A-378, OEMsr-569, Service Projects 
OD-03 and NO-223, WHOI, January 1946. 

Div. 2-111.11-M8 

18. Characteristics of Air-Blast Gauges: Response as a Func¬ 

tion of Pressure Level, A. B. Arons, C. W. Tait, G. K. 
Fraenkel, and Iv. M. Doane, OSRD 4875a, AES- 8 a, 
March 1945. Div. 2-100-MI 

19. Characteristics of Air-Blast Gauges, II: Response as a 
Function of Pressure Level, C. W. Tait and W. D. 
Kennedy, OSRD 5271c, AES-1 lc, June 1945. 

Div. 2-100-MI 


20. Shock Tube, Piezoelectric Gauges and Recording Apparatus, 
J. C. Fletcher, W. T. Read, R. G. Stoner, and D. K. Weiner, 
OSRD 6321, NDRC A-356, OEMsr-260, Service Projects 
OD-03 and NO-283, PUS, February 1946. 

Div. 2-111.11-M10 

21 . The Measurement of Transient Stress, Displacement and 

Pressure, Curtis W. Lampson, OSRD 756, NDRC A-73, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
PUS, August 1942. Div. 2-111.12-MI 

22. Blast Performances of H. E. Bombs and Charges. Methods 
Used in the ARD for Recording Blast Characteristics in 
Air Using Quartz Piezoelectric Gauges, Explosives Report 
48/44, ARD, April 1944. 

23. The Measurement of Blast Pressures in Aberdeen Tests, 

Curtis W. Lampson, OSRD 1465, NDRC A-186, 
OEMsr-260, Service Projects OD-79, NO-11, and others, 
PUS, June 1943. Div. 2-111-M2 

24. Cable Compensation for Piezoelectric Gages, Curtis W. 

Lampson, OSRD 1179, NDRC A-63M, OEMsr-260, 
Service Projects CE- 2 , NO-11, and others, PUS, 
January 1943. Div. 2-111.11-M2 

25. The Use of Electrical Cables with Piezoelectric Gauges, 
R. H. Cole, OSRD 4561, NDRC A-306, OEMsr-569, 
Service Project NO-223, WHOI, January 1944. 

Div. 2-111.11-M4 

26. Apparatus for the Measurement of Air-Blast Pressures by 
Means of Piezoelectric Gauges, G. K. Fraenkel, OSRD 
6251, NDRC A-373. 

27. Mobile Oscillograph Laboratory, Curtis W. Lampson and 
Walker Bleakney, OSRD 4570, NDRC A-307, OEMsr- 
675, Service Project OD-79, PUS, January 1945. 

Div. 2-111.12-M3 

28. A Method of Low-Frequency Compensation of Amplifiers 

to Reproduce Transients of Long Duration, Curtis W. 
Lampson, OSRD 3293, NDRC A-255, OEMsr-260, 
Service Projects CE-5, NO- 12 , and others, PUS, 
March 1944. Div. 2-111.12-M2 

29. Portable Oscillographic Equipment for the Measurement 

of Blast Pressures, Curtis W. Lampson, OSRD 5144, 
AES-lOa, May 1945. Div. 2-100-MI 

30. Small Charge Air Blast Experiments, George T. Reynolds, 
OSRD 1518, NDRC A-191, OEMsr-260, Service 
Projects OD-79, NO-11, and others, PUS, June 1943. 

Div. 2-110-MI 

31. FM System of Blast Measurement, Phil Weiss, Report 
492, BRL, October 1944. 

32. An Improved Indicator for Measuring Static and Dynamic 
Pressure, C. E. Grinstead, R. N. Frawley, F. W. Chap¬ 
man, and H. F. Shultz, (presented at the National 
Material Meeting of the Society of Automotive Engi¬ 
neers at Detroit,) June 1944. 

33. Report on the Use of Condenser Gauges as Pressure- 
Sensitive Indicators in Pressure Barrels and Automatic 
Weapons, RD Explosives Report 255/42, Research 
Department, Woolwich, September 1942. 

34. A Condenser-Type FM Ga uge for Blast Pressure Measure¬ 

ments, Lincoln G. Smith, OSRD 6320, NDRC A-355, 
OEMsr-260, Service Projects OD-03 and NO-283, PUS, 
January 1946. Div. 2-111.11-M9 

35. The Use of General Motors Capacitance Pressure Gauges 
for Internal Ballistics Measurements on Rocket Propellants, 
Charles G. Sage, OSRD 5750, OEMsr-202, Service 
Project OD-14, ERL, Nov. 1, 1945. Div. 8-607.5-M5 

36. The Taylor Model Basin Diaphragm Blast Gauge, B. Suss- 
holz, Report 508, DTMB, December 1943. 

37. Comparison Tests of the Stanolind Oil and Gas Company 
Piezoelectric Blast-Pressure Recording Instruments and 
the David Taylor Model Basin Diaphragm-Type Blast- 




484 


BIBLIOGRAPHY 


Pressure Recording Equipment, Daniel Silverman and 
H. M. Lang, OSRD 4257b, AES-3b, October 1944. 

Div. 2 - 100 -MI 

38. Construction arid Performance of the NOL Crusher Gauge, 
Report 751, NOL, 1943. 

39. Consistency of the NOL Ball-Crusher Gauge, R. H. Brown, 
Explosives Report 1, NAVORD, February 1944. 

40. Theory of the Ball-Crusher Gauge, G. K. Hartman, 
Memorandum for File, NAVORD, September 1942. 

41. Mechanical Air-Blast Gauges, W. E. Gordon, and P. E. 
Shafer, OSRD 6249, NDRC A-371. 

42. Measurement and Analysis of the Gun-Blast Pressure, 
DTMB, Bureau of Ships, Navy Department , August 1942. 

43. A Mechanical Instrument for Recording the Positive 
Impulse in a Blast Wave, AC-6655, RRL, July 1944. 

44. The Calibration of Paper Blast Meters, R. G. Sachs, 
Report 472, BRL, June 1944. 

45. Theory, Calibration and Use of Diaphragm Blast Meters, 
W. T. Read, OSRD 6463, NDRC A-392, OEMsr-260, 
Service Project OD-03, PUS, April 1946. 

Div. 2-111.12-M5 

46. An Improved Method jor the Measurement of Blast from 
Bombs, T. D. Carr, M. Schwarzschild, and Phil Weiss, 
Report 336. BRL, April 1943. 

47. Review of Flame Velocity Measurements from Bombs and 
Bare Charges up to January 31, 1043, AC-3894, RRL, 
April 1943. 

4S. The Formation of Mach or Bridge Waves. I Single Plane- 
Ended Cylinders, D. W. Woodhead and R. Wilson, 
AC-7647, January 1945. 

49. Photographic Investigation of the Reflection of Plane Shocks 

in Air, Lincoln G. Smith, OSRD 6271, NDRC A-350, 
OEMsr-260, Service Projects NO-144 and OD-G3, PUS, 
November 1945. Div. 2-120-M8 

50. Shadowgraphic Determination of Shock Wave-Strength, 
Explosives Research Report 11, NAVORD. 

51. Spark Photographs of the Mach Effect, Paul Libessart, 
Report RC-417, May 1944. 

52. Photographic Observation of a Shock Crossing a Gas 

Boundary, D. K. Weimer, Lincoln G. Smith, OSRD 
6007b, AES-14b, September 1945. Div. 2-100-MI 

53. High-Speed Cameras for Measuring the Rate of Detonation 
in Solid Explosives, W. Payman, V . C. F. Shepherd, and 
D. W. Woodhead, Paper 99, Safety in Mines Research 
Board, 1937. 

54. Construction arid Operation of the Rotating Mirror Camera, 

S. J. Jacobs, OSRD 5614, OEMsr-202, Service Projects 
NO-291 and OD-04, Carnegie Institute of Technology, 

Jan. 2, 1946. Div. 8-401-M4 

55. Shock Wave Studies with the Rotating Drum Camera,, 

Duncan P. MacDougall, Elizabeth M. Boggs, and G. H. 
Messerly, Interim Report DF-12, NDRC Division 8 , 
August 1944. Div. 8-500-M2 

56. High-Speed Photographic Techniques, G. M. Cooke, 
Report 20, Valcartier (Que) Ballistic Laboratory, 
December 1944. 

57. The Flash Photography of Detonating Explosives, G. H. 

Messerly, OSRD 1488, OEMsr-202, Service Project 
OD-02, ERL, June 1943. Div. 8-401-M2 

5S. Physical Optics, R. W. Wood, The MacMillan Company, 
1934, p. 93. 

59. Study of Shock Waves by Interferometry, J. R. Winckler, 

C. C. Van Voorhis, H. Panofsky, and R. Ladenburg, 
OSRD 5204, NDRC A-332, OEMsr-260, Service Projects 
NO-208 and OD-03, PUS, June 1945. Div. 2-120-M7 

60. Study of Shock Waves by Interferometry, R. Ladenburg, 

C. C. Van Voorhis, and J. R. Winkler, OSRD 4514a, 
AES-5a, December 1944. Div. 2 - 100 -MI 


61. Construction of Resistance Strain Gauges, Robert J. 

Hansen, OSRD 1003, NDRC A-59M, OEMsr-260. 
Service Projects CE-5, NO- 11 , and others, PUS, 
November 1942. Div. 2 - 11 1.1 1 -Ml 

62. A Preliminary Study of Plane Shock Waves Formed by 
Bursting Diaphragms in a Tube, George T. Reynolds, 
OSRD 1519, NDRC A-192, OEMsr-260, Projects NO- 
144 and P2-207, PUS, June 1943. Div. 2-120-M3 

63. Shock Waves in Air: A Method of Gauge Calibration Based 

on Velocity Measurements, W. T. Read, Jr., OSRD 
4076b, AES-16, August 1944. Div. 2-100-MI 

64. Pressures Behind a Shock Wave Computed for Velocity 

Measurements in the Blast Tube and the Correction for 
Humidity , W. T. Read, Jr., OSRD 4257c, AES-3c, 
October 1944. Div. 2-100-MI 

65. Determination of Shock Wave Pressure in the Blast Tube 
as a Function of Compression-Chamber Pressure, W. T. 
Read, Jr., OSRD 4514b, AES-5b, December 1944.* 

Div. 2-100-Ml 

66 . Pressure-Velocity Relation for Shock Waves in a “van 

der Wauls” Gas, W. T. Read, Jr., OSRD 5011a, AES-9a, 
April 1945. Div. 2-100-MI 

67. Effect of Temperature on Gauge Calibration, W. T. Read, 
Jr., OSRD 5144b, AES-lOb, May 1945. 

Div. 2-100-MI 

68 . An Experimental Determination of the Point of Catchup 

of the Rarefaction Wave and the Impulse of the Shock Wave 
in a Tube, Curtis W. Lampson, OSRD 4754a, AES-7a, 
February 1945. Div. 2-100-MI 

69. On the Estimation of Perturbations Due to Flow Around 

Blast Gauges, J. K. Lome MacDonald and Samuel A. 
Schaaf, OSRD-5639, OEMsr-945, Note 22 , AMP, 
September 1945. AM P- 101 . 1 -Ml 8 

70. Prediction of Blast Damage for Experimental Results, 
REN 367, Ministry of Home Security, April 1944. 

71. Observations of Blast Damage in Great Britain from 
German Weapons with Aluminized and Non-aluminized 
Loadings, REN 368, Ministry of Home Security, 
April 1944. 

72. Damaging Effect of Known 8,000-Lb HC Bombs, AC-4572 
(R. E./H. 33), Ministry of Home Security, August 1943. 

73. Effectiveness of 12,000-Lb HC Bombs Filled Torpex 2/ 
Amatex 9 Against Single Story Reinforced Concrete Build¬ 
ings, REN 345, Ministry of Home Security, March 1944. 

74. Radius of Damage from 12,000-Lb HC Bombs Filled 
Amatex 9. Operational Results, REN 316, Ministry of 
Home Security, January 1944. 

75. Study of the Physical Vulnerability of Military Targets 

to Various Types of Aerial Bombardment, Walker 
Bleakney, OSRD 6444, NDRC A-385, OEMsr-260. 
Service Project AN-29, Weapons Effect Group, PUS, 
January 1946. Div. 2-530-M3 

76. Reactions of Simple Systems under Blast Loading, 

D. Montgomery and A. H. Taub, OSRD 5393a, AES-12a. 

July 1945. Div. 2-100-MI 

77. Remarks on Reactions under Blast Loading, D. Mont¬ 

gomery and A. H. Taub, OSRD 6007a, AES-14a, 
September 1945. Div. 2-100-MI 

78. The Order of Effectiveness of Explosives in Air-Blast, 
W. D. Kennedy, OSRD 6252, NDRC A-374. 

79. Measurement of Blast Pressures from 4,000-Lb Bombs , 

E. Bright Wilson, Jr., OSRD 1153, OEMsr-334, Service 

Projects OD-02 and OD-03, NDRC Division 8 , HU, 
Jan. 23, 1943. Div. 2-111-MI 

80. Blast Pressures and Momenta from Some Large Bombs . 

E. Bright Wilson, Jr., and W. D. Kennedy, OSRD 3046, 
OEMsr-334, Service Projects OD-02 and OD-03, NDRC 

Division 8 , HU, Nov. 17, 1943. Div. 2-111-M4 



BIBLIOGRAPHY 


485 


81. Small Charge Air Blast Measurements: Order of Effective¬ 
ness of Explosives, W. D. Kennedy, R. F. Arentzen, 
G. K. Fraenkel, and Paul C. Cross, OSRD 4076d, 
AES-ld, August 1944. Div. 2-100-MI 

52. Order of Effectiveness of Explosives, 77, W. D. Kennedy, 
R. F. Arentzen, G. K. Fraenkel, and Paul C. Cross, 
OSRD 4147a, AES-2a, September 1945. Div. 2-100-MI 

53. Order of Effectiveness of Explosives, IV. Peak Pressures 

and Positive Impulses in the Blast from 500-Lb Bombs 
Filled with HBX, Torpex 2, Composition B, and Tritonal, 
W. D. Kennedy, R. F. Arentzen, and C. W. Tait, OSRD 
4649a, AES- 6 a, January 1945. Div. 2-100-MI 

54. Survey of the Performance of TNT/Al on the Basis of 

Air Blast Pressure and Impulse, W. D. Kennedy, OSRD 
4649b, AES- 6 b, January 1945. Div. 2-100-MI 

85. The Air-Blast Performance of Some High Explosives, 
W. D. Kennedy, OSRD 4754b, AES-7b, February 1945. 

Div. 2-i00-Ml 

86 . Order of Effectiveness of Explosives, V. Comparison of 

Blast Pressures and Impulses of PTX-l and PTX-2 with 
Those of HBX, Composition B and TNT, C. W. Tait, 
W. E. Curtis, and W. D. Kennedy, OSRD 4875b, AES- 
8 b, March 1945. ‘ Div. 2-100-MI 

87. Order of Effectiveness of Explosives, III, W. D. Kennedy, 

OSRD 4356, AES-4. Div. 2-100-MI 

S 8 . The Effect of Air Burst on the Blast from Bombs and Small 
Charges, OSRD 4246, OEMsr-569 and OEMsr-596, 
Service Project OD-03, NDRC Division 8 , UERL, 
WHOI, and SOG, Oct. 16, 1944. Div. 2-110-M3 

89. Air-Blast Measurements with Tritonal Containing Flake 
Aluminum and with TNT/Al 60 / Iff) and TNT/Al 40/60, 

C. W. Tait and W. D. Kennedy, OSRD 5271d, AES-1 Id, 

June 1945. Div. 2-100-MI 

90. Air Blast Measurements of f-Lb Spherical Pentolite 
Charges and Cylindrical Charges of Pentolite, Composition 
B and TNT, R. F. Arentzen and W. D. Kennedy, 
OSRD 5271e, AES-lle, June 1945. Div. 2-100-MI 

91. Air Blast Measurements of Various Explosives as a 
Function of Atmospheric Pressure, H. M. Long and 
I. Silverman, OSRD 6007c, AES-14c, September 1945. 

Div. 2-100-Ml 

92. Small Charge Air Blast Measurements: Order of Effective¬ 
ness of Explosives, Paul C. Cross, W. D. Kennedy, and 

D. F. Hornig, OSRD 3479, OEMsr-569, Service Projects 

OD-03 and NO-144, NDRC Division 8 , WHOI, Apr. 1 , 
1944. Div. 2-110-M2 

93. Calculation of the Detonation Velocities of Some Pure 

Explosives, Stuart R. Brinkley, Jr., and E. Bright Wilson, 
Jr., OSRD 1707, NDCrc-168, Service Projects OD-02 
and NO-144, HU, Aug. 12, 1943. Div. 8-501-M4 

94. Bombs, 500-Lb M. C. Mk III, Blast Performance of 
Torpex Mixtures Containing 0-42% of Aluminum, AC- 
8131, SD-543, March 1945. 

95. Bombs, H. C. 4,000-Lb Mark IV Static Detonation Trials 
of Minol with Aluminum Content Varying from 0-28%, 
Explosives Report 68/44, ARD, July 1944. 

96. Bombs, 500-Lb M. C. Mark III, Filled Minol Mixtures 
Containing 0-28% Aluminum Powder, AC-5861, Explo¬ 
sives Report 23/44, ARD, February 1944. 

97. Bombs, HC4,000-Lb Mark IV, TNT/Al 70/30, TNT/Al 
75/25, TNT/Al 80/20, Static Detonation Trials, AC- 
7944, SD-533, March 1945. 

98. Bombs, 500-Lb M. C. Mark III Blast Performance of 
TNT/Al Mixtures Containing 0-40% of Aluminum, 
AC-7073, Explosives Report 112/44, ARD, September 
1944. 

99. Blast and Fragment Velocity Measurements on 500-Lb 
GP Bombs of Various Loadings, R. G. Sachs and W. P. 


Bidelman, Report 500, BRL, November 1944. 

100. The Effect of Addition of Various Amounts of Aluminum 

to TNT, Interim Report DFA-10, NDRC Division 8 , 
UERL. Div. 8-500-M2 

101. Explosive Compositions, Interim Report PT-25, NDRC 

Division 8 , ERL. Div. 8-109-M3 

102 . Measurements of Blast from 4,000-Lb HC Bombs with 
Minol-2 ( 36-Dust Al) and 60/40 RDX/TNT Fillings, 
AC-5963, March 1944. 

103. Velocities of Shocks Produced in Air from Plane-Ended 

Charges, Elizabeth M. Boggs, M. D. Hurwitz, and H. A. 
Strecker, Interim Report DF-19, NDRC Division 8 , 
July 1945. Div. 8-500-M2 

104. Application of the Law of Dynamical Similarity to the 
Blast Characteristics from Cylindrical Bare Charges of 
RDX/TNT, 60/40 Weighing between 8 and 550 Lbs and 
Fired Resting on the Ground, Explosives Report 147/44, 
AC-7673, ARD. 

105. Methods for Computing Data on the Terminal Ballistics 
of Bombs. II. Estimation of the Air Blast, U. Fano, 
Report 524, BRL, February 1945. 

106. Measurement of Blast Pressure f rom 66-Lb Bare Charges 
of 60/40 RDX/TNT, AC-4657, RRL, July 1943. 

107. Contribution of Afterburning to Blast Pressure and Impulse, 
W. E. Gordon, OSRD 4147b, AES-2b, NDRC Division 2 . 

Div. 2-100-MI 

108. Note on the Contribution of the Afterburning of Explosive 
Products to the Positive Impulses in the Blast, AC-3812, 
RRL, March 1943. 

109. Measurements of Blast Pressures from Standard Cased 
Charges of Various Charge-Weight Ratios, AC-3435, 
MOS/193/145, RRL, January 1943. 

110. The Effect of Charge Weight Ratio on Equivalent Charge 
Weight, REN 460, Ministry of Home Security, April 1944. 

111. Dependence of Positive Impulse of Blast on Charge Weight 

Ratio, Henry Scheffe, OSRD 4356d, AES-4d, November 
1944. ‘ Div. 2-100-MI 

112. Relation Between Positive Blast Impulse and Charge Weight 

Ratio for Bombs, E. J. Tan, OSRD 4356e, AES-4e, 
November 1944. Div. 2-100-MI 

113. Bombs, HC, 4000 -Lb of Increased Charge-Weight Ratio. 
Static Detonation Trials of Bombs with ]/%-In. Mild Steel 
and 5/16-In. Aluminum Alloy Cases, AC-7284, ARD, 
October 1944. 

114. Bombs, 500-Lb MC Filled Minol-2 and Amatol 60/40. 
Effect of Cast Aluminum Alloy Case on Positive Blast 
Intensity, AC-6949, ARD, August 1944. 

115. Measurements of the Air Blast from Mark 6 and Mark 8 
Depth Charges, Filled with TNT and RDX-Composition B 
with Steel, Aluminum and Plastic Cases, W. P. Bidelman, 
Report 502, BRL, November 1944. 

116. Blast Measurements of J. B. 2 War Heads with Steel and 
Aluminum Casings, W. P. Bidelman, Report 540, BRL, 
April 1945. 

117. Tables of the Properties of Air Along the Hugoniot Curve 
and the Adiabatics Terminating in the Hugoniot Curve, 
Stuart R. Brinkley, Jr., John G. Kirkwood, and John M. 
Richardson, OSRD 3550, OEMsr-121 Service Projects 
OD-03, NO-144, and NO-224, NDRC Division 8 , 
Cornell University, Apr. 27, 1944. Div. 2-120-M5 

118. Oblique Reflection of Shocks, John von Neumann, 
Explosives Report BO-12, NAVORD. 

119. Regular Reflection of Shocks in Ideal Gases, H. Polachek, 
R. J. Seeger, Explosives Research Report 13, NAVORD, 
February 1944. 

120. “Uber dasGleitendesElektrischen Funkens,” K. Antolik, 
Poggendorff’s Analen der Physik, Vol. 154, 1875. 

121. “Uber Einige Mechanische Wirkungen des Elektrischen 




486 


BIBLIOGRAPHY 


Funkens,” E. Mach and J. Wosyka, Akademie der 
Wissenschaften, Sitzungsberichte der Wiener, Vol. 72, 
Part 2, 1875. 

122. “Uber die FortpflanzungsgeschwindigkeitvonExplosions- 
schallwellen.” E. Mach and J. Sommer, Akademie der 
Wissenschaften, Sitzungsberichte der Wiener, Vol. 75, 1877. 

123. “Uber die Fortpflanzungsgeschwindigkeit der Funken- 
wellen,” E. Mach, D. Tumlirz, and C. Kogler, Akademie 
der Wissenschaften, Sitzungsberichte der Wiener, Vol. 77, 
1878. 

124. “Uber denVerlauf der Funkenwellen in der Ebene und im 
Raume,” Akademie der Wissenschaften, Sitzungsberichte 
der Wiener, Vol. 77, 1878. 

125. Interference of Shock Waves in Air, E. Bright Wilson, Jr., 
Interim Reports FS-2 and FS-3, NDRC Division 8, 
October 1942 and November 1942. Div. 8-400-Ml 

126. The Interaction of Shock Waves, R. W. Wood, OSRD 
1996, OEMsr-773, Service Projects AN-1 and OD-03, 
NDRC Division 8, Johns Hopkins University, Nov. 4, 

1943. Div. 2-120-M4 

127. On the Conditions for the Existence of Three Shock Waves, 
S. Chandrasekhar, Report 367, BRL, 1943. 

128. Remarks on the Mach Effect, Kurt O. Friedrichs, Report 
M5, AMP, July 1943; Appendix, Report M6, AMP, 
July 1943. 

129. On Nearly Glancing Reflection of Shocks, Valentine Barg- 
mann, OEMsr-1111, Report 108.2R, AMG-Institute for 
Advanced Study, AMP, March 1945. AMP-101.1-M13 

130. Prandtl-Meyer Zones in Mach Reflection, Valentine Barg- 

mann, and D. Montgomery, OSRD 5011b, AES-9b. 
April 1945. Div. 2-100-MI 

131. The Effect of the Height at Which a Bomb Explodes on the 
Blast Pressures, Note ARP/255/RJ, August 1941. 

132. General Estimate of the Results of Experiments with the 
Model Town, REN 110, August 1941. 

133. Ordnance Board (British), Proceeding Q1150, April 1943. 

134. Small Charge Air Blast Experiments: Pea\Pressure as a 

Function of Charge-to-Grownd Distance, DFA-5, UER L, 
January 1944. Div. 8-500-M2 

135. Small Charge Air Blast Measurements: Peak Pressure and 
Positive Impulse as a Function of Charge-to-Ground 
Distance, II, DFA-6, UERL, February 1944. 

Div. 8-500-IM2 

136. Small Charge Air Blast Measurements: Peak Pressure 
and Positive Dnpulse as a Function of Charge-to-Ground 
Distance, III, DFA-7, UERL, March 1944. 

Div. 8-500-M2 

137. Small Charge Air Blast Measurements: Peak Pressure 
and Positive Impulse as a Function of Charge-to-Ground 
Distance, IV, DFA-8, UER L, April 1944. Div. 8-500-M2 

138. The Effect of Height of Detonation on Peak Pressure and 

Positive Dnpulse Measured Close to the Ground, W. D. 
Kennedy and R. F. Arentzen, OSRD 4514d, AES-5d, 
December 1945. Div. 2-100-MI 

139. Peak Pressure Dependence on Height of Detonation, 
A. H. Taub, OSRD 4076a, AES-la, August 1944. 

Div. 2-100-Ml 

140. The Reflection of Shock Waves in Air, Lincoln G. Smith, 

OSRD 4076c, AES-lc, August 1944. Div. 2-100-MI 

141. Impulse Dependence on Height of Detonation, R. G. Stoner 
and A. H. Taub, OSRD 4147c, AES-2c, September 1944. 

Div. 2-100-MI 

142. Mach Reflection of Shock Waves from Charges Detonated 
in Air, R. G. Stoner, OSRD 4257d, AES-3d, October 

1944. Div. 2-100-MI 

143. The Shape of the Shock-Wave Fronts from Charges 

Detonated in Air, R. G. Stoner, OSRD 4514e, AES-5e, 
December 1944. Div. 2-100-MI 


144. Dependence of Optimum Dnpulse on Height of Gauge in 

Air-Burst, R. G. Stoner and A. H. Taub, OSRD 5011c, 
AES-9c, April 1945. Div. 2-100-MI 

145. Effect of Height of Burst in the Positive Dnpulse from 
Bombs, Special Preliminary Report, UERL. 

146. Effects of the Height of Burst on the Positive Impulse from 
Bombs, II, UERL, June 1944. 

147. Effect of Case Weight on the Positive Dnpulse from Bombs 
Filled TNT and Torpex-2, W. D. Kennedy, Technical 
Memorandum 2, UERL, July 1944. 

148. The Effect of Air Burst on the Blast from Bombs arid 
Small Charges. Part II, Analysis of Experimental Results, 
R, R. Halverson, OSRD 4899, NDRC A-320, OEMsr- 
569, Service Project OD-03, WHOI, April 1945. 

Div. 2-110-M6 

149. The Observed Effects of Proximity Fuzing in the 4000-Lb 
HC Bomb, D. G. Christopherson, AC-6442, May 1944. 

150. 26th Report of the Static Detonation Committee Meeting 
Held May 17, 1944, AC-6343, May 1944. 

151. The Blast Effect of Air-Burst Bombs. I History of 
British Experience. II Commentary on American In¬ 
vestigations, D. G. Christopherson, AC-6526, June 1944. 

152. Air Burst Bombs. Statement of the Position on October 20, 

1944, D. G. Christopherson, REN 461. 

153. The Effect of Height of Burst on the Blast Characteristics 
from 67-Lb Bare Charges of RDX/TNT 60/40, Interim 
Report, ARD, December 1944. 

154. Effect of Height of Detonation of Bombs on the Blast 
Pressures and Impulses on Surrounding Buildings — 
Richmond Park l/7th Scale Model Town Tests, AC-8097, 
RRL, March 1945. 

155. Weapon Data — Fire, Impact Explosion, OSRD 6053, 
NDRC Division 2, PL T S, September 1945. 

156. The Effectiveness of Explosives in Enclosed Spaces, W. E. 
Gordon, OSRD 6255, NDRC A-377. 

157. Studies on SBX, Part II. Comparison of Results Obtained 
in Part I with Jones 1 Simplified Theoretical Calculations 
of SBX Pressure-Time Characteristics, C. S. Lu, Report 
167, MRL, January 1945. 

158. Relative Effectiveness of Explosives Fired in Nearly En¬ 

closed Rooms, W. E. Gordon and H. M. Lang, OSRD 
501 Id, AES-9d, April 1945. Div. 2-100-MI 

159. Effect of Confined Blast on Brick Curtain Walls, A. H. 
Taub and J. A. Wise, OSRD 6007d, AES-14d, September 

1945. Div. 2-100-Ml 

160. Development of SBX Fillings, AC-6644, Incendiary 
Projectiles Committee of the Static Detonation Com¬ 
mittee, July 1944. 

161. Dispersion and Combustion of Metallic Powders in Air, 
G. J. Finch, AC-4273, Research and Experiments De¬ 
partment, Ministry of Home Security, June 1943. 

162. Report on Static Trials of SBX-Filled Bombs at the 
Mansion House, Muirburn, REN 353, AC-6147, Research 
and Experiments Department, Ministry of Home 
Security, April 1944. 

163. Static Trials of a Minol-Filled Bomb at the Mansion 
House, Muirburn, REN 356, AC-6148, Research and 
Experiments Department, Ministry of Home Security, 
March 1944. 

164. Note On SBX (with Particular Reference to a Suggested 
Incorporation of Cerium), G. J. Finch, AC-6747, July 1944. 

165. On the Possibility of the Use of Combustibles to Amplify 
the Blast Effect of Bombs, J. E. Mayer, Report 411, 
BRL, October 1943. 

166. Use of Flour and Other Dust Explosives in Attacks on 
Confined Wooden Structures, C. S. Lu, Report 92, MRL, 
June 1944. 

167. Dust Explosion Tests in Wooden Houses Located at TV A 



BIBLIOGRAPHY 


487 


Reservoir Area Near Bryson City, A r . C., C. S. Lu, 
Report 152, MRL, September 1944. 

168. Memorandum on the Latest Dust and Liquid Explosion 
Tests at Factory Mutual Test Station, Norwood, Mass., 
C. S. Lu, MRL, October 1944. 

169. Use of Dust and Liquid Slow Burning Explosives in 
Attacks on Confined Structures, C. S. Lu, Report 183, 
MRL, February 1945. 

170. Development of Salex, Norman J. Thompson, Report to 
W. C. Lathrop, NDRC Division 19, November 1944. 

171. Final Report on Teak, H. J. Billings and S. Edward 
Eaton, Jr., OEMsr-1023, Part IX with Arthur Little, 
Inc., May 1945. 

172. Studies on SBX: Comparison of Various Combustibles 
vs. SBX Under Confined Conditions, W. E. Gordon, 
OSRD 4356a, AES-4a, November 1944. Div. 2-100-MI 

173. The Propagation and Decay of Blast Waves, G. I. Taylor, 
RC-39. 

174. The Formation of a Blast Wave by a Very Intense Explo¬ 
sion, G. I. Taylor, RC-210. 

175. The Development of Suction Behind the Blast Wave in Air 
and the Energy Dissipation, W. G. Penney, RC-260, 
October 1941. 

176. The Numerical Integration of the Equation for a Spherical 
Shock Wave in Air, Oscar K. Rice, Interim Report 
DFA-9, NDRC Division 8, May 1944. Div. 8-500-M2 

177. The Numerical Integration of the Equation for a Spherical 
Shock Wave in Air, R. Grinell and Oscar K. Rice, 
OSRD 4257e, AES-3e, October 1944. Div. 2-100-MI 

178. A New Theory of Shock Wave Propagation with an 
Application to the Shock Wave Produced in Air by the 
Explosion of Cast Pentolite, John G. Kirkwood and Stuart 
R. Brinkley, Jr., OSRD 4257f, AES-3f, October 1944. 

Div. 2-100-Ml 

179. The Time Constant and Positive Impulse According to 
the Theory of Shock Wave Propagation of Blast Waves: 
Results for Cast Pentolite, John G. Kirkwood and Stuart 
R. Brinkley, Jr., OSRD 4356f, AES-4f, November 1944. 

Div. 2-100-Ml 

180. The Calculation of the Time Constant and the Positive 

Impulse from the Peak Pressure-Distance Curves of Blast 
Waves in Air with an Application to Cast TNT, John G. 
Kirkwood and Stuart R. Brinkley, Jr., OSRD 4356g, 
AES-4g, November 1944. Div. 2-100-MI 

181. Theory of the Propagation of Shock Waves from Explosive 

Sources in Air and Water, John G. Kirkwood and Stuart 
R. Brinkley, Jr., OSRD 4814, NDRC A-318, OEMsr-121, 
Service Projects OD-03 and NO-224, Cornell University, 
March 1945. Div. 2-120-M6 

182. Tables and Graphs of the Theoretical Peak Pressure, 
Energies and Positive Impulse of Blast Waves in Air, 
Stuart R. Brinkley, Jr., and John G. Kirkwood, OSRD 
5137, NDRC A-327, OEMsr-121, Service Projects OD-03 
and NO-224, Cornell University, May 1945. 

Div. 2-112-MI 

183. Theoretical Blast Wave Curves for Cast TNT, John G. 
Kirkwood and Stuart R. Brinkley, Jr., OSRD 5481, 
NDRC A-341, OEMsr-121, Service Projects OD-03 and 
NO-224, Cornell University, August 1945. Div. 2-112-M2 

184. The Pressure Distance Relation for TNT, Determined by 
Measurements of Shock Velocity, R. G. Stoner, OSRD 
6637, NDRC A-474. 

185. Shock Wave Studies with the Rotating Drum Camera, 

Duncan P. MacDougall, Elizabeth M. Boggs, and G. H. 
Messerly, Interim Report DFA-12, NDRC Division 8, 
August 1944. Div. 8-500-M2 

186. Piezoelectric Measurements of Pressure Impulse and Shock 
Wave Velocity Close to a One-Half Pound Charge, Interim 


Report DFA-7, NDRC Division 8, UERL, March 1944. 

Div. 8-500-M2 

187. Measurements of Blast Pressure from Bore Charges of 
60/4-0 RDX/TNT, Fired at Richmond Park in the Period 
April 19-25,1943, ARP/408/HS. DJL, RRL, August 1943. 

188. 67-Lb Bore Charges of RDX/TNT 60/40 Type D, 100, 
Fired at Millersford Between September 25, 1943 and 
January 31, 1944 > Explosive Report 24/44, AC-5853, 
ARD, February 1944. 

189. Blast Measurements from Card Cased Cylindrical Charges 
of About 60-Lb of Some Service High Explosives, Report 
113/44, AC-7058, ARD, October 1944. 

190. The Air Blast from Line Charges, G. K. Fraenkel and 
W. D. Kennedy, OSRD 6253, NDRC A-375. 

191. The Blast Wave in Air Produced by Line Charges, Stuart 
R. Brinkley, Jr., John G. Kirkwood, OSRD 5659, NDRC 
A-343, OEMsr-121, Service Projects OD-03 and NO-224, 
Cornell University, October 1945. Div. 2-110-M4 

192. Aerial Bombardment of Mine Fields, Report 860, The 
Technical Staff, The Engineer Board, Corps of Engineers, 
U. S. Army, August 1944. 

193. Third I nterim Report. Equipment for the Passage of Enemy 
Minefields, Report 861, The Technical Staff, The 
Engineer Board, Corps of Engineers, U. S. Army, 
September 1944. 

194. Project 112—Aerial Bombing of Mine Fields, Joint Army- 
Navy Experimental and Testing Board, Janet Progress 
Report, Jan-Pro/15, June 1945. 

195. Clearance of Mines by Rocket Barrages from the Woof us, 

NDRC 161.1R, OEMsr-860, SRG-P 150, AMP, August 
1945. AMP-902-M5 

196. Detonating Cord Cable Kit, Report 906, The Technical 
Staff, The Engineer Board, Corps of Engineers, U. S. 
Army, January 1945. 

197. Snake, Mineclearing, Antipersonnel Ml, War Depart¬ 
ment Technical Bulletin, TB Eng 65, February 1945. 

198. First Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 842, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
July 1944. 

199. Second Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 850, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
August 1944. 

200. Fourth Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 875, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
October 1944. 

201. Fifth Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 888, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
November 1944. 

202. Sixth Interim Report; Equipment for the Passage of 
Enemy Mine Fields , Report 894, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
December 1944. 

203. Seventh Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 905, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
January 1945. 

204. Eighth Interim Report; Equipment for the Passage of 
Enemy Mine Fields, Report 928, The Technical Staff, 
The Engineer Board, Corps of Engineers, U. S. Army, 
April 1945. 

205. Snake, Demolition, M2A1, War Department Technical 
Bulletin, TB Eng 47, October 1944. 

206. Snake, Demolition, M3, War Department Technical 
Bulletin, TB Eng 60, March 1945. 


i'ONFIDENT [AM 





488 


BIBLIOGRAPHY 


207. Mine-Clearing Dragon, M-l, Report 929, The Technical 
Staff, The Engineer Board, Corps of Engineers, U. S. 
Army, May 1945. 

208. Piezoelectric Measurements of Blast Pressures in M-4 

Tank from Explosive Charges Detonated Outside of Vehicle, 
Daniel Silverman and H. M. Lang, OSRD 4307, NDRC 
A-297, OEMsr-596, Service Project OD-03, SOG, 
November 1944. Div. 2-111.11-M5 

209. The Effect of Blast on Indicator Mines, E. Bright Wilson, 
Jr., A. H. Taub, Curtis W. Lampson, and Thomas 
Bardeen, OSRD 4276, OEMsr-266, Service Project 
OD-03, NDRC Divisions 2 and 17, PUS, SOG, and 
Gulf Research and Development Company, Sept. 28, 

1944. Div. 2-113-MI 

210. The Effect of Shock Impulse on Anti-Tank Mines, Parts I 
and II, Thomas Bardeen, OSRD 6078, OEMsr-266, 
Gulf Research and Development Company, Oct. 15, 

1945. Div. 17-122.1-M3, M4 

211. Expected Clearance of German and Japanese Anti-Tank 

and Anti-Personnel Mines by Explosive Mine-Clearing 
Devices, Statistical Research Group, AMP 178.1R, PUS, 
June 1945. AMP-902-M3 

212. The Detonation of TMi-43 Indicator by Blast, J. L. 
Brenner, OSRD 5179, NDRC A-331, OEMsr-260, 
Service Project OD-03, PUS, June 1945. 

Div. 2-111.12-M4 

213. The Detonation of Universal Indicator Mine by Blast from 
Point Charges, j. L. Brenner, OSRD 5271b, AES-1 lb. 

Div. 2-100-Ml 

214. The Effect of Line Charges on Universal Indicator Mine, 

J. L. Brenner and A. H. Taub, OSRD 5144c, AES-lOc, 
May 1945. Div. 2-100-MI 

215. Theoretical Aspects of the Blast Detonation of Teller Mines, 
E. B. Philip, PF 3902/89. 

216. On a New Criterion for Measuring the Efficiency of an 
Explosive Hose, F. N. David, REN 486, AC-7843, 
Ministry of Home Security, February 1945. 

217. The Effect of the “Probability Dip ” of Alternating the 
Nature and Weight of Filling of the Conger, J. L. Alexander, 
D. C. Brettell and F. N. David, REN 485, AC-7842, 
Ministry of Home Security, February 1945. 

218. Empirical Laws for Blast Pressures from Line Charges 
of Ammonal 704 B, E. B. Philip, RC-426, September 1944. 

219. Blast Pressures and Positive Impulses from Cordex Line 
Charges Fired in Air, Undex 101, RRL, July 1944. 

220. The Effect of Raising a Line Charge, F. N. David, 
REN 348, Ministry of Home Security, March 1944. 

221. The Dependence of Blast on Ambient Pressure and 
Temperature, R. G. Sachs, Report 466, BRL, May 1944. 

222. The Effect of Altitude on the Peak Pressure and Positive 

Impulse from Blast Waves in Air, John G. Kirkwood, 
and Stuart R. Brinkley, Jr., OSRD 5271a, AES-lla, 
June 1945. Div. 2-100-MI 

223. An Examination of the Symmetry of the Positive Blast 
Impulse Intensity Around Bombs MC 500-Lb, Mark III, 
Amatol 60/40, Explosives Report 381/43, ARD, Novem¬ 
ber 1943. 

224. Charge Orientation Tests, George T. Reynolds, OSRD 
1532, NDRC A-193, OEMsr-260, Service Projects OD- 
76, NO-11, and others, PUS, July 1943. Div. 2-111-M3 

225. Measurements of Blast from Four 1000-Kg German S. B. 
Bombs Fired at Shoeburyness in the Periods 1st to 9th, 
AC-8181, MOS/442/DJL.EK, RRL, April 1945. 

226. Shock Wave Studies with the Rotating Drum Camera, 
Duncan P. MacDougall and G. H. Messerly, Interim 
Report DFA-10, NDRC Division 8, June 1944. 

Div. 8-500-M2 

Blast Pressures Measured Near the Jets from 5-Inch Spin- 


Stabilized Rockets, R. F. Arentzen, OSRD 5144d, AES- 
lOd, May 1945. Div. 2-100-MI 

228. Construction and Characteristics of Model Ammunition 

Storage Magazines, Nathan M. Newmark, C. P. Atkins, 
and E. E. Bauer, OSRD 6318, NDRC A-353, OEMsr- 
1476, Service Project AN-28, University of Illinois, 
November 1945. Div. 2-540-M2 

229. Observations on the First Model Igloo Test at Camp 

Edwards, on October 23, 1945, W. E. Gordon, Technical 

Memorandum 13, UERL, December 1945. 

230. The Probability of Propagation of an Explosion in a Field 

of Storage Magazines, E. Bright Wilson, Jr., OSRD 527 If, 
AES-1 If, June 1945. Div. 2-100-MI 

Chapter 3 

1. Final Report on Effects of Explosives in Earth, Curtis W. 
Lampson, OSRD, NDRC Report. 

2. “A Study of Blasting Recorded in Southern California,” 
Harry O. Wood and Charles F. Richter, Bulletin of 
Seismological Society of America, Vol. 21, No. 1, March 
1931, p. 28. 

3. Vibrations Caused by Blasting and Their Effect on Struc¬ 
tures, Edward H. Rockwell, Hercules Powder Company, 
Wilmington, December 1934. 

4. Earth Vibrations Caused by Quarry Blasting, F. W. Lee, 
J. II. Thoenen, and Stephen L. Windes, Report of 
Investigation 3319, L T . S. Bureau of Mines, November 
1936. 

5. Earth Vibrations Caused by Quarry Blasting, J. R, 
Thoenen and Stephen L. Windes, Report of Investigation 
3353, U. S. Bureau of Mines, November 1937. 

6. Earth Vibrations Caused by Quarry Blasting, J. R. 
Thoenen and Stephen L. Windes, Report of Investigation 
3407, XJ. S. Bureau of Mines, June 1938. 

7. Seismic Effect of Quarry Blasting, J. R. Thoenen and 
S. L. Windes, Bulletin 442, U. S. Bureau of Mines, 1942. 

8. Survey Test on Open Trench after Bombing — Stewartly 
( Clay Soil), R.C. 64, Research and Experiments Branch, 
Ministry of Home Security, November 1939. 

9. Earth Movement Due to German 50- and 250-Kg and 
British 250-Lb A. S. Bombs Exploded Below Ground, 
R.C. 153, Ministry of Home Security, RRL, Novem¬ 
ber 1940. 

10. Bomb Explosion Test on an Open Trench in Hard Gravel 
at Hampton Ridge, R.C. 192, Ministry of Home Security, 
RRL, January 1941. 

11. A Comparison of the Crater Dimensions and Permanent 
Earth Movements in Clay, Chalk, and Gravel Soils Due 
to the Explosion of Buried Bombs, R.C. 199, Ministry 
of Home Security, RRL, March 1941. 

12. Earth Movement Due to German 250-, 500-, 1000-Kg G.P. 
Bombs Exploded Below Ground, R.C. 259, Ministry of 
Home Security, RRL, August 1941. 

13. A Preliminary Report on Camouflets in Clay Soil, R.C. 
292, Ministry of Home Security, RRL, November 1941. 

14. Earth Movement Due to 250-Kg Bombs Exploded in Clay 
Soil, R.C. 312, Ministry of Home Security, RRL, 
November 1942. 

15. Earth Movement Due to 50-Kg Bombs Exploded at 
Different Depths in Clay Soil at Richmond Park, R.C. 328, 
Ministry of Home Security, RRL, May 1942. 

16. Earth Movements Due to Buried Standard Charges ( Ap¬ 
proximately 8.5 Lb in Wt), R.C. 416, Ministry of Home 
Security, RRL, November 1943. 

17. The Radius of Damage for Underground Services, R.C. 
290, Ministry of Home Security, Research and Experi¬ 
ments, Department, October 1941. 


227. 



BIBLIOGRAPHY 


489 


18. The Acceleration of Model Building Due to the Explosion 
of a Buried Charge, Note N ARP/366/HJHS, Ministry 
of Home Security, RRL, August 1942. 

19. A Survey of Information on the Action of Bombs Exploding 
in Earth , D. G. Christopherson, R.C. 263, Ministry of 
Home Security, Civil Defense Research Committee, 
October 1941. 

20. Preliminary Measurements of Earth Pressures and Move¬ 

ments Under Detonation, L. W. Blau, W. M. Rust, Jr., 
W. D. Mounce, and J. M. Lanse, CPPAB Interim 
Report 18, National Research Council and Humble 
Oil Company, March 1942. Div. 2-240-MI 

21. Measurements of Earth Pressures and Movements Under 
Detonations , W. D. Rust, Jr., and W. D. Mounce, CPPAB 
Interim Report 19, National Research Council and 
Humble Oil Company, September 1942. Div. 2-240-M2 

22. Mobile Oscillographic Laboratory , Curtis W. Lampson 
and Walker Bleakney, OSRD 4570, NDRC A-307, 
OEMsr-675, Service Project OD-79, PUS, January 1945. 

Div. 2-111.12-M3 

23a. Effects of Underground Explosions, Volume I, Sub¬ 
surface and Target Phenomena, Curtis W. Lampson, 
Interim Report 26, Committee on Fortification Design, 
National Research Council, June 1944. Div. 2-240-M4 

23b. Effects of Underground Explosions, Volume II, Sub¬ 
surface and Surface Phenomena, Interim Report 26, 
Committee on Fortification Design, National Research 
Council, June 1944. Div. 2-240-M5 

23c. Effects of Underground Explosions, Volume III. Result¬ 
ing Damage to Structures, David Mayer and Norman C. 
Dahl, Interim Report 26, Committee on Fortification 
Design, National Research Council, June 1944. (There 
is a misplaced decimal point in Appendix A of this 
reference.) Div. 2-240-M6 

24. The Order of Effectiveness of Various Explosives in Earth, 

Curtis W. Lampson, OSRD 5506, NDRC AES-13b, 
August 1945. Div. 2-100-MI 

25. Effects of Underground Explosions, Volume IV, Influence 

of Variations of Soil Type and Depths of Charge and Gauge, 
Curtis W. Lampson, W. M. Rust, Jr., and others, 
OSRD 6304, NDRC A-359, OEMsr-260, Service Project 
OD-03, PUS, February 1946. Div. 2-240-M8 

26. Effects of Subsurface Detonations in Earth, Part II, 

B. B. Weatherby, OSRD 3036, NDRC A-238, OEMsr- 

260, Service Projects CE-5, NO-12, and others, PUS, 
December 1943, p. 3. Div. 2-240-M3 

27. The Seismic Method of Exploration Applied to Construc¬ 
tion Projects, E. R. Shepard, September to October 1939. 

28. Terminal Ballistics and Explosive Effects, John E. 

Burchard, CPPAB, National Research Council, Oct. 1, 
1943. Div. 2-200-M2 

Chapter 4 

1. The Internal Ballistics of Gun after Shot Ejection, 
J. Corner, Ballistics Report 54, ARD. 

2. The Interior Ballistics of a Gun after Shot Ejection 
Applied to the Problem of Dust Deflector Design, R. D. 
Buhler, OSRD 5350i (OTB 12i), July 1945. Div. 2-300-MI 

3. On the Emptying of a Gun, Part /, J. J. Slade, Jr. and 

C. H. Fletcher, OSRD 5399, NDRC A-336, OEMsr-260, 
Service Projects OD-154 and OD-160, PUS, August 1945. 

Div. 2-331-M2 

4. A Study of Blast Deflectors, Clark B. Millikan, E. E. 
Sechler, and R. D. Buhler, OSRD 6316, NDRC A-351, 
OEMsr-1351, Service Projects OD-154 and OD-160, 
California Institute of Technology, October 1945. 

Div. 2-330-M3 


5. Muzzle Blast: Its Characteristics, Effects and Control, 
J. J. Slade, Jr., OSRD 6462, NDRC A-391, OEMsr-260, 
Service Projects OD-154, and OD-160, PUS, March 1946. 

Div. 2-330-M4 

6. Muzzle Blast Deflector, George T. Reynolds, OEMsr- 

260, Service Project OD-154, Report PMR-20, NDRC 
Division 2, PUS, Apr. 15, 1944. Div. 2-330-MI 

7. Reduction of Smoke and Blast Osbcuration Effect, OSRD 
5068, NDRC A-325, OEMsr-1343, Service Project OD- 
154, General Electric Company, May 1945. 

Div. 2-113-M2 

8. Study of Shock Waves by Interferometry, R. Ladenburg, 

C. C. Van Voorhis, and J. R. Winckler, OSRD 4514a, 
AES 5a, December 1944. Div. 2-100-Ml 

9. Study of Shock Waves by Interferometry, J. R. Winckler, 
C. C. Van Voorhis, H. Panofsky, and R. Ladenburg, 
OSRD 5204, NDRC A-332,' OEMsr-260, Service 
Projects NO-208, and OD-03, PUS, June 1945. 

Div. 2-120-M7 

10. Muzzle Blast Pressure Measurements, George T. Rey¬ 
nolds, OEMsr-260, Service Project OD-154, Report 
PMR-21, NDRC Division 2, PUS, Apr. 15, 1944. 

Div. 2-330-M2 

11. Interaction of Shock and Rarefaction Waves in One- 
Dimensional Motion, Richard Courant, and Kurt O. 
Friedrichs, OSRD 1567, OEMsr-944, Service Projects 
OD-03 and NO-144, Report 38.1 AMP, July 5, 1943. 

AMP-101.1-M4 

12. The Study of the Effect of Muzzle Brake Design on the 

Recoil of Guns, Part I, Frank R. Simpson and Nicol H. 
Smith, OSRD 4389, NDRC A-320, OEMsr-1398, 
Service Project OD-160, The Franklin Institute, 
November 1944. Div. 2-331-MI 

13. The Effect of Muzzle Brake Design on the Recoil of Guns, 

II, Frank R. Simpson and Nicol H. Smith, OSRD 4477g, 

OTB 5g, December 1944. Div. 2-300-MI 

14. The Effect of Muzzle Brake Design on the Recoil of Guns, 

III, Frank R. Simpson and Nicol H. Smith, OSRD 

4829g, OTB 8b, March 1945. Div. 2-300-MI 

15. The Effect of Muzzle Brake Design on the Recoil of Guns, 

IV, Frank R. Simpson and Nicol H. Smith, OSRD 

4948a, OTB 9a, April 1945. Div. 2-300-MI 

16. The Effect of Muzzle Brake Design on the Recoil of Guns, V, 

Frank R. Simpson and Nicol H. Smith, OSRD 5462a, 
OTB 13a, August 1945. Div. 2-300-MI 

17. The Effect of Muzzle Brake Design on the Recoil of Guns, 
Frank R. Simpson and Nicol H. Smith, OSRD 6458, 
NDRC A-387, OEMsr-1398, Service Projects OD-160 
and OD-154, The Franklin Institute, February 1946. 

Div. 2-331-M3 

18. On Dust Raised by a Gun Blast, J. J. Slade, Jr., OSRD 

4148j, OTB 2j, September 1944. Div. 2-300-MI 

19. On Dust Raised by a Gun Blast, II, J. J. Slade, Jr., OSRD 

4477c, OTB 5c, December 1944. Div. 2-300-MI 

20. A Method for Measuring and Recording the Degree of 

Target Obscuration, R. D. Buhler, OSRD 4148h, OTB 2h, 
September 1944. Div. 2-300-MI 

21. On the Design of a Muzzle Blast Deflector, J. J. Slade, Jr., 
OSRD 4357g, OTB 4g, November 1944. Div. 2-300-MI 

22. Interior Ballistics, /, J. O. Herschfelder, R. B. Kershner, 
and C. F. Curtiss, OSRD 1236, NDRC A-142, OEMsr- 
51, Carnegie Institution of Washington. Div. 1-210.1-M2 

23. Third Report on Blast Deflectors for the Suppression of 

Dust, J. J. Slade, Jr., OSRD 4720c, OTB 7c, February 
1945. Div. 2-300-M1 

24. Fourth Report on Blast Deflectors for the Suppression of 

Dust, J. J. Slade, Jr., and C. H. Fletcher, OSRD 5094c, 
OTB 10c, May 1945. Div. 2-300-MI 


COX FIDE X TIA Lt 






490 


BIBLIOGRAPHY 


25. Shadowgraph Study of Blast with Caliber .30 Blast De¬ 
flector, R. D. Buhler, OSRD 5094f, OTB lOf, May 1945. 

Div. 2-300-Ml 

20. Equipment for Studying Muzzle Blast Effects, J. R. 
Bruman, OSRD 4077a, OTB la, August 1944. 

Div. 2-300-Ml 

27. Preliminary Report on Blast Deflectors for the Suppression 

of Dust, J. J. Slade, Jr., OSRD 4077b, OTB lb, August 
1944. Div. 2-300-Ml 

28. Reduction of Smoke and Blast Effect, S. Neal, OSRD 

4077c, OTB lc, August 1944. Div. 2-300-MI 

29. Effectiveness of Several Devices in Reducing Smoke and 

Blast Effect, E. L. Robinson and S. Neal, OSRD 4148i, 
OTB 2i, September 1944. Div. 2-300-MI 

30. Second Report on Blast Deflectors for the Suppression of 

Dust, Ray L. Kramer and J. J. Slade, Jr., OSRD 4258g, 
OTB 3g, October 1944. Div. 2-300-MI 

31. Investigation of Two New Types of Muzzle Attachments 

for Reduction of Dust Clouds, R. D. Buhler, OSRD 4258h, 
OTB 3h, October 1944. Div. 2-300-MI 

32. Effects of Variations in Design Features in Performance 

of Dust Suppressors, R. D. Buhler, OSRD 4357h, OTB 
4h, November 1944. Div. 2-300-MI 

33. Dust Suppressor Design for 37-Mm Gun, E. E. Sechler, 
OSRD 4477f, OTB 5f, December 1944. Div. 2-300-MI 

34. Effects of Height of Bore on Obscuration of Target when 

Blast Deflector is Used, R. D. Buhler, OSRD 4607b, 
OTB 6b, January 1945. Div. 2-300-MI 

35. Empirical Investigation of Multibaffle Blast Deflectors, 
R. D. Buhler, OSRD 4829a, OTB 8a, March 1945. 

Div. 2-300-Ml 

36. Digest of Reports Concerning Muzzle Brakes, H. M. 
Schwartz, OSRD 4357i, OTB 4i, November 1944. 

Div. 2-300-MI 

Chapter 6 

1. A Brief History of Tapered Bore Guns, John S. Burlew, 

NDRC A-43, OEMsr-51, Service Project OD-52, NDRC 
Division 1, Carnegie Institution of Washington, Apr. 17, 
1942. Div. 1-330-MI 

2. Stability of Subcaliber Projectiles, Charles L. Critchfield, 

NDRC A-88, OEMsr-51, Projects PA-260, OD-52, and 
NO-26, NDRC Division 1, Carnegie Institution of 
Washington, Sept. 8, 1942. Div. 1-510-MI 

3. On the Occurrence of Shatter, Milne and Hinchliffe, 
External Ballistic Department Report 30, Appendix to 
Ordnance Board Proceedings (British) 20,002. 

4. Particular reference should be made to projects of the 
Armament Research Department, England, and the 
Army Technical Development Board, Canada. 

5. High Velocity Terminal Ballistic Performance of Caliber 
.30 Armor-Piercing Mark 2 Steel Cores, Richard J. 
Emrich and C. W. Curtis, OSRD 3889, NDRC A-282, 
OEMsr-260, Projects OD-75 and P2-104, PL'S, July 1944. 

Div. 2-210-M9 

6. Subcaliber Steel Projectiles, C. W. Curtis and Richard J. 
Emrich, OSRD 4829d, NDRC OTB-Sd, March 1945. 

Div. 2-300-Ml 

7. Penetration Mechanism, III , Report 4-44, I T . S. Naval 
Proving Ground, April 1944. 

8. Tables for Computing the Mass, Center of Gravity, and 

Moments of Inertia of a Projectile with Tangent Ogival 
Nose, O. Koksharova and C. W. Curtis, OSRD 6120d, 
NDRC OTB-14d. Div. 2-300-MI 

9. The Measurement of Forces Which Resist Penetration 
of STS Armor, Mild Steel, and 2JfST Aluminum, Report 
0-2276, XL S. Naval Research Laboratory. 


10. Interim Report on the Measurement of the Deceleration of 
a Shell Penetrating Armor Plate, MOS/145/DJM, 
Ministry of Supply. 

11. An Electromagnetic Method for Measuring Projectile 
Velocity During Penetration, Richard A. Beth and E. J. 
Schaefer, OSRD 5175, NDRC A-329, OEMsr-260, 
Service Projects CE-36 and NO-12, PLLS, June 7, 1945. 

Div. 2-311-M3 

12. The Mechanics of Armor Perforation, Part I, Residual 

Velocity, H. P. Robertson, OSRD 2043, NDRC A-227, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
PUS, November 1943. (A reissue of Report A-16 with 
corrections and with an addendum by A. H. Taub and 
C. W. Curtis.) ' Div. 2-210-M7 

13. Penetration Mechanism, II, Report 3-44, V. S. Naval 
Proving Ground. 

14. A Double Pendulum for Use in Studies of the Ballistic 

Behavior of Armor, George T. Reynolds and Ray L. 
Kramer, OSRD 686, NDRC A-52, NDCrc-34, OEMsr- 
260, Service Projects CE-5, NO-11, and others, PUS, 
July 1942. ’ Div. 2-210-MI 

15. Sabot—Projectiles for Cannon, W. D. Crozier, H. F. 
Dunlap, and others, OSRD 3010, NDRC A-234, NDRC 
Division 1, University of New Mexico, December 1943. 

Div. 1-510.1-MI 

16. Free Recoil of a Target arid Its Effects on Stopping Power, 

Walker Bleakney, Interim Report 17 CPPAB, National 
Research Council, June 1942. Div. 2-522-M4 

17. Theory of A Two Dimensional Ballistic Pendulum, 

V. Rojansky, OSRD 696, NDRC A-66, NDCrc-34, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
PUS, July 1942. Div. 2-210-M2 

18. Short Base Line Projectile Velocity Measurements, 

Richard J. Emrich and L. A. Delsasso, OSRD 927, 
NDRC A-89, OEMsr-260, Service Projects CE-5, NO-11, 
and others, PUS, October 1942. Div. 2-311-MI 

19. Projectile Velocity Measurements with Light Screens and 
Spiral Chronograph, Richard J. Emrich and L. I. 
Shipman, OSRD 4948k, NDRC OTB-9k, April 1945. 

Div. 2-300-Ml 

20. Thyratron Control of a Spark Discharge Applied to: I; 
A High-Speed Chronograph; II, Multiple Spark Photog¬ 
raphy, C. A. Adams and C. A. Clemmow, Branch 
Report, RDC 8340/40, Research Department Ballistics, 
April 1941. 

21. Technique of Multiple Spark Photography Applied to 
Problems in Terminal Ballistics, H. R. Calvert and J. 
Vennart, Terminal Ballistic Report 28/44, ARD, 
December 1944. 

22. A Further Report on the Application of Mathematical 
Principles to the Design of Projectiles, Garratt and 
Bunting, Terminal Ballistics Report 89/42, ARD. 

The Performance of Composite Rigid Projectiles Contain¬ 
ing Cores of Various Weights, Garratt and Bunting, 
Terminal Ballistics Report 8/43, ARD. 

Theory of the Composite A. P. Projectile, British Ord¬ 
nance Board Proceedings, 19885. 

23. Interior Ballistics, Pai’ts I-IV, J. O. Hirschfelder, R. B. 
Kershner, and others, OSRD 1236, 1677, and U40, 
NDRC A-142, A-ISO, A-204, and A-208, OEMsr-51, 
Service Projects OD-52, NO-23, and others, Carnegie 
Institution of Washington, 1943. Div. 1-210.1-M2 
Interior Ballistics. Part V. The Performance of High- 
Velocity Guns, J. O. Hirschfelder, R. B. Kershner, and 
others, OSRD 1916, NDRC A-222, OEMsr-51, Service 
Projects OD-52, NO-23, and others, Carnegie Institu¬ 
tion of Washington, October 1943. Div. 1-210.1-M5 
Interior Ballistics. Part VI. Pressure-Travel Curves, 



BIBLIOGRAPHY 


491 


Richard E. Johnson, C. F. Curtiss, and R. B. Kershner, 
OSRD 3255, NDRC A-279, OEMsr-51, Service Projects 
OD-52, NO-23, and others, Carnegie Institution of 
Washington, June 1944. Div. 1-210.1-M7 

24. Tables for Interior Ballistics, A. A. Bennett, Ordnance 
Department Document 2039, April 1921. 

25. Resistance Functions of Various Types of Projectiles, 
Aberdeen Proving Ground, Report 27, BRL. 

20. Mechanism of A rmor Penetration, Second Partial Report, 

C. Zener and R. E. Peterson, Report 710/492, Water- 
town Arsenal, May 1943. 

27. Mechanism of Armor Penetration, First Partial Report, 

C. Zener and J. H. Holloman, Report 710/454. Water- 
town Arsenal, September 1942. 

28. A Measurement of the Redistribidion of Material in 
Armor upon Perforation, Richard J. Emrich and Ray L. 
Kramer, OSRD 4258f, NDRC OTB-3f, October 1944. 

Div. 2-300-MI 

29. Penetration Mechanism, I, Report 1-43, U. S. Naval 
Proving Ground. 

30 Penetration of Homogeneous Armor by 3-inch Flat-Nosed 
Projectiles, Report 7-43, U. S. Naval Proving Ground. 

31. Attempt of a Theory of Armor Penetration, H. A. Bethe, 
Frankford Arsenal Report, May 1941. 

32. Penetration of Armor by High Velocity Projectiles and 
Munroe Jets, R. Hill, N. F. Mott, and D. C. Pack, 
Theoretical Research Report 13/44, ARD, March 1944. 

33. Penetration of Homogeneous Plate of One Tensile Strength 
( 110,000 Psi ) by 3-In. M79 AP Projectiles: Partial 
Report, August 1944. 

34. Effect of Hardness in Plate Performance, D. G. Sopwith, 
A. F. C. Brown, and V. M. Hickson, Second Progress 
Report on the effect of scale in armor penetration 
(British), A. P. P. Coordinating Subcommittee Paper 50, 
N. P. L. Engineering Division, February 1943. 

35. Firing Trials at Normal Attack with Geometrically Similar 
Shot Against Homogeneous Armor of Varied Hardness, 
A. F. C. Brown and V. M. Hickson, Third Progress 
Report on effect of scale in armor penetration (British), 
A. P. P. Coordinating Subcommittee Paper 79, N. P. L. 
Engineering Division, September 1944. 

36. The Optimum Hardness of Homogeneous Armor for 
Resistance to Perforation at Normal Attack by Projectiles 
of Different Sizes, D. G. Sopwith, Fourth Progress Report 
on effect of scale in armor penetration (British), A. P. P. 
Coordinating Subcommittee Paper 80, N. P. L. Engi¬ 
neering Division, September 1944. 

37. The Ballistic Properties of Mild Steel at Normal Attack, 

D. G. Sopwith, A. P. P. Coordinating Subcommittee 
Paper 84, N. P. L. Engineering Division (British), 
October 1944. 

38. The Ballistic Properties of Mild Steel, Including Pre¬ 

liminary Tests of Armor Steel and Dural, OSRD 1027, 
NDRC A-lll, OEMsr-260, Service Projects CE-5, NO- 
11, and others, Ballistics Research Group, PUS, Novem¬ 
ber 1942. Div. 2-210-M4 

39. Ballistic Tests of STS Armor Plate Using 37-mm Pro¬ 
jectiles, Ralph J. Slutz, OSRD 1301, NDRC A-156, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
Ballistics Research Group, PUS, March 1943. 

Div. 2-210-M5 

40. Modified de Marre Formula—Analysis of AP Trials, 

E. A. Milne, Appendix to British Ordnance Board 
Proceedings 26,399. 

41. Perforation Limits for Nonshattering Projectile against 
Thick Homogeneous Armor at Normal Incidence, C. W. 
Curtis and Ray L. Kramer, OSRD 6464, NDRC A-393, 
OEMsr-260, Service Projects OD-75 and NO-111, PUS, 


March 1946. Div. 2-210-M10 

42. Ballistic Tests of Small Armor Plate for the Frankford 

Arsenal, George T. Reynolds, Ray L. Kramer, and 
Walker Bleakney, OSRD 689, NDRC A-67, OEMsr-260, 
Service Projects CE-5, NO-11, and others, PUS, 
July 1942. Div. 2-210-M3 

43. Ninth Partial Report on Light Armor, Report 0-1778, 
U. S. Naval Research Laboratory, September 1941. 

44. The Penetration of Homogeneous Light Armor by Jacketed 
Projectiles at Normal Obliquity, Report 14-43, U. S. 
Naval Proving Ground, July 1943. 

45. The Performance of Shot Against Plates, Report 20, 
External Ballistic Department, British Ordnance Board 
Proceedings 14981, November 1942. 

46. The Testing of Metals in Compression at High Rates of 
Strain, Frederick Seitz, Jr., OSRD 1388, NDRC A-174, 
OEMsr-825, Projects NO-11, NS-109, and P2-303, 
Carnegie Institute of Technology, April 1943. 

Div. 2-210-M6 

47. The Scale Effect in Static Penetration, G. O. Baines, 
Terminal Ballistics, (British), Report 5/45, ARD, 
July 1945. 

48. Studies of Size Effect in Heavy Class B Armor Steel, 
Progress Report, University of North Carolina, U. S. 
Naval Research Laboratory, May 1943. 

49. Second Progress Report on Size Effect in Slow Bend 
Tests of Ni-Cr Armor, Report 0-2245, U. S. Naval 
Research Laboratory. 

50. Third Progress Report on Size Effect in Slow Bend Test 
on Ni-Cr Steel, Report 0-2296, U. S. Naval Research 
Laboratory. 

51. Non-Ballistic Test for Armor Plate, Maxwell Gensamo, 

C. S. Barrett, and others, OSRD 2041, NDRC M-87, 
OEMsr-417, Projects NRC-6 and OD-84, NDRC 
Division IS, Carnegie Institute of Technology, Nov. 3, 
1943. Div. 18-201.1-MI 

52. Principles of Projectile Design for Penetration; Sixth 
Partial Report, D. M. Van Winkle, Watertown Arsenal 
Report 762/231/6, October 1944. 

53. A Statistical Study of the Shatter Velocity of Projectiles at 
Hypervelocities, Richard J. Emrich and A. M. Mood, 
OSRD 4357a, NDRC OTB-2a, September 1944. 

Div. 2-300-Ml 

54. Principles of Armor Protection: Fourth Partial Report, 
C. Zener and J. F. Sullivan, Watertown Arsenal Report 
710/607/3, June 1944. 

55. Note on Shatter of Shot at Normal Impact—Effect of 
Hardness of Plate, H. R. Calvert and J. Vennart, 
Terminal Ballistic Report 15/44, ARD, June 1944. 

56. The Performance, at High Velocity, of .55-In. AP/CR 
Tungsten Carbide Core Bullets Against I. T. 80 Plate, 
J. T. Harris, Terminal Ballistics Report 4/45, ARD, 
June 1945. 

57. Terminal Ballistics of Tungsten Carbide Projectiles: 
Mechanical Strength of Core Material, C. W. Curtis and 
Ray L. Kramer, OSRD 6465, NDRC A-394, OEMsr-260, 
Service Project OD-75, PUS, March 1946. 

Div. 2-322-MI 

58. Terminal Ballistics of Tungsten Carbide Projectiles: Body 
Failures, C. W. Curtis, OSRD 6640, NDRC A-476. 

59. Terminal Ballistics of Tungsten Carbide Projectiles: 
Length Test, C. W. Curtis, Richard J. Emrich, and Ra} r 
L. Kramer, OSRD 6466, NDRC A-395, OEMsr-260, 
Service Project OD-75, PUS, March 1946. 

Div. 2-322-M2 

60. The Effect of Nose Shape on the Ballistic Performance of 
15-Lb 3-In. AP Solid Shot Against Homogeneous Armor, 
Report 2-43, U. S. Naval Proving Ground. 


■XFIDEXTIAL 





490 


BIBLIOGRAPHY 


25. Shadowgraph Study of Blast with Caliber .30 Blast De¬ 
flector, R. D. Buhler, OSRD 5094f, OTB lOf, May 1945. 

Div. 2-300-Ml 

20. Equipment for Studying Muzzle Blast Effects, J. R. 
Bruman, OSRD 4077a, OTB la, August 1944. 

Div. 2-300-Ml 

27. Preliminary Report on Blast Deflectors for the Suppression 

of Dust, J. J. Slade, Jr., OSRD 4077b, OTB lb, August 
1944. Div. 2-300-MI 

28. Reduction of Smoke and Blast Effect, S. Neal, OSRD 

4077c, OTB lc, August 1944. Div. 2-300-MI 

29. Effectiveness of Several Devices in Reducing Smoke and 

Blast Effect, E. L. Robinson and S. Neal, OSRD 4148i, 
OTB 2i, September 1944. Div. 2-300-MI 

30. Second Report on Blast Deflectors for the Suppression of 

Dust, Ray L. Kramer and J. J. Slade, Jr., OSRD 4258g, 
OTB 3g, October 1944. Div. 2-300-M 1 

31. Investigation of Two New Types of Muzzle Attachments 

for Reduction of Dust Clouds, R. D. Buhler, OSRD 4258h, 
OTB 3h, October 1944. Div. 2-300-MI 

32. Effects of Variations in Design Features in Performance 

of Dust Suj)pressors, R. D. Buhler, OSRD 4357h, OTB 
4h, November 1944. Div. 2-300-MI 

33. Dust Suppressor Design for 37-Mm Gun, E. E. Sechler, 
OSRD 4477f, OTB 5f, December 1944. Div. 2-300-MI 

34. Effects of Height of Bore on Obscuration of Target when 

Blast Deflector is Used, R. D. Buhler, OSRD 4607b, 
OTB 6b,' January 1945. Div. 2-300-MI 

35. Empirical Investigation of Multibaffle Blast Deflectors, 
R. D. Buhler, OSRD 4829a, OTB 8a, March 1945. 

Div. 2-300-Ml 

36. Digest of Reports Concerning Muzzle Brakes, H. M. 
Schwartz, OSRD 4357i, OTB 4i, November 1944. 

Div. 2-300-M1 

Chapter 6 

1. A Brief History of Tapered Bore Guns, John S. Burlew, 

NDRC A-43, OEMsr-51, Service Project OD-52, NDRC 
Division 1, Carnegie Institution of Washington, Apr. 17, 
1942. Div. 1-330-Ml 

2. Stability of Subcaliber Projectiles, Charles L. Critchfield, 

NDRC A-88, OEMsr-51, Projects PA-260, OD-52, and 
NO-26, NDRC Division 1, Carnegie Institution of 
Washington, Sept. 8, 1942. Div. 1-510-Ml 

3. On the Occurrence of Shatter, Milne and Hinchliffe, 
External Ballistic Department Report 30, Appendix to 
Ordnance Board Proceedings (British) 20,002. 

4. Particular reference should be made to projects of the 
Armament Research Department, England, and the 
Army Technical Development Board, Canada. 

5. High Velocity Terminal Ballistic Performance of Caliber 
.30 Armor-Piercing Mark 2 Steel Cores, Richard J. 
Emrich and C. W. Curtis, OSRD 3889, NDRC A-282, 
OEMsr-260, Projects OD-75 and P2-104, PUS, July 1944. 

Div. 2-210-M9 

6. Subcaliber Steel Projectiles, C. W. Curtis and Richard J. 
Emrich, OSRD 4829d, NDRC OTB-Sd, March 1945. 

Div. 2-300-M 1 

7. Penetration Mechanism, III, Report 4-44, U. S. Naval 
Proving Ground, April 1944. 

8. Tables for Computing the Mass, Center of Gravity, and 

Moments of Inertia of a Projectile with Tangent Ogival 
Nose, O. Koksharova and C. W. Curtis, OSRD 6120d, 
NDRC OTB-14d. Div. 2-300-M 1 

9. The Measurement of Forces Which Resist Penetration 
of STS Armor, Mild Steel, and 2jST Aluminum, Report 
0-2276, U. S. Naval Research Laboratory. 


10. Interim Report on the Measurement of the Deceleration of 
a Shell Penetrating Armor Plate, MOS/145/DJM, 
Ministry of Supply. 

11. An Electromagnetic Method for Measuring Projectile 
Velocity During Penetration, Richard A. Beth and E. J. 
Schaefer, OSRD 5175, NDRC A-329, OEMsr-260, 
Service Projects CE-36 and NO-12, PUS, June 7, 1945. 

Div. 2-311-M3 

12. The Mechanics of Armor Perforation, Part I, Residual 

Velocity, H. P. Robertson, OSRD 2043, NDRC A-227, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
PUS, November 1943. (A reissue of Report A-16 with 
corrections and with an addendum hy A. H. Taub and 
C. W. Curtis.) ' Div. 2-210-M7 

13. Penetration Mechanism, II, Report 3-44, U. S. Naval 
Proving Ground. 

14. A Double Pendulum for Use in Studies of the Ballistic 

Behavior of Armor, George T. Reynolds and Ray L. 
Kramer, OSRD 686, NDRC A-52, NDCrc-34, OEMsr- 
260, Service Projects CE-5, NO-11, and others, PL T S, 
July 1942. Div. 2-210-MI 

15. Sabot—Projectiles for Cannon, W. D. Crozier, H. F. 
Dunlap, and others, OSRD 3010, NDRC A-234, NDRC 
Division 1, University of New Mexico, December 1943. 

Div. 1-510.1-MI 

16. Free Recoil of a Target and Its Effects on Stopping Power, 

Walker Bleakney, Interim Report 17 CPPAB, National 
Research Council, June 1942. Div. 2-522-M4 

17. Theory of A Two Dimensional Ballistic Pendulum, 

V. Rojansky, OSRD 696, NDRC A-66, NDCrc-34, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
PUS, July 1942. Div. 2-210-M2 

18. Short Base Line Projectile Velocity Measurements, 

Richard J. Emrich and L. A. Delsasso, OSRD 927, 
NDRC A-89, OEMsr-260, Service Projects CE-5, NO-11, 
and others, PUS, October 1942. Div. 2-311-MI 

19. Projectile Velocity Measurements with Light Screens and 
Spiral Chronograph, Richard J. Emrich and L. I. 
Shipman, OSRD 4948k, NDRC OTB-9k, April 1945. 

Div. 2-300-Ml 

20. Thyratron Control of a Spark Discharge Applied to: I; 
A High-Speed Chronograph; II, Multiple Spark Photog¬ 
raphy, C. A. Adams and C. A. Clemmow, Branch 
Report, RDC 8340/40, Research Department Ballistics, 
April 1941. 

21. Technique of Multiple Spark Photography Applied to 
Problems in Terminal Ballistics, H. R. Calvert and J. 
Vennart, Terminal Ballistic Report 28/44, ARD, 
December 1944. 

22. A Further Report on the Application of Mathematical 
Principles to the Design of Projectiles, Garratt and 
Bunting, Terminal Ballistics Report 89/42, ARD. 

The Performance of Composite Rigid Projectiles Contain¬ 
ing Cores of Various Weights, Garratt and Bunting, 
Terminal Ballistics Report 8/43, ARD. 

Theory of the Composite A. P. Projectile, British Ord¬ 
nance Board Proceedings, 19S85. 

23. Interior Ballistics, Parts I-IV, J. O. Hirschfelder, R. B. 
Kershner, and others, OSRD 1236, 1677, and D40, 
NDRC A-142, A-ISO, A-204, and A-20S, OEMsr-51, 
Service Projects OD-52, NO-23, and others, Carnegie 
Institution of Washington, 1943. Div. 1-210.1-M2 
Interior Ballistics. Part V. The Performance of High- 
Velocity Guns , J. O. Hirschfelder, R. B. Kershner, and 
others, OSRD 1916, NDRC A-222, OEMsr-51, Service 
Projects OD-52, NO-23, and others, Carnegie Institu¬ 
tion of Washington, October 1943. Div. 1-210.1-M5 
Interior Ballistics. Part ^ I. Pressure-Travel Curves, 



BIBLIOGRAPHY 


491 


Richard E. Johnson, C. F. Curtiss, and R. B. Kershner, 
OSRD 3255, NDRC A-279, OEMsr-51, Service Projects 
OD-52, NO-23, and others, Carnegie Institution of 
Washington, June 1944. Div. 1-210.1-M7 

24. Tables for Interior Ballistics, A. A. Bennett, Ordnance 
Department Document 2039, April 1921. 

25. Resistance Functions of Various Types of Projectiles, 
Aberdeen Proving Ground, Report 27, BRL. 

26. Mechanism of Armor Penetration, Second Partial Report, 

C. Zener and R. E. Peterson, Report 710/492, Water- 
town Arsenal, May 1943. 

27. Mechanism of Armor Penetration, First Partial Report, 

C. Zener and J. H. Holloman, Report 710/454. Water- 
town Arsenal, September 1942. 

28. A Measurement of the Redistribution of Material in 
Armor upon Perforation, Richard J. Emrich and Ray L. 
Kramer, OSRD 4258f, NDRC OTB-3f, October 1944. 

Div. 2-300-Ml 

29. Penetration Mechanism, J, Report 1-43, U. S. Naval 
Proving Ground. 

30 Penetration of Homogeneous Armor by 3-inch Flat-Nosed 
Projectiles, Report 7-43, U. S. Naval Proving Ground. 

31. Attempt of a Theory of Armor Penetration, H. A. Bethe, 
Frankford Arsenal Report, May 1941. 

32. Penetration of Armor by High Velocity Projectiles and 
Munroe Jets, R. Hill, N. F. Mott, and D. C. Pack, 
Theoretical Research Report 13/44, ARD, March 1944. 

33. Penetration of Homogeneous Plate of One Tensile Strength 
{110,000 Psi ) by 3-In. M79 AP Projectiles: Partial 
Report, August 1944. 

34. Effect of Hardness in Plate Performance, D. G. Sopwith, 
A. F. C. Brown, and V. M. Hickson, Second Progress 
Report on the effect of scale in armor penetration 
(British), A. P. P. Coordinating Subcommittee Paper 50, 
N. P. L. Engineering Division, February 1943. 

35. Firing Trials at Normal Attack with Geometrically Similar 
Shot Against Homogeneous Armor of Varied Hardness, 
A. F. C. Brown and V. M. Hickson, Third Progress 
Report on effect of scale in armor penetration (British), 
A. P. P. Coordinating Subcommittee Paper 79, N. P. L. 
Engineering Division, September 1944. 

36. The Optimum Hardness of Homogeneous Armor for 
Resistance to Perforation at Normal Attack by Projectiles 
of Different Sizes, D. G. Sopwith, Fourth Progress Report 
on effect of scale in armor penetration (British), A. P. P. 
Coordinating Subcommittee Paper 80, N. P. L. Engi¬ 
neering Division, September 1944. 

37. The Ballistic Properties of Mild Steel at Normal Attack, 

D. G. Sopwith, A. P. P. Coordinating Subcommittee 
Paper 84, N. P. L. Engineering Division (British), 
October 1944. 

38. The Ballistic Properties of Mild Steel, Including Pre¬ 

liminary Tests of Armor Steel and Dural, OSRD 1027, 
NDRC A-lll, OEMsr-260, Service Projects CE-5, NO- 
11, and others, Ballistics Research Group, PUS, Novem¬ 
ber 1942. Div. 2-210-M4 

39. Ballistic Tests of STS Armor Plate Using 37-mm Pro¬ 
jectiles, Ralph J. Slutz, OSRD 1301, NDRC A-156, 
OEMsr-260, Service Projects CE-5, NO-11, and others, 
Ballistics Research Group, PUS, March 1943. 

Div. 2-210-M5 

40. Modified de Marre Formula—Analysis of AP Trials, 

E. A. Milne, Appendix to British Ordnance Board 
Proceedings 26,399. 

41. Perforation Limits for Nonshattering Projectile against 
Thick Homogeneous Armor at Normal Incidence, C. W. 
Curtis and Ray L. Kramer, OSRD 6464, NDRC A-393, 
OEMsr-260, Service Projects OD-75 and NO-111, PUS, 


March 1946. Div. 2-210-M10 

42. Ballistic Tests of Small Armor Plate for the Frankford 

Arsenal, George T. Reynolds, Ray L. Kramer, and 
Walker Bleakney, OSRD 689, NDRC A-67, OEMsr-260, 
Service Projects CE-5, NO-11, and others, PUS, 
July 1942. Div. 2-210-M3 

43. Ninth Partial Report on Light Armor, Report 0-1778, 
U. S. Naval Research Laboratory, September 1941. 

44. The Penetration of Homogeneous Light Armor by Jacketed 
Projectiles at Normal Obliquity, Report 14-43, U. S. 
Naval Proving Ground, July 1943. 

45. The Performance of Shot Against Plates, Report 20, 
External Ballistic Department, British Ordnance Board 
Proceedings 14981, November 1942. 

46. The Testing of Metals in Compression at High Rates of 
Strain, Frederick Seitz, Jr., OSRD 1388, NDRC A-174, 
OEMsr-825, Projects NO-11, NS-109, and P2-303, 
Carnegie Institute of Technology, April 1943. 

Div. 2-210-M6 

47. The Scale Effect in Static Penetration, G. O. Baines, 
Terminal Ballistics, (British), Report 5/45, ARD, 
July 1945. 

4S. Studies of Size Effect in Heavy Class B Armor Steel, 
Progress Report, University of North Carolina, U. S. 
Naval Research Laboratory, May 1943. 

49. Second Progress Report on Size Effect in Slow Bend 
Tests of Ni-Cr Armor, Report 0-2245, U. S. Naval 
Research Laboratory. 

50. Third Progress Report on Size Effect in Slow Bend Test 
on Ni-Cr Steel, Report 0-2296, U. S. Naval Research 
Laboratory. 

51. Non-Ballistic Test for Armor Plate, Maxwell Gensamo, 

C. S. Barrett, and others, OSRD 2041, NDRC M-87, 
OEMsr-417, Projects NRC-6 and OD-84, NDRC 
Division 18, Carnegie Institute of Technology, Nov. 3, 
1943. Div. 18-201.1-MI 

52. Principles of Projectile Design for Penetration; Sixth 
Partial Report, D. M. Van Winkle, Watertown Arsenal 
Report 762/231/6, October 1944. 

53. A Statistical Study of the Shatter Velocity of Projectiles at 
Hypervelocities, Richard J. Emrich and A. M. Mood, 
OSRD 4357a, NDRC OTB-2a, September 1944. 

Div. 2-300-MI 

54. Principles of Armor Protection: Fourth Partial Report, 
C. Zener and J. F. Sullivan, Watertown Arsenal Report 
710/607/3, June 1944. 

55. Note on Shatter of Shot at Normal Impact—Effect of 
Hardness of Plate, H. R. Calvert and J. Vennart, 
Terminal Ballistic Report 15/44, ARD, June 1944. 

56. The Performance, at High Velocity, of .55-In. AP/CR 
Tungsten Carbide Core Bullets Against I. T. 80 Plate, 
J. T. Harris, Terminal Ballistics Report 4/45, ARD, 
June 1945. 

57. Terminal Ballistics of Tungsten Carbide Projectiles: 
Mechanical Strength of Core Material, C. W. Curtis and 
Ray L. Kramer, OSRD 6465, NDRC A-394, OEMsr-260, 
Service Project OD-75, PUS, March 1946. 

Div. 2-322-M1 

58. Terminal Ballistics of Tungsten Carbide Projectiles: Body 
Failures, C. W. Curtis, OSRD 6640, NDRC A-476. 

59. Terminal Ballistics of Tungsten Carbide Projectiles: 
Length Test, C. W. Curtis, Richard J. Emrich, and Ray 
L. Kramer, OSRD 6466, NDRC A-395, OEMsr-260, 
Service Project OD-75, PUS, March 1946. 

Div. 2-322-M2 

60. The Effect of Nose Shape on the Ballistic Performance of 
15-Lb 3-In. AP Solid Shot Against Homogeneous Armor, 
Report 2-43, U. S. Naval Proving Ground. 




492 


BIBLIOGRAPHY 


61. Terminal Ballistics of Tungsten Carbide Projectiles: 

Survey and Nose-Shape Tests, C. W. Curtis, Richard J. 
Emrich and J. Sproule, OSRD 4720b, NDRC OTB-7b, 
February 1945. Div. 2-300-MI 

62. Shatter of Caliber .80 Monobloc Steel Projectiles, Richard 

J. Emrich, OSRD 4148c, NDRC OTB-2c, September 
1944. Div. 2-300-Ml 

63. Principles of Projectile Design for Penetration: First 
Partial Report, C. Zener and R. E. Peterson, Report 
762/231, Watertown Arsenal, October 1943. 

64. Oblique Impact, with Tungsten Carbide Projectiles, C. W. 
Curtis, OSRD 4948i, NDRC OTB-9i, April 1945. 

Div. 2-300-Ml 

65. Effect of Armor-Piercing Cap on Perforation Limits, 

C. W. Curtis and Richard J. Emrich, OSRD 5094g, 
NDRC OTB-lOg, May 1945. Div. 2-300-Ml 

66. Comparison of Capped and Monobloc Steel Projectiles at 
Hypervelocities, Richard J. Emrich, J. Sproule, and C. W. 
Curtis, OSRD 4258e, NDRC OTB-3e, October 1944. 

Div. 2-300-Ml 

67. Capped Projectiles at Hypervelocities, Richard J. Emrich, 
OSRD 4077f, NDRC OTB-lf, August 1944. 

Div. 2-300-Ml 

68. Terminal Ballistics of Tungsten Carbide Projectiles: Effect 

of Carrier, Part I, E. R. Jones, C. W. Curtis, and 
Richard H. Emrich, OSRD 5350a, NDRC OTB-12a, 
July 1945. Div. 2-300-MI 

69. Terminal Ballistics of Tungsten Carbide Projectiles: Effect 

of Carrier, Part II, Richard J. Emrich, OSRD 6467, 
NDRC A-396, OEMsr-260, Service Projects OD-75 and 
NO-11, PUS, March 1946. Div. 2-322-M3 

70. British Ordnance Board Proceedings Q3369. 

71. British Ordnance Board Proceedings Q3173. 

Chapter 7 

1. Final CFD Report, John E. Burchard, National Research 

Council, December 1944, (on the program of research 
conducted by the Committee for the Corps of Engineers, 
U.S. Army, summarizing the work of the Committee on 
Fortification Design and the Committee on Passive 
Protection Against Bombing). Div. 2-530-M2 

2. Terminal Ballistics, H. P. Robertson, CPPAB, National 

Research Council, January 1941. Div. 2-200-MI 

3. Final CPPAB Report, Part I, for year ending June 1941. 

4. Penetration of Projectiles in Concrete, Richard A. Beth, 

Interim Report 3, CPPAB, National Research Council, 
November 1941. Div. 2-220-MI 

5. AP Bomb Test — Comment, Richard A. Beth, Interim 

Report 9, CPPAB, National Research Council, April 

1942. Div. 2-220-M2 

6. A Brief Summary of Recent Data on Penetration in 
Concrete at Various Scales, Richard A. Beth, Interim 
Report 18, CPPAB, National Research Council, June 

1942. Div. 2-220-M3 

7. Penetration and Explosion Tests on Concrete Slabs, 

Report I: Data, Richard A. Beth and J. Gordon Stipe, Jr., 
Interim Report 20, CPPAB, National Research Council, 
January 1943. Div. 2-220-M5 

8. Penetration and Explosion Tests on Concrete Slabs, 
Report II: Crater Profiles, J. Gordon Stipe, Jr., Interim 
Report 21, CPPAB, National Research Council, January 

1943. Div. 2-220-M6 

9. Resistance of Laminated Concrete Slabs to Perforation, 
Robert J. Hansen, Interim Memorandum M-9, CPPAB, 
National Research Council, May 1943. Div. 2-220-M7 

10. Terminal Ballistics and Explosive Effects, John E. 


Burchard, CFD, National Research Council, October 

1943. Div. 2-200-M2 

11. Concrete Properties Survey, Effect of Concrete Properties 

on Penetration Resistance, Richard A. Beth, J. Gordon 
Stipe, Jr., Marinus E. DeReus, and John T. Pittenger, 
Interim Report 27, CFD, National Research Council, 
July 1944. Div. 2-220-M11 

Concrete Properties Survey, Preparation and Physical Tests 
of Concrete, Marinus E. DeReus, Interim Report 27, 
Appendix A, CFD, National Research Council, June 30, 

1944. Div. 2-220-M12 

Concrete Properties Survey, Penetration Data, Richard A. 

Beth, J. Gordon Stipe, Jr., and John T. Pittenger, 

Interim Report 27, Appendix B, CFD, National Research 
Council, June 30, 1944. Div. 2-220-M13 

12. Ballistics Tests on Small Concrete Slabs, J. Gordon Stipe, 

Jr., Marinus E. DeReus, John T. Pittenger, and Robert 
J. Hansen, Interim Report 28, CFD, National Research 
Council, June 30, 1944. Div. 2-220-M14 

Ballistics Tests on Small Concrete Slabs, Tables of Data, 
J. Gordon Stipe, Jr., Marinus E. DeReus, John T. 
Pittenger, and Robert J. Hansen, Interim Report 28, 
Appendix A, CFD, National Research Council, June 30, 

1944. Div. 2-220-M15 

13. Repeated Fire and Edge Fire Effects on Small Concrete 
Slabs, J. Gordon Stipe, Jr., Interim Memorandum M-12, 
CFD, National Research Council, July 1944. 

Div. 2-220-M18 

14. Composite Slabs, J. Gordon Stipe, Jr., Interim Memo¬ 

randum M-13, CFD, National Research Council, June 
30, 1944. Div. 2-220-M17 

15. Penetration Theory: Estimates of Velocity and Time 

During Penetration, Richard A. Beth, OSRD 4720, 
NDRC OTB-7, Feb. 15, 1945. Div. 2-300-MI 

16. Concrete Penetration, Richard A. Beth, OSRD 4856, 

NDRC A-319, OEMsr-260, Service Projects OD-75 

and NO-11, PUS, Mar. 20, 1945. Div. 2-220-M21 

17. An Electromagnetic Method for Measuring Projectile 
Velocity during Penetration, Richard A. Beth, and E. J. 
Schaefer, OSRD 5175, NDRC A-329, OEMsr-260, 
Service Projects CE-36, and NO-12, PUS, June 7, 1945. 

Div. 2-311-M3 

18. Penetration Theory: Separable Force Laws and the Time 

of Penetration, Richard A. Beth, OSRD 5258, NDRC 
A-333, OEMsr-260, Service Projects CE-36 and NO-12, 
PUS, June 28, 1945. Div. 2-311-M2 

19. Ballistic Tests on Concrete Slabs, Part II. Effect of Nose 

Shape, J. Gordon Stipe, Jr., OSRD 6638, NDRC A- 
112M, OEMsr-260, Service Projects OD-75, CE-36, and 
NO-11, PUS, March 1946. Div. 2-220-M23 

20. Concrete Penetration, Richard A. Beth, OSRD 6459, 

NDRC A-388, OEMsr-260, Service Projects OD-75 and 
NO-11, PUS, March 1946. Div. 2-220-M24 

21. Report on AP Projectile Tests on Large Concrete Slabs 
Conducted at Fort Cronkhite, California, U. S. Engineer 
Office, San Francisco District, May 1942. 

22. Discussion of Recent British Papers on Penetration in 

Concrete, Richard A. Beth, OEMsr-260, PUS, Oct. 6, 
1943. Div. 2-220-M9 

23. Comment on Concrete Penetration Equations, J. Gordon 

Stipe, Jr., OEMsr-260, Technical Memorandum PTM- 
23, PUS, Aug. 14, 1944. Div. 2-220-M19 

24. Remarks on Fortification Design, A. H. Taub and Walker 
Bleakney, Interim Memorandum M-10, CFD, National 
Research Council, November 1944. Div. 2-530-MI 

25. “Action and Effects of Bombs,” Part 13, Civil Protection, 
Samuely and Hamann, London, 1939. 





BIBLIOGRAPHY 


493 


20. Tests and Design of Bombproof Structures of Reinforced 
Concrete, C. A. Trexel, Bureau of Yards and Docks, 
Xavy Department, Sept. 30, 1941. 

27. AP Bomb Test, Protection Tests, Bulletin No. 3, Office of 
the Chief of Engineers, War Department. 

28. Projectile and Bomb Penetration in Concrete and Steel 
(Introduction), Information Bulletin 135, Office of the 
Chief of Engineers, Army Service Forces, Nov. 11, 1943. 

29. Bomb Tests on Building Prototype, Technical Bulletin 
TB Eng 6, War Department, Feb. 7, 1944. 

30. First Partial Report on Test of German Type Concrete 
Pillboxes, and First Report on Ordnance Program No. 5937, 
Army Ordnance Department, Aberdeen Proving Ground, 
June 7, 1943. 

Second Report on Test of German Type Concrete Pillboxes 
and Second Report on Ordnance Program No. 5937, 
Army Ordnance Department , Aberdeen Proving Ground, 
July 12, 1943. 

Third Report on Test of German Type Concrete Pillboxes 
and Third Report on Ordnance Program No. 5937, Army 
Ordnance Department, Aberdeen Proving Ground, 
Aug. 21, 1943. 

Fourth Report on Test of German Type Concrete Pillboxes 
and Fourth Report on Ordnance Program No. 5937, 
Army Ordnance Department, Aberdeen Proving Ground, 
Jan. 27, 1944. 

31. Effect of Projectiles on Concrete Pillboxes, Technical 
Bulletin TB ENG 2, War Department, December 1943. 

32. First Partial Report on Development of Fuze, Nose, 
Concrete Penetration, T-105, for Anti-concrete Projectiles, 
and First Report on Ordnance Program No. 6071, Army 
Ordnance Department, Aberdeen Proving Ground, 
Jan. 24, 1944. 

Second Report on Development of Fuze, Nose, Concrete 
Piercing, T-105 for Anti-Concrete Projectiles, and Third 
Report on Ordnance Program No. 6071, Army Ordnance 
Department, Aberdeen Proving Ground, Mar. 14, 1944. 

33. The Design of Bombproof Structures, notes reference 
R. C. 392 and Bulletin A.6, Ministry of Home Security, 
Research and Experiments Department. 

34. Estimated Penetration of AP Bombs into Concrete, ARD 
Explosives Report 72/43, Anti-Concrete Committee, 
Advisory Council on Scientific Research, Ministry of 
Supply, March 1943. 

35. Attack of Concrete, Proceedings of the Ordnance Board 
Q1378, June 22, 1943. 

36. General Formula for Penetration of Projectiles into Con¬ 
crete, Proceedings of the Ordnance Board Q2312, 
June 1944. 

37. Penetration of Projectiles into Concrete: Velocity at Any 
Point of the Path, Research and Experiments Department , 
Ministry of Home Security, June 1944, (revised Decem¬ 
ber 1944). 

38. First Interim Report on Concrete for Defense Works, 
Report for the Ministry of Supply, Note MOS/16, 
Department of Scientific and Industrial Research, RRL, 
April 1941. 

39. Second Interim Report on Concrete for Defense Works, 
Protection Against 0.303-In. Armour-Piercing Bullets, 
Report to the Ministry of Supply, Note MOS/20/ACW, 
HWWP, Department of Scientific and Industrial Re¬ 
search, RRL, July 1941. 

40. Fourth Interim Report on Concrete for Defense Works, 
the Use of Model Targets and Projectiles in Penetration 
Tests, Report to the Ministry of Supply, Note MOS/26/ 
ACW.HWWP, Department of Scientific and Industrial 
Research, RRL, October 1941. 

41. Fifth Interim Report on Concrete for Defense Works, 


Tests on Model Targets to Investigate a Proposed Design 
for Strengthening Existing Reinforced Concrete Pill-Boxes 
to Withstand 6-Pr. Attack, Report to the Ministry of 
Supply, Note MOS/44/ACW.HWWP, Department of 
Scientific and Industrial Research, RRL, December 1941. 

42. Sixth Interim Report on Concrete for Defense Works — 
Reinforced Concrete to Resist 6-Pr. Attack, Model Tests, 
Report to the Ministry of Supply, Note MOS/72/ 
CW.HWWP, Department of Scientific and Industrial 
Research, RRL, March 1942. 

43. Seventh Interim Report on Concrete for Defense Works — 
Concrete to Resist Multiple 6-Pr. Attack—Detailed Results 
of Model Tests, Report to the Ministry of Supply, 
Note MOS/84/ACW.HWWP, Department of Scientific 
and Industrial Research, RRL, April 1942. 

44. Eighth Interim Report on Concrete for Defense Works, 
Preliminary Tests to Determine the Connexion between the 
Striking Velocity oj AP Shot and Their Penetration into 
Plain Concrete, Report to the Ministry of Supply, Note 
MOS/106/ACW, RRL, May 1942. 

45. Ninth Interim Report on Concrete for Defense Works —• 
Full-Scale Targets on Reinforced Concrete Designed to 
Resist Multiple 6-Pr. Attack and Their Relation to Model 
Tests, Report to the Ministry of Supply, Note MOS/ 
107/ACW.HWWP, Department of Scientific and In¬ 
dustrial Research, RRL, May 1942. 

46. Tenth Interim Report on Concrete for Defense Works — 
Reinforced Concrete to Resist the Attack of Mortar Bombs, 
Report to the Ministry of Supply, Note MOS/109/ACW, 
Department of Scientific and Industrial Research, 
RRL, June 1942. 

47. Thirteenth Interim Report on Concrete for Defense Works, 
Summary of the Position of Experimental Work, General 
Experimented Relationships, Extra-Mural Research F. 
72/212, Note MOS/223/ACW, Anti-Concrete Committee, 
Advisory Council on Scientific Research and Technical 
Development, RRL, April 1, 1943. 

48. Fourteenth Interim Report on Concrete for Defense Works 
— Thicknesses of Reinforced Concrete Necessary to Resist 
Certain Forms of Attack, Extra-Mural Research F.72/212, 
Note M0S/224/ACW, Anti-Concrete Committee, Advi¬ 
sory Council on Scientific Research and Technical Devel¬ 
opment, RRL, April 1943. 

49. Sixteenth Interim Report on Concrete for Defense Works — 
The Penetration of Oblique Shot, Extra-Mural Research 
F.72/212, Note MOS/234/ACW, Anti-Concrete Com¬ 
mittee, Advisory Council on Scientific Research and 
Technical Development, RRL, July 1943. 

50. Seventeenth Interim Report on Concrete for Defense Works 
—The Effect of Sectional Density on the Penetration Into 
Concrete of AP Shot, and the Derivation of a General 
Penetration Formula, Extra-Mural Report F.72/212, 
Note MOS/311/ACW, Anti-Concrete Committee, Ad¬ 
visory Council on Scientific Research and Technical 
Development, RRL, February 1944. 

51 . Twentieth Interim Report on Concrete for Defense Works — 
The Penetration Characteristics of the German 15 Cm.. 
Anti-Concrete Shell, Extra-Mural Research F.72/212, 
Note MOS/363/ACW, Anti-Concrete Committee, Ad¬ 
visory Council on Scientific Research and Technical 
Development, RRL, June 1944. 

52. Twenty-First Interim Report on Concrete for Defense Works 
—Summary of Experimental Residts Obtained During 
Period May 1943 to May 1944, Extra-Mural Research 
F.72/212, Note MOS.S.355/ACW, Anti-Concrete Com¬ 
mittee, (Projectile Penetration), Advisory Council on 
Scientific Research and Technical Development, RRL, 
May 1944. 


■XKII'KX 






494 


BIBLIOGRAPHY 


53. Twenty-Second Interim Report on Concrete for Defense 
Works—Suggestions for Further Experiments on the Pene¬ 
tration of Projectiles, Extra-Mural Research F.72/212, 
Note MOS/369/AC W, Anti-Concrete Committee, Advi¬ 
sory Council on Scientific Research and Technical Devel¬ 
opment, RRL, June 1944. 

54. Contact Explosions on Concrete, Donald G. Kretsinger, 

Interim Report 29, CFD, National Research Council, 
June 30. Div. 2-220-M 16 

55. “German Hollow Charge Shells and Bombs, ” Tactical 
and Technical Trends, No. 45, Apr. 1, 1944, pp. 33-37. 

56. Summary of Tests on Breaching of Walls by Gunfire, 

A. A. Ziegler, Jr., Technical Memorandum PTM-24, 
OEMsr-260, Research Project P2-204, PLTS, May 4, 
1944. Div. 2-220-M10 

57. “German Anti-Concrete Shell,” Tactical and Technical 
Trends, No. 18, Feb. 11, 1943, p. 23. 

58. Electricity and Magnetism, Third Edition, Article 715, 
Vol. II, pp. 358-359. 

Chapter 8 

1. The Probability of Perforation of Plastic Protection by 
Caliber .30 Armor-Piercing Mark 2 Bullets, Lincoln G. 
Smith, OSRD 3231, NDRC A-246, OEMsr-260, Service 
Projects CE-5, NO-11, and others, PUS, February 1944. 

Div. 2-230-M1 

2. The Resistance of Welded Unit-Construction-Plates to 
Attack by Grenades, Mortar Bombs, and Rifle Bullets, 
Report to the Ministry of Supply MOS/121/ACW/ 
DBW., Department of Scientific and Industrial Research, 
RRL, July 1942. 

3. Armor Using Plastic and Composite Materials, OSRD 
3642, NDRC A-272, OEMsr-213, Service Projects CE-5, 
NO-11, and others, The Polaroid Corporation, May 1944. 

Div. 2-230-M2 

Chapter 9 

1. Penetration in Soils, J. Gordon Stipe, Jr., Interim Report 
30, CFD, National Research Council, July 1944. 

Div. 2-240-M7 

2. The Penetration of Projectiles into Chalk, Clay, Sand and 
Shingle, OSRD Liaison Office WA-2738-9, Report to 
the Ministry of Supply, Note MOS/359/ACW, AC-6523/ 
C152, Department of Scientific and Industrial Research, 
RRL, June 1944. 

3. Second Report on the Penetration of Projectiles into Soil, 
OSRD Liaison Office WA-4116-12, Report to the Ministry 
of Supply, Note MOS/429/ACW.HLDP.KLCF, AC- 
7889/C229, Department of Scientific and Industrial 
Research, RRL, February 1945. 

4. Composite Slabs, J. Gordon Stipe, Jr., Interim Memo¬ 

randum M-13 CFD, National Research Council, June 
30, 1944. Div. 2-220-M 17 

5. Bombs, Aircraft, OSRD Liaison Office WA-841-14C, 
Proceedings of the Ordnance Board Q 95, A.M.S./33,433, 
January 6, 1939. 

6. Penetration of Bombs and Shells (Other than Incendiary 
Bombs), OSRD Liaison Office W-127-2q, Data Compila¬ 
tion 17, Research and Experiments Branch, A.R.P. 
Department, Ministry of Home Security, 1941. 

7. Tests on Bombproof Structures, Burster Courses and 
Building Prototype, (located at Area “H,” Edgewood 
Arsenal, Maryland), U. S. Engineer Office, Baltimore, 
1941. 

8. Field Fortifications, Engineer Field Manual FM5-15, 
Table VI, War Department, 1940, p. 48. 

9. Terminal Ballistics, H. P. Robertson, CPPAB, National 


Research Council, January 1941. Div. 2-200-MI 

10. Terminal Ballistics and Explosive Efleets, John E. 
Burchard, CPPAB, National Research Council, Oct. 1, 

1943. Div. 2-200-M2 

Chapter 10 

1 . The Frangible Bullet for Use in Aerial Gunnery Training, 
P. M. Gross, OSRD 6625, NDRC A-473, Duke Uni¬ 
versity, March 1946. 

2. Deformable Projectiles for Flexible Gunnery Training, 
OSRD 1788, NDRC A-210, OEMsr-260 and OEMsr- 
1284, Research Project P2-105, PUS, and Duke 
University, BRL, September 1943. Div. 2-321-MI 

3. Characteristics of Frangible Projectiles Suitable for Flexible 
Gunnery Training, Marcus E. Hobbs and P. M. Gross, 
OSRD 4077d, OTB-ld, Duke University, August 1944. 

Div. 2-300-M1 

4. Velocity-Loss and Time-of-Flight Measurements of Fran¬ 
gible Projectiles, C. W. Curtis, Richard J. Emrich, and 
Ray L. Kramer, OSRD 4077e, OTB-le, PUS, August 

1944. . Div. 2-300-M 1 

5. Temperature Effect on the Frangible Projectile Round and 

Armor, and the Influence of Lead Characteristics on the 
Properties of the Projectile: Part I, A. J. Weith, Jr. and 
J. H. Saylor; Part II, A. J. Weith, Jr., and H. Scheraga, 
OSRD 4357b, OTB-4b, Duke University, November 
1944. Div. 2-300-M 1 

6 . The Effect of Different Molding Conditions and Accelerated 
Aging Tests on the Limit Impact Velocity of the T44 
Frangible Projectile, A. J. Weith, Jr. and J. H. Saylor, 
OSRD 4607a, OTB-6a, Duke University, January 1945. 

Div. 2-300-M 1 

7. Armor Penetration and Impact Strength of Frangible 

Projectiles, K. Jeffers, Marcus E. Hobbs, and C. Deal, 
OSRD 4148a, OTB-2a, Duke University, September 
1944. Div. 2-300-M 1 

8 . Damage Tests with Caliber .50 Frangible Projectile, 
Ray L. Kramer and C. W. Curtis, OSRD 4148b, 
OTB-ab, Princeton University, September 1944. 

Div. 2-300-M 1 

9. Armor for Use Against Frangible Projectiles and Powders 
for the Frangible Projectile Round: Part I, Marcus E. 
Hobbs, A. J. Weith, Jr. and H. Scheraga; Part II, 
A. J. Weith, Jr. and Marcus E. Hobbs, OSRD 4258a, 
OTB-3a, Duke University, October 1944. Div. 2-30C-M1 

10. The Effect of Moisture Content of DuPont No. 4^59 
Smokeless Powder on the Average Muzzle Velocity of the 
T44 Round, Marcus E. Hobbs and A. J. Weith, Jr., 
OSRD 4829c, OTB-8c, Duke University, March 1945. 

Div. 2-300-M 1 

11. Preliminary Investigation of the Muzzle Velocity of the 

T44 Projectile When Fired Through Machine-Gun Barrels 
with Different Histories, A. J. Weith, Jr. and J. H. Saylor, 
OSRD 4477b, OTB-5b, Duke University, December 
1944. Div. 3-300-M1 

12. The Effect of Projectile Diameter on the Average Muzzle 

Velocity for the T44 Projectile, A. J. Weith, Jr., J. H. 
Saylor, and Marcus E. Hobbs, OSRD 4720e, OTB-7e, 
Duke University, February 1945. Div. 2-300-M 1 

13. The Effect of Temperature on the Muzzle Velocity of 

Several Production Lots of T44 Ammunition, B. C. 
Eastham and A. J. Weith, Jr., OSRD 4948c, OTB-9c, 
Duke University, April 1945. Div. 2-300-Ml 

14. Additional Investigation of the Effect of Temperature on 
the Muzzle Velocity of the T44 Ammunition, A. J. Weith, 
Jr., OSRD 5220e, OTB-lle, Duke University, June 1945. 

Div. 2-300-M 1 



BIBLIOGRAPHY 


495 


15. A Further Investigation of the Effect of Projectile Diameter 
on the Average Muzzle Velocity of the T44 Projectile, 
B. C. Eastham and A. J. Weith, Jr., OSRD lOh, Duke 
University, May 1945. 

16. Development of the Henderson Instructor’s Turret , M. E. 

Hobbs, J. H. Saylor, and others, OSRD 5220d, OTB-lld, 
Duke University, June 1945. Div. 2-300-MI 

17. Calculated Leads for Aerial Gunners Using the API-M8 
Caliber .50 Projectile and the T44 Caliber .30 Frangible 
Projectile , H. Scheraga and Marcus E. Hobbs, OSRD 
4720d, OTB-7d, Duke University, February 1945. 

Div. 2-300-Ml 

IS. Calculated Leads for Aerial Gunners Using the API-M8 
Caliber .50 Projectile and the T44 Caliber .30 Frangible 
Projectile for Parallel Flight Case, H. A. Scheraga and 
Marcus E. Hobbs, OSRD 494Sb, OTB-9b, Duke Uni¬ 
versity, April 1944. Div. 2-300-MI 

19. Calculated Leads for Aerial Gunners Using the API-M8 
Caliber .50 Projectile and the T44- Caliber .30 Frangible 
Projectile, III, G. E. Bowden and H. A. Scheraga, 
OSRD 5350g, OTB-12g, July 1945. Div. 2-300-MI 

20. Calculated Leads for Aerial Gunners Using the API-M8 
Caliber .50 Projectile and T44 Caliber .30 Frangible 
Projectile, IV, G. E. Bowden and H. A. Scheraga, 
OSRD 5350h, OTB-12h, Duke University, July 1945. 

Div. 2-30C-M1 

21. Calculated Leads for Aerial Gunners Using the API-M8 
Caliber .50 Projectile and the T44- Caliber .30 Projectile, 
G. E. Bowden and H. A. Scheraga, OSRD 5462b, 
OTB-13b, Duke University, August 1945. Div. 2-300-MI 

22. Calculated Leads J or Aerial Gunners Using the API-M8 
Caliber .50 Projectile and the T44 Caliber .30 Frangible 
Projectile, G. E. Bowden and Marcus E. Hobbs, OSRD 
6120a, OTB-14a, Duke University, October 1945. 

Div. 2-300-Ml 

Chapter 11 

1. The Model Supersonic Wind-Tunnel Project, Allen E. 

Puckett, OSRD 3569, NDRC A-269, NDCrc-36, Projects 
OD-24, NO-3, and P2-401, California Institute of 
Technology, May 1944. Div. 2-410-M4 

Proposal and Tentative Plans for a Superspeed Wind 
Tunnel, Theodor von K&rm&n, OSRD 13, NDRC A-9, 
California Institute of Technology, July 1941. 

Div. 2-410-Ml 

The Superspeed Wind Tunnel, Theodor von K&rman, 
OSRD 14, NDRC A-10, Service Project OD-24, Cali¬ 
fornia Institute of Technology, September 1941. 

Div. 2-410-M2 

The Model Supersonic Wind Tunnel, Theodor von 
K&rm£n, OSRD 519, NDRC A-38, NDCrc-36, Service 
Project OD-24, California Institute of Technology, 
April 1942. Div. 2-410-M3 

2. “Gasdynamik,” A. Busemann, Handbuch der Experi¬ 
mental Physik, Vol. 4, Part 1, 1931. 

3. “Conversion of the Stanton 3-In. High Speed Wind 
Tunnel to the Open Jet Type,” A. Bailey and S. A. 
Wood, Proceedings of the Institute of Mechanical Engi¬ 
neers, London, Vol. 135, 1937, pp. 445-466. 

4. “Nozzles for Supersonic Flow Without Shock Fronts,” 
Ascher H. Shapiro, Journal of Applied Mechanics, 
Vol. 2, No. 2, June 1944. 

Chapter 12 

1. “Effects of Momentary Stresses in Metals,” Bertram 
Hopkinson, Proceedings of the Royal Society of London, 
Vol. 74, 1904. 


2. Zwanglose Mitteilungen des Deutsches Verbandes fiir 
Materielprufung, F. Korber, No. 8, 1926, p. 91. 

3. “The Yield Point of Mild Steel,” C. W. MacGregor, 
Transactions of the American Society of Mechanical 
Engineers, Vol. 53, 1931. 

4. “The Influence of Rate of Deformation on the Tensile 
Test with Special Reference to the Yield Point in Iron 
and Steel,” C. F. Elam, Proceedings of the Royal Society 
of London, Vol. 165, 1938, p. 568. 

5. “The Effect of the Speed of Stretching and the Rate of 
Loading in the Yielding of Mild Steel,” E. A. Davis, 
Transactions of the American Society of Mechanical 
Engineers, Vol. 60, 1938. 

6. “High Speed Tension Tests at Elevated Temperatures,” 
Parts II and III, A. Nadai and M. J. Manjoine, Trans¬ 
actions of the American Society of Mechanical Engineers, 
Vol. 63, 1941. 

7. “High Velocity Tension Impact Tests,” H. C. Mann, 
Proceedings of the American Society of Testing Materials, 
Vol. 36, 1936, p. 85. 

8. “The Influence of Impact Velocity on the Tensile 
Characteristics of Some Aircraft Metals and Alloys,” 
Donald S. Clark, Technical Note 868, National Advisory 
Committee for Aeronautics, October 1942. 

9. “Stress-Strain Relations Under TentionlmpactLoading,” 
Donald S. Clark and G. Datwyler, Proceedings of the 
American Society of Testing Materials,V ol. 38, 1938, p. 98. 

10. “Rapid Tension Tests Using the Two-Load Method,” 
Deforest, C. W. MacGregor, and Anderson, Metals 
Technology, December 1941. 

11. “Influence of Rate of Strain and Temperature on Yield 
Stresses of Mild Steel, ”M. J. Manjoine, Journal of Applied 
Mechanics, Transactions of the American Society of 
Mechanical Engineers, Vol. 66, 1944. 

12. “Uber die Fortpflanzung Ebener Luftwellen von End- 
lichen Schwingungsweite,” B. Riemann, Abhandlungen 
Gesellschaft der Wissenschajten zu Gottingen, Math-Phys., 
Vol. 8, 1860, p. 43, or Collected Works, 1876, p. 144. 

13. “Longitudinal Wave Transmission and Impact,” L. H. 
Donnell, Transactions of the American Society of Mechan¬ 
ical Engineers, Vol. 52, 1930, p. 153. 

14. On the Propagation of Plastic Deformation in Solids, 
Theodor von K&rm&n, OSRD 365, NDRC A-29, Service 
Projects CE-5 and CE-6, January 1942. Div. 2-430-MI 

15. Preliminary Experiments on the Propagation of Plastic 
Deformation, Pol E. Duwez, OSRD 380, NDRC A-33, 
Service Projects CE-5 and CE-6, February 1942. 

Div. 2-430-M2 

16. The Permanent Strain in a Uniform Bar Due to Longi¬ 

tudinal Impact, Merit P. White and LeVan Griffis, 
OSRD 742, NDRC A-71, Service Projects CE-5, NO-11, 
and others, July 1942. Div. 2-434-MI 

17. Comments on White and Griffis' Theory of the Permanent 
Strain in a Uniform Bar Due to Longitudinal Impact, 
H. F. Bohnenblust, OSRD 781, NDRC A-47M, Service 
Projects CE-5, NO-11, and others, August 1942. 

Div. 2-434-M2 

18. Propagation of Plastic Waves, A Comparison of Reports 

NDRC A-29 arid RC-329, H. F. Bohnenblust, OSRD 910, 
NDRC A-53M, OEMsr-348, Service Projects CE-5, 
NO-11, and others, California Institute of Technology, 
September 1942. Div. 2-433-MI 

19. The Plastic Wave in a Wire Extended by an Impact Load, 
G. I. Taylor, R.C.329, June 1942. 

20. A Note on von Kdrmdn’s Theory of the Propagation of 
Plastic Deformation in Solids, H. F. Bohnenblust, OSRD 
664, NDRC A-41M, OEMsr-260, Service Projects CE-5, 
NO-11, and others, PUS, June 1942. Div. 2-430-M4 


CuVI’lDKX'J’l Afi 






496 


BIBLIOGRAPHY 


21. Addendum to von Kdrmdn's Theory of the Propagation of 

Plastic Deformation in Solids, C. Zener, and J. H. 
Hollomon, OSRD 659, NDRC A-37M, Service Projects 
CE-5 and CE-6, June 1942. Div. 2-430-M3 

22. The Propagation of Plastic Waves in Tension Specimens 

of Finite Length; Theory and Methods of Integration, 
Theodor von Kdrman, H. F. Bohnenblust, and D. H. 
Hyers, OSRD 946, NDRC A-103, OEMsr-348, Service 
Projects CE-5, NO-11, and others, California Institute 
of Technology, October 1942. Div. 2-433-M2 

23. Graphical Solutions for Problems of Strain Propagation in 
Tension, H. F. Bohnenblust, Joseph V. Charyk, and 
D. H. Hyers, OSRD 1204, NDRC A-131, OEMsr-348, 
Service Projects CE-5, NO-11, and others, California 
Institute of Technology, January 1943. Div. 2-434-M6 

24. The Behavior of Longitudinal Stress Waves Near Dis¬ 

continuities in Bars of Plastic Material, LeVan Griffis, 
OSRD 1799, NDRC A-212, Projects NO-11, NS-109, 
and P2-303, September 1943. Div. 2-434-M8 

25. Discussion of Energy Measurements in Tension Impact 

Tests at the California Institute of Technology, Pol E. 
Duwez, Donald S. Clark, and D. S. Wood, OSRD 1829, 
NDRC A-217, OEMsr-348, Projects NO-11, NS-109, 
and P2-303, California Institute of Technology, Sep¬ 
tember 1943. Div. 2-432-MI 

26. Wave Propagation in a Uniform Bar Whose Stress-Strain 
Curve Is Concave Upward, Merit P. White and LeVan 
Griffis, OSRD 1302, NDRC A-152, Projects NO-11, 
NS-109, and P2-303, March 1943. Div. 2-434-M7 

27. The Force Produced by Impact of a Cylindrical Body, 
Merit P. White, OSRD 1285, NDRC A-157, Projects 
NO-11, NS-109, and P2-303, March 1943. 

Div. 2-431.22-M2 

28. The Propagation of Plastic Strain in Compression, Pol E. 
Duwez, Donald S. Clark, and H. E. Martens. OSRD 
3886, NDRC M302, OEMsr-348, Projects NS-109 and 
NRC-82, California Institute of Technology, July' 7, 1944. 

Div. 18-902.11-M6 

29. Theory, Calibration, and Use of Diaphragm Blast Meters, 
W. T. Read, OSRD 6463, NDRC A-392, OEMsr-260, 
Service Project OD-03, PITS, March 1946. 

Div. 2-1U.12-M5 

30. The Behavior of Long Beams under Impact Loading, 

Pol E. Duwez, Donald S. Clark and H. F. Bohnenblust, 
OSRD 1828, NDRC A-216, OEMsr-348, Projects NO-11, 
NS-109, and P2-303, California Institute of Technology, 
September 1943. Div. 2-420-M3 

31. The Behavior of Clamped Beams under Impact Loading, 

Pol E. Duwez, H. E. Martens and Donald S. Clark, 
OSRD 4043, NDRC M-33S, OEMsr-34S, Projects NS-109 
and NRC-82, California Institute of Technology, 
Aug. 16, 1944. Div. 18-902.13-M6 

32. Applications des Potentiels, Boussinesq, Paris, 1855. 

33. Deflection and Perforation of Steel Plates at Impact 
Velocities up to 150 Feet per Second, Pol E. Duwez, 
D. S. Wood, and Donald S. Clark, OSRD 1402, NDRC 
A-175, OEMsr-348, Projects NO-11, NS-109, and P2-303, 
California Institute of Technology', April 1943. 

Div. 2-431.11-M3 

34. On the Static and Dynamic Plastic Bending of Plates, 
D. H. Hyers, OSRD 2018, NDRC A-228, OEMsr-348, 
Projects NO-11, NS-109, and P2-303, California Insti¬ 
tute of Technology', November 1943. Div. 2-431.1-MI 

35. The Behavior of Large Plates under Impact Loading, 

Pol E. Duwez, Donald S. Clark, D. S. Wood and D. H. 
Hyers, OSRD 3292, NDRC A-254, OEMsr-348, Projects 
NO-11, NS-109, and P2-303, California Institute of 
Technology, February 1944. Div. 2-420-M5 


36. On the Propagation of the Plastic Deformation Produced 
by an Expanding Cylinder, James S. Koehler and 
Frederick Seitz, Jr., OSRD 1214, NDRC A-139, OEMsr- 
336, Service Projects CE-5, NO-11, and others, Univer¬ 
sity of Pennsylvania, January 1943. Div. 2-431.22-MI 

37. The Stress Waves Produced in a Plate by a Plane Pressure 

Pulse, James S. Koehler and Frederick Seitz, Jr., OSRD 
3230, NDRC A-245, OEMsr-825, Projects NO-11, 
NS-109, and P2-303, Carnegie Institute of Technology, 
February 1943. Div. 2-434-M9 

38. An Attempt at a Theory of Armor Penetration, H. A. 
Bet he, Ordnance Laboratory, Frankford Arsenal, 1945. 

39. A Preliminary Investigation oj the Mechanism of Pene¬ 
tration, from the Standpoint of Strain Propagation, Pol E. 
Duwez and Donald S. Clark, OSRD 3957, NDRC M-317, 
OEMsr-348, Projects NS-109 and NRC-82, California 
Institute of Technology, July 19,1944. Div. 18-902.11-M7 

40. The Plastic Properties of Metals at High Rates of Strain, 

Frederick Seitz, Jr., Andrew W. Lawson, and Park H. 
Miller, Jr., OSRD 495, NDRC A-41, OEMsr-132, 
Service Projects OD-34, CE-5, and CE-6, University 
of Pennsylvania, April 1942. Div. 2-431-Ml 

41. High-Speed Compression Testing of Copper Crusher 
Cylinders and Spheres, O. C. Simpson, E. L. Fireman, 
and James S. Koehler, OSRD 3330, NDRC A-257, 
OEMsr-825, Projects OD-57, NO-7, and P2-303, Car¬ 
negie Institute of Technology', March 1944. 

Div. 2-431.21-M2 

42. The Speed Effect in Copper Crusher Cylinders and Copper 
Spheres, Frederick Seitz, Jr., Andrew W. Lawson, and 
Park H. Miller, Jr., OSRD 619, NDRC A-63, OEMsr- 
132, Service Projects OD-34, CE-5, and others, Uni¬ 
versity of Pennsylvania, June 1942. Div. 2-431.21-MI 

43. The Testing of Metals in Compression at High Rates of 
Strain, Frederick Seitz, Jr., OSRD 1388, NDRC A-174, 
OEMsr-825, Projects NO-11, NS-109, and P2-303, 
Carnegie Institute of Technologv, April 1943. 

Div. 2-210-M6 

44. High-Speed Compression Testing of Copper Crusher 
Cylinders and Spheres, Part II, G. H. Winslow and 
W. H. Bessey, OSRD 5039, NDRC A-324, OEMsr- 
825, Service Projects OD-57, NO-7, and NS-109, 
Carnegie Institute of Technology, April 1945. 

Div. 2-431.21-M3 

45. The Set Added to Compressed Cylinders after Impact, 

E. L. Fireman, James S. Koehler, and Frederick Seitz, 
Jr., OSRD 3331, NDRC A-258, OEMsr-825, Projects 
OD-57, NO-7, and P2-301, Carnegie Institute of 
Technology', March 1944. Div. 2-431.22-M4 

46. The Propagation of Plastic Strain in Tension, Pol E. 

Duwez, D. S. Wood, and Donald S. Clark, OSRD 931, 
NDRC A-99, OEMsr-348, Service Projects CE-5, NO-11, 
and others, California Institute of Technologv, October 
1942. Div. 2-434-M3 

47. The Influence of Specimen Length on Strain Propagation 

in Tension, Pol E. Duwez, D. S. Wood, and Donald S. 
Clark, OSRD 957, NDRC A-105, OEMsr-348, Service 
Projects CE-5, NO-11, and others, California Institute 

of Technology', October 1942. Div. 2-434-M4 

48. The Effect of Stopped Impact and Reflection on the 

Propagation of Plastic Strain in Tension, Pol E. Duwez, 
D. S. Wood, Donald S. Clark, and Joseph V. Charyk, 
OSRD 9S8, NDRC A-108, OEMsr-348, Service Projects 
CE-5, NO-11 and others, California Institute of Tech¬ 
nology', November 1942. Div. 2-434-M5 

49. The Influence of Impact Velocity on the Tensile Properties 
of Plain Carbon Steels and of a Cast-Steel Armor Plate, 
Pol E. Duwez, Donald S. Clark, and D. S. Wood, 



BIBLIOGRAPHY 


497 


OSRD 1274, NDRC A-154, OEMsr-348, Projects NO-11, 
NS-109 and P2-303, California Institute of Technology, 
March 1943. Div. 2-432.1-MI 

50. Factors Influencing the Propagation of Plastic Strain in 
Long Tension Specimens, Pol E. Duwez, D. S. Wood, 
and Donald S. Clark, OSRD 1304, NDRC Report A-159, 
OEMsr-348, Projects NO-11, NS-109, and P2-303, 
California Institute of Technology, March 1943. 

Div. 2-433-M3 

51. Dynamic Tests of the Tensile Properties of SAE-1020 
Steels, Armco Iron and 17ST Aluminum Alloy, Pol E. 
Duwez, D. S. Wood, and Donald S. Clark, OSRD 1490, 
NDRC A-182, OEMsr-348, Projects NO-11, NS-109 
and P2-303, California Institute of Technology, May 

1943. Div. 2-432.1-M2 

52. The Influence of Impact Velocity on the Tensile Properties 

of Class B Armor Plate, Heat-Treated Alloy Steels, and 
Stainless Steel, Pol E. Duwez, D. S. Wood, and Donald S. 
Clark, OSRD 1641, NDRC A-195, OEMsr-348, Projects 
NO-11, NS-109, and P2-303, California Institute of 
Technology, July 1943. Div. 2-432.1-M3 

53. The Influence of Specimen Dimensions and Shape on the 
Results of Tensile Impact Tests, D. S. Wood, Pol E. 
Duwez, and Donald S. Clark, OSRD 302S, NDRC A-237, 
OEMsr-348, Projects NO-11, NS-109, and P2-303, 
California Institute of Technology, December 1943. 

Div. 2-432-M2 

54. The Influence of Velocity on the Tensile Properties of a 
Carbon Steel, Two National Emergency Steels, and a 
Manganese Steel, Donald S. Clark, Pol E. Duwez, and 
D. S. Wood, OSRD 3180, NDRC A-241, OEMsr-348, 
Projects NO-11, NS-109, and P2-303, California Insti¬ 
tute of Technology, January 1944. Div. 2-432.1-M4 

55. The Influence of Impact Velocity on the Tensile Properties 

of Four Magnesium Alloys and 2fS Aluminum Alloy, 
Donald S. Clark, Pol E. Duwez, and D. S. Wood, 
OSRD 3256, NDRC A-249, OEMsr-348, Projects NO-11, 
NS-109, and P2-303, California Institute of Technology, 
February 1944. Div. 2-432.2-MI 

56. The Influence of Impact Velocity on the Tensile Properties 
of Three Types of Ship Plate: MS, HTS, STS, Donald 
S. Clark, Pol E. Duwez, and D. S. Wood, OSRD 3420, 
NDRC A-261, OEMsr-348, Projects NO-11, NS-109, 
and P2-303, California Institute of Technology, March 

1944. Div. 2-432.1-M5 

57. Influence of Impact Velocity on the Tensile Properties of 

NE 8715, NE 9415, SAE 1045, and SAE 1090 Steels, 
Donald S. Clark, Pol E. Duwez, and D. S. Wood, 
OSRD 3695, NDRC M-257, OEMsr-348, Projects NO-11, 
NRC-82. and others, California Institute of Technology, 
May 9, 1944. Div. 18-902.12-M13 

58. Influence of Impact Velocity on the Tensile Properties of 
Furniture Steel Sheets, Pol E. Duwez, Donald S. Clark, 
and H. E. Martens, OSRD 3696, NDRC M-264, OEMsr- 
348, Projects NO-11, NRC-82, and others, California 
Institute of Technology, May 9, 1944. 

Div. 18-902.12-M12 

59. Influence of Impact Velocity on the Tensile Properties of 
Some Metals and Alloys, Pol E. Duwez and Donald S. 
Clark, OSRD 3837, NDRC M-288, OEMsr-348, Projects 
NO-11, NS-109, and NRC-82, California Institute of 
Technology, June 19, 1944. Div. 18-902.12-M14 

60. The Influence of Hardness and Type of Heat Treatment 
on the Static and Impact Tensile Properties of SAE 4340 
Steel, Pol E. Duwez, H. E. Martens, Donald S. Clark 
and D. A. Elmer, OSRD 4775, NDRC M-462, OEMsr- 
348, Projects NS-109 and NRC-82, California Institute 
of Technology, Feb. 19, 1945. Div. 18-902.12-M15 


61. Some Static and Dynamic Properties of Zamac II, Die- 

Cast Alloy in Relation to Use in Mark 140 ( HIR-3 ) Fuze, 
Donald S. Clark, Pol E. Duwez and D. S. Wood, OSRD 
3425, NDRC M-234, OEMsr-348, Projects NO-11, 
NS-109, and NRC-82, California Institute of Technology, 
Mar. 27, 1944. Div. 18-902.13-M5 

62. The Propagation of the Plastic Zone Along a Tension Bar 
of a Material Having a Well-Defined Plastic Limit, 
Julius Miklowitz, OSRD 3864, NDRC A-280, OEMsr- 
891, Projects NO-11, and P2-303, Western Electric and 
Manufacturing Company, Inc., July 1944. Div.2-433-M4 

63. The Initiation and Propagation of the Plastic Zone in a 

Mild-Steel Tension Bar, Julius Miklowitz, OSRD 4612, 
NDRC A-309, OEMsr-891, Service Project NO-11, 
Western Electric and Manufacturing Company, Inc., 
January 1945. Div. 2-433-M5 

64. Behavior of Metals Under Dynamic Conditions — Pro¬ 

gression of Yielding, Pol E. Duwez, H. E. Martens and 
Donald S. Clark, OSRD 4453, NDRC M-409, OEMsr- 
348, Project NS-109, California Institute of Technology, 
Dec. 9, 1944. Div. 18-902.11-M8 

65. The Influence of Pure Strain Rate on the Tensile Properties 

of Three Types of Ship Plate, Pol E. Duwez, H. E. 
Martens, D. A. Elmer, and Donald S. Clark, OSRD 
4773, NDRC M-459, OEMsr-348, Projects NS-109 and 
NRC-82, California Institute of Technology, Feb. 19, 

1945. Div. 18-902.15-M2 

66. The Application of Pure Strain Rate Tests to an Investiga¬ 

tion of Two 76 MM Gun Tubes, Pol E. Duwez, H. E. 
Martens, D. A. Elmer and Donald S. Clark, OSRD 
4729, NDRC M-460, OEMsr-348, Projects NS-109 and 
NRC-82, California Institute of Technology, Feb. 19, 
1945. Div. 18-902.15-MI 

67. A Preliminary Study of the Influence of Rapid Loading 

and Time at Load on the Initiation of Plastic Deformation 
in Tension, Pol E. Duwez, H. E. Martens and Donald S. 
Clark, OSRD 4621, NDRC M-450, OEMsr-348, Projects 
NS-109 and NRC-82, California Institute of Technology, 
Jan. 22, 1945 Div. 18-902.14-MI 

68. The Design of a Hydropneumatic Machine for Rapid Load 

Tensile Testing, D. A. Elmer, Donald S. Clark and 
D. H. Hyers, OSRD 4774, NDRC M-461, OEMsr-348, 
Projects NS-109 and NRC-82, California Institute of 
Technology, Feb. 19, 1945. Div. 18-902.14-M2 

Chapter 13 

1. “Recent Work in the Field of High Pressures,” Percey 
W. Bridgman, The American Scientist, Vol. 31, 1943, 
p. 29. 

2. Sixth Partial Report on Light Armor—The Dynamics of 
Armor Penetration by Light Projectiles, Report 0-1591, 
Naval Research Laboratory, February 1940. 
Measurements of Forces Which Resist Penetration of STS 
Armor, Mild Steel, and 24 ST Aluminum, Report 0-2276, 
Naval Research Laboratory, April 1944. 

3. Plastic Deformation of Steel Under High Pressure, 

Percey W. Bridgman, OSRD 919, NDRC A-95, OEMsr- 
201, Service Projects CE-5, NO-11, and others, HU, 
September 1942. Div. 2-431.11-MI 

4. Plastic Deformation of Steel Under High Pressure, 

Percey W. Bridgman, OSRD 1347, NDRC A-162, OEMsr- 
201, Projects NO-11 and P2-302, HLT, March 1943. 

Div. 2-431.11-M2 

5. Plastic Deformation of Steel Under High Pressure , 

Percey W. Bridgman, OSRD 1868, NDRC A-218, 

OEMsr-201, Projects NO-11 and P2-303, HU, September 
1943. Div. 2-431.11-M4 





498 


BIBLIOGRAPHY 


6. The Plastic Properties of Steel Under Large Strains and 

High Stresses, Percey W. Bridgman, OSRD 4256, 
NDRC A-294, OEMsr-201, Service Project NO-11, 
HU, October 1944. Div. 2-431.11-M6 

7. Distortion of an Armor-Plate Steel Under Simple Com¬ 
pressive Stress to High Strains, Percey W. Bridgman, 
OSRD 3019, NDRC A-235, OEMsr-201, Projects NO-11, 
and P2-302, HU, December 1943. Div. 2-431.11-M5 

Sa. “The Measurement of Hydrostatic Pressure to 30,000 
Kg/Cm 2 ,” Percey W. Bridgman, Proceedings of the 
American Academy of Arts and Sciences, Vol. 74, 1940, 

pp. 1-10. 

b. “The Linear Compression of Iron to 30,000 Kg/Cm 2 ,” 
Percey W. Bridgman, Proceedings of the American 
Academy of Arts and Sciences, Vol. 74, 1940, pp. 11-20. 

c. “The Compression of 46 Substances to 50,000 Kg/Cm 2 ,” 
Percey W. Bridgman, Proceedings of the American 
Academy of Arts and Sciences, Vol. 74, 1940, pp. 21-51. 

9. “The Stress Distribution at the Neck of a Tension Speci¬ 
men,” Percey W. Bridgman, Transactions of the American 
Society of Metals, Vol. 32, 1944, pp. 553-574. 

10. Effect of Prestressing in Tension on Behavior of Steel in 
Tension, Percey W. Bridgman, Experimental Report 
WAL 111/7-6, Watertown Arsenal Laboratory, June 
1944. 

11. Tension Tests on Tubes under Hydrostatic Pressure, 
Percey W. Bridgman, Experimental Report WAL 111/ 
7-4, Watertown Arsenal Laboratory, January 1944. 

12. “The Latent Energy Remaining in a Metal After Cold 
Working,” G. I. Taylor, and H. Quinney, Proceedings of 
the Royal Society of London, Vol. 143, 1933-1934, p. 323. 

Chapter 14 

1. Protection Against Shaped Charges, Emerson M. Pugh, 
OSRD 6384, NDRC A-384, OEMsr-950, Service Project 
AN-1, Carnegie Institute of Technology, February 1946. 

Div. 2-510-M4 

2. Defense Against Hollow Shaped Charges, Part /, Emerson 

M. Pugh, OSRD 3199, NDRC A-242, OEMsr-950, 
Projects AN-1 and P2-206, Carnegie Institute of Tech¬ 
nology, January 1944. Div. 2-510-MI 

3. A Theory of Target Penetration of Jets, Emerson M. 

Pugh, OSRD 3752, NDRC A-274, OEMsr-950, Projects 
AN-1 and P2-206, Carnegie Institute of Technology, 
June 1944. Div. 2-310-MI 

4. Fundamental Principles of Jet Penetration: Secondary 
Penetration in Hollow-Charge Targets, Robert J. Eichel- 
berger, OSRD 414Sg, OTB-2, September 1944. 

Div. 2-300-MI 

5. Fundamentals of Jet Penetration: Theory of Jet Penetra¬ 

tion, Emerson M. Pugh and E. L. Fireman, OSRD 
4357f, OTB-4, November 1944. Div. 2-300-MI 

6. Note on the Theory of the Munroe Effect, J. L. Tuck, 
(British), A. C. 3596. 

7. A Formulation of Mr. Tuck’s Conception of Munroe Jets, 
G. I. Taylor, (British), A. C. 3734, March 1943. 

8. Mathematical Jet Theory of Lined Hollow Charges, 
Garrett Birkhoff, Report 370, BRL, June 1943. 

9. The Mechanism of Action of Cavity Charges, George B. 
Kistiakowsky, Duncan P. MacDougall, and G. H. 
Messerly, OSRD 1338, OEMsr-202, ERL, Carnegie 
Institute of Technology, April 12, 1943. Div. 8-406-MI 

10. Penetration by Munroe Jets, R. Hill, N. F. Mott, and 
D. C. Pack, (British), A. C. 5756. 

11. Penetration of Armour by High Velocity Projectiles and 
Munroe Jets, R. Hill, N. F. Mott, and D. C. Pack, 
(.British), A. C. 6024. 


12. A Review of Certain Aspects of Research on Munroe Jets, 
D. C. Pack, Theoretical Research Survey 1/44, ARD. 

13. Remark on the Hill-Mott-Pack Theory of Penetration by 
Munroe Jets, Garrett Birkhoff, Report 497, BRL, 
October 1944. 

14. High Speed Radiographic Studies of Controlled Frag¬ 
mentation, L. B. Seely and J. C. Clark, Report 368, 
BRL, June 1943. 

15. High Speed Radiographic Studies of Controlled Frag¬ 
mentation, L. B. Seely and J. C. Clark, Report 489, 
BRL, September 1944. 

16. St udies of Shaped Charges with the Rotating Dr um Camera, 

H. A. Strecker and M. H. Hurwitz, OSRD 5615, OEMsr- 
202, Service Project AN-1, ERL, Carnegie Institute of 
Technology, Jan. 15, 1946. Div. 8-401-M5 

17. Tests of Plastic Materials, Emerson M. Pugh, Robert J. 
Eichelberger, and Robert J. Lew, OSRD 4046, NDRC 
A-288, OEMsr-950, Service Project AN-1, Carnegie 
Institute of Technology, August 1944. Div. 2-230-M3 

18. Review of Principles Involved in Protecting Armored 

Vehicles Against Shaped-Charge Weapons, Emerson M. 
Pugh, OSRD 4498, NDRC A-103M, OEMsr-950, Service 
Project AN-1, Carnegie Institute of Technology, 
December 1944. Div. 2-510-M3 

19. Protection of Armored Vehicles Against Shaped Charges: 

Static Tests of Plastic and Steel Armor Combinations, 
Emerson M. Pugh and Robert J. Eichelberger, OSRD 
4148d, OTB-2, September 1944. Div. 2-300-Ml 

20. Protection of Armored Vehicles Against Shaped Charges: 
Dynamic Tests of Plastic and Steel Armor Combinations, 
Emerson M. Pugh, OSRD 4148e, OTB-2, September 

1944. Div. 2-300-Ml 

21. Correlation Between Residual Penetration of Shaped 
Charges in Mild Steel and Percentage Perforations in 
Homoplate, Emerson M. Pugh and Robert J. Eichel¬ 
berger, OSRD 4258b, OTB-3, October]1944. Div. 2-300-Ml 

22. Protection Against Shaped Charges Afforded by Spaced 

Armor, Emerson M. Pugh and Robert J. Eichelberger, 
OSRD 4258c, OTB-3, October 1944. Div. 2-300-Ml 

23. Protection of Armored Vehicles Against Shaped Charges: 

Effect of Particle Size, Grading, and Composition upon 
Stopping Power of Lilesville Gravel Plastics, Emerson M. 
Pugh and Robert J. Eichelberger, OSRD 4357c, OTB-4, 
November 1944. Div. 2-300-Ml 

24. Fundamental Principles of Jet Penetration: Secondary 

Penetration in Hollow-Charge Targets, Emerson M. Pugh 
and Robert J. Eichelberger, OSRD 4357e, OTB-4, 
November 1944. Div. 2-300-Ml 

25. Dynamic Tests on HCR2 at Aberdeen, Emerson M. Pugh 

and Robert J. Eichelberger, OSRD 4477c, OTB-5, 
December 1944. Div. 2-300-Ml 

26. Protection of Armored Vehicles Against Shaped Charges: 
Use of Chemical Compounds, Emerson M. Pugh and 
Robert J. Eichelberger, OSRD 4829f, OTB-8, March 

1945. Div. 2-300-Ml 

27. Defense of Armored Vehicles Against Shaped Charges: 

Weights and Thicknesses of Protective Slabs, Emerson M. 
Pugh and E. Fireman, OSRD 4829g, OTB-8, March 
1945. Div. 2-300-Ml 

28. Defense of Concrete Fortifications Against Shaped Charges , 

Emerson M. Pugh and G. H. Winslow, OSRD 4148, 
OTB-2, September 1944. Div. 2-300-Ml 

29. Scaling Laws for Concrete Targets Attacked by Shaped 

Charges, Emerson M. Pugh and G. H. Winslow, OSRD 
4258d, OTB-3, October 1944. Div. 2-300-Ml 

30. Defense of Concrete Fortifications Against Shaped Charges, 

Emerson M. Pugh and G. H. Winslow, OSRD 4357d, 
OTB-4, November 1944. Div. 2-300-Ml 



BIBLIOGRAPHY 


499 


31. Fundamentals of Permeation by Jets, E. Fireman and 
Emerson M. Pugh, OSRD 4829h, OTB-S, March 1945. 

Div. 2-300-Ml 

32. Comparison of Headed and Nonheaded No. 8 Detonators 
Used in Initiating M-9A1 Shaped Charges, Robert J. 
Lew and Robert J. Eichelberger, OSRD 3715, NDRC 
A-92-M, OEMsr-950, Projects AN-1 and P2-206, Car¬ 
negie Institute of Technology, June 1944. Div. 2-510-M2 

33. Fundamental Principles of Jet Penetration: Studies of 

Control Shots, W. H. Bessey, Robert J. Eichelberger, 
A. G. Strandhagen, and Emerson M. Pugh, OSRD 
4477d, OTB-5, December 1944. Div. 2-300-MI 

Chapter 15 

1. Static Detonation Trials of Three Framed Houses at Area 

“J” Aberdeen Proving Ground, Parts I and II, John E. 
Burchard, Herbert L. Beckwith, Ernest N. Gelotte, and 
Norman C. Dahl, Interim Report 23, CPPAB, National 
Research Council, April 1943. Div. 2-521-M3 

2. Effects of Confined Blast on Brick Curtain Walls, A. H. 

Taub and J. A. Wise, OSRD 6007d, NDRC AES-14cl, 
September 1945. Div. 2-100-MI 

3. Contact Explosions on Concrete, Donald G. Kretsinger, 

Report 29, CFD, National Research Council, June 30, 
1944. Div. 2-220-M16 

4. Contact Explosions Against Concrete, I. M. Freeman, 

Donald G. Kretsinger, and A. H. Taub, OSRD 6319, 
NDRC A-354, OEMsr-260, Service Project AN-29, 
PUS, December 1945. Div. 2-220-M22 

5. Relation Between Shape of Cylindrical Charges and 
Dimensions of Craters Produced—Tests of a Flat Slab at 
Shoeburyness, (British) A. C. 5713/C89, May 1944. 

6. Nose Versus Tail Initiation of Contact Charges, Walker 
Bleakney, Donald G. Kretsinger, and A. H. Taub, 
OSRD 5506c, NDRC AES-13c, August 1945. 

Div. 2-100-Ml 

7. Unpulse Delivered to a Plane Slab by a Contact Explosion, 
Donald G. Kretsinger, Interim Memorandum M-ll 
CFD, National Research Council, June 30, 1944. 

Div. 2-210-M8 

8. Unpulse Delivered to a Plane Slab by a Contact Explosion, 
II, I. M. Freeman, Donald G. Kretsinger, and A. H. 
Taub, OSRD 5506d, NDRC AES-13d, August 1945. 

Div. 2-100-MI 

9. The Limit Design of Structures Subjected to Impidsive 
Loads, with Application to Military Structures, Merit P. 
White, OSRD 4192, NDRC A-293, Service Projects 
CE-36, NO-11, and NO-12, October 1944. Div. 2-420-M6 

10. Impact Tests of Reinforced Concrete Beams, Part I, 

Frank E. Richart and Nathan H. Newmark, OSRD 1105, 
NDRC A-125, OEMsr-318, Service Projects CE-5, 
NO-12, and others, University of Illinois, December 
1942. ‘ Div. 2-220-M4 

11. Impact Tests of Reinforced Concrete Bea?ns, Part II, 
Nathan M. Newmark and Frank E. Richart, OSRD 
1751, NDRC A-213, OEMsr-318, Projects CE-5, NO-12, 
and P2-304, University of Illinois, August 1943. 

Div. 2-220-M8 

12. Impact Tests of Reinforced Concrete Beams, Part III, 

W. H. Munse and Frank E. Richart, OSRD 4490, 
NDRC A-304, OEMsr-318, Service Projects CE-36, 
NO-11, and NO-12, University of Illinois, December 
1944. Div. 2-220-M20 

13. The Reactions of Thin Beams and Slabs to Impact, Part I, 

General Theory, H. P. Robertson and Ralph J. Slutz, 
Interim Report 13, CPPAB, National Research Council, 
June 1942. Div. 2-420-MI 


14. The Reactions of Thin Beams and Slabs to Impact Loads, 

Part II, Beams, H. P. Robertson and Ralph J. Slutz, 
Interim Report 14, CPPAB, National Research Council, 
June 1942. Div. 2-420-M2 

15. The Analysis of Elastic Structures Acted upon by Impulsive 

Loadings, John B. Wilbur, OSRD 1915, NDRC A-219, 
OEMsr-468, Service Projects CE-5, NO-12, and others, 
The Massachusetts Institute of Technology, October 
1943. Div. 2-420-M4 

16. Reactions of Simple Systems under Blast Loading, D. 

Montgomery and A. H. Taub, OSRD 5393a, NDRC 
AES-12a, July 1945. Div. 2-100-MI 

17. Remarks on Reactions under Blast Loading, D. Mont¬ 

gomery and A. H. Taub, OSRD 6007a, AES-14a, 
September 1945. Div. 2-100-MI 

18. A Modification of the Impulse Criterion for Blast Damage, 
D. G. Christopherson, (British), R. C. 349, September 
1942. 

19. The Impact Resistance of Reinforced Concrete Beams, 
Department of Scientific and Industrial Research 
(British) R. C. 128, July 1940. 

20. Further Tests on the Impact Resistance of Some Reinforced 
Concrete Beams, (British) R. C. 345, RRL, August 1942. 

21. Further Tests on the Impact Resistance of Some Reinforced 
Concrete Beams, (British) R. C. 369, ARP/385/LGS, 
November 1942. 

22. Further Tests on the Impact Resistance of Some Reinforced 
Concrete Units, (British) R. C. 379, ARP/398/LGS. 
The following are not referred to specifically in this 
chapter, but are pertinent to it: 

23. Fundamental Principles of Structural ARP, John E. 

Burchard, CPPAB, National Research Council, Decem¬ 
ber 1942. Div. 2-520-M6 

24. Remarks on Fortification Design, Walker Bleakney and 
A. H. Taub, Interim Memorandum M-10, CFD, 
National Research Council, November 1944. 

Div. 2-530-Ml 

25. The Failure of Diaphragms under Uniform Pressure, 
Merit P. White, OSRD 1376, NDRC A-167, Projects 
NO-11, NS-109, and P2-303, April 1943. Div. 2-431.22-M3 

26. Suggestions Based on Observations of Results of Tests at 
Edgewood Arsenal, May 21, 19/+1, Frank E. Richart and 
Nathan M. Newmark, Interim Report 1, CPPAB, 
National Research Council, August 1941. Div. 2-521-MI 

27. The Problem of Defeating an Explosive Projectile. Part I, 

Introduction. Direct Hit, CPPAB, National Research 
Council, June 30, 1941. Div. 2-520-MI 

The Problem of Defeating an Explosive Projectile. Part II, 
Nearby Hit and Collateral Questions, CCPAB, National 
Research Council, June 30, 1941. Div. 2-520-M2 

The Problem of Defeating an Explosive Projectile. Part III, 
Economics oj Structural Air Raid Protection, CCPAB, 
National Research Council, June 30, 1941. Div. 2-520-M3 
The Problem oj Defeating an Explosive Projectile. Part IV, 
Summary. Rational Design—Suggestions for Further 
Research, CCPAB, National Research Council, June 30, 

1941. Div. 2-520-M4 

28. Exploratory Tests on Underground Bursters, Donald G. 
Kretsinger and David Mayer, Interim Report 10 
CPPAB, National Research Council, May 1942. 

Div. 2-522-M1 

29. Incendiary Bomb Test, Robert J. Hansen, Interim 
Report 11, CPPAB, National Research Council, May 

1942. Div. 2-522-M2 

30. Investigation of Uplift Effect of Explosion Within a 

Building, the Design of the Test Buildings, David Mayer, 
Interim Report 12, CPPAB, National Research Council, 
May 1942. Div. 2-521-M2 




500 


BIBLIOGRAPHY 


31. Blast Reduction Effect of Trulock Screens, Curtis W. 

Lampson, Interim Report 1.5, CPPAB, National Re¬ 
search Council, June 1942. Div. 2-522-M3 

32. CPPAB Final Report (for year ending June 30, 1942), 
National Research Council, June 30, 1942. Div. 2-520-M5 

33. The Use of Bamboo for Reinforcement in Concrete, 
Norman C. Dahl, Interim Report 22, CPPAB, National 
Research Council, February 1943. Div. 2-522-M5 

34. Relative Safety oj Basements and Upper Stories of Frame 
Houses in Air Raids, Henry Scheffe, Interim Report 24 
CPPAB, National Research Council, May 1943. 

Div. 2-521-M4 

35. CPPAB Final Report, (for year ending June 30, 1943). 

National Research Council, June 30, 1943. Div. 2-520-M7 
Terminal Ballistics and Explosive Effects, John E. 
Burchard, Appendix to CPPAB Final Report for year 
ending June 30, 1943. National Research Council, Oct. 
1, 1943. Div. 2-200-M2 

36. Effects of Underground Explosions. Volume I, Subsurface 

and Target Phenomena, Curtis W. Lampson, Interim 
Report 26, CFD, National Research Council, June 30, 
1944. Div. 2-240-M4 

Effects of Underground Explosions. Volume 77, Subsurface 
and Surface Phenomena, Interim Report 26, CFD, 
National Research Council, June 30,1944. Div. 2-240-M5 
Effects of Underground Explosions. Volume III , Resulting 
Damage to Structures, David Mayer and Norman C. 
Dahl, Interim Report 26, CFD, National Research 

Council, June 30, 1944. Div. 2-240-M6 

37. Final Report on the Program of Research Conducted by the 
Committee for the Cows oj Engineers, U. S. Army, 
Summarizing the Work of the CFD and CPPAB , John E. 
Burchard, National Research Council, December 1944. 

Div. 2-530-M2 

Chapter 16 

Note: Many of the references listed below are studies of 
target vulnerability made by Division 2, based on operations 
reports and on reports on fundamental investigations of 
terminal ballistics and effects of explosions. These reports 
contain references to original sources. 

References 4, 5, 7, 8, 9, 10, 11, and 14 are reprinted together 
in reference 15. 

1. Theory of Probability, with Applications, Henry Scheffe, 
OSRD 1918, NDRC A-224, OEMsr-260, Service Projects 
CE-5, CE-6, and NO-12, PITS, February 1944. 

Div. 2-540-MI 

2. Various reports by Army Operations Analysis Sections 
should be consulted. See, for example, ORS 9th Bomber 
Command, Report 19 and 25; ORS Mediterranean Allied 
Air Forces, Report 27; ORS 9th Army Air Force, 
Report 68. 


3. Joint Target Group Memorandum MS. Joint Target 
Group, AC/AS Intelligence. 

4. MAE's Calculated from Ashley Walk Trials, OSRD 5657b, 
EWT-Cb, September 1945. 

5. Attack on Open Gun Emplacements, OSRD 5657a, EWT-6a, 
September 1945. 

6. Remarks on Fortification Design, Walker Bleakne\ and 
A. H. Taub, Interim Memorandum M-10, CFD, Na¬ 
tional Research Council, November 1944. Div. 2-530-MI 

7. Attack of Railroads, OSRD 5045d, EWT-2d, May 1945. 

8. Air Attack on Bridges, OSRD 5176j, EWT-3j, June 1945. 

9. Attack of Tunnels, OSRD 5045c, EWT-2c, May 1945. 

10. Attack on Earth Slopes, OSRD 5176i, EWT-3i, June 1945. 

11. Aerial Bombing Attacks against Aerodromes—Runways 
and Landing Grounds, OSRD 4918, EWT-lc, April 1945. 

12. Striking Power of Air-Borne Weapons, OpNav-16-Y 
A43, Air Intelligence Group, Division of Naval Intelli¬ 
gence, Office of the Chief of Naval Operation, Navy 
Department, July 1944. 

13. Effectiveness of U. S. Incendiary and High Explosive 
Bombs, OSRD 6445, NDRC A-386. 

14. Air Attack on Steel Mills, OSRD 5657d, EWT-6d, 
September 1945. 

15. Study of the Physical Vulnerability of Military Targets to 

Various Types of Aerial Bombardment, Walker Bleakney, 
OSRD 6444, NDRC A-385, OEMsr-260, Service Project 
AN-29, PUS, January 1946. Div. 2-530-M3 


Chapter 18 

1. Notes on a Course of Instruction in Bomb Damage, A 
Course Given by the Ministry of Home Security, Research 
and Experiments Department, Princes Risborough, 
England, from July 6, 1944, through Aug. 4, 1944; 
Bomb Damage; Prediction and Assessment, OpNav 
16-V A58, prepared by Air Intelligence, September 1944. 

2. Weapon Data — Fire, Impact, Explosion, (formerly Effects 
of Impact and Explosion), continuing looseleaf report bj* 
Division 2, the final edition was issued as OSRD 6053 
(see Chapter 19). 

3. Terminal Ballistic and Explosive Effects, John E. Burchard. 
Appendix to Final Report for year ending June 30, 1943, 
CPPAB, National Research Council, Oct. 1, 1943. 

Div. 2-200-M2 

4. Theory of Probability, with Applications, Henry Scheffe, 
OSRD 1918, NDRC A-224, OEMsr-260, Service Proj¬ 
ects CE-5, CE-6, and NO-12, PUS, February 1944. 

Div. 2-540-MI 

5. Fundamental Principles of Structural ARP, John E. 
Burchard, CPPAB, National Research Council, 1943. 

Div. 2-520-M6 

6. U. S. Bombs and Fuzes, Enemy Bombs and Fuzes, and 
similar publications of L T .S. Navy Disposal School were 
given to all men who received additional training there. 




OSRD APPOINTEES 


DIVISION 2 

Chiefs 

E. Bright Wilson (since June 4, 1944) 
J. E. Burchard (up to June 4, 1944) 


Officers 

II. P. Robertson, Chief Advisor 

Walter Bleakney, Deputy Chief 

Burnham Kelley, Special Assistant to the Chief 

Technical Aides 
R. J. Slutz 


II. L. Bowman 

M. P. White 

Members 

D. P. MacDougall 

W. E. Lawson 


J. Von Neumann 

John B. Armenteout 

S. A. Vincent 

Consultants 

W. D. Kennedy 

C. W. Barber 


J. G. Kirkwood 

R. A. Beth 


C. AA r . Lampson 

F. II. Bohnenblust 


R. R. Martel 

P. AY. Bridgman 


A. Nadai 

W. T. Beightman, Jr. 


Stanford Neal 

John S. Burlew 


N. M. New mark 

L. A. Brothers 


E. M. Pugh 

R. AY. Carlson 


Chester LeRoy Post 

I). S. Clark 


F. E. Richart 

R. H. Cole 


V. Rojansky 

P. C. Cross 


A. C. Ruge 

C. AA r . Curtis 


W. M. Rust 

L. A. Delsasso 


F. Seitz, Jr. 

J. W. Dunham 


L. G. Smith 

AY. M. Fife 


II. D. Smyth 

P. M. Fye 


A. W. Stephens 

N. Gelotte 


R. Stephens, Jr. 

J. AY. Greig 


A. H. Taub 

P. M. Gross 


T. VON K ARM AN 

R. J. Hansen 


B. B. Weatiierby 

M. E. IIobbs 


J. B. AATlbur 


Special Representatives a 

Norman C. Dahl 
Robert H. Dietz 
Francis R. Smith 

a These men were employees under the contract but were appointed Special Representatives in 
order that they might travel to the European Theater of Operations to represent Division 2. 


Confidential* 


501 






CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS 


Contract Number 

Name and, Address of Contractor 

Subject 

NDCrc-34 

Princeton University 

Princeton, New Jersey 

Terminal ballistics and explosive effects 

NDCrc-36 

California Institute of Technology 

Pasadena, California 

Designing, constructing, and operating a continuously 
functioning supersonic wind tunnel 

OEMsr-121 

Cornell University 

Ithaca, New York 

Theoretical investigation of explosives 

OEMsr-132 

University of Pennsylvania 

Philadelphia, Pennsylvania 

Rapid rates of strain 

OEMsr-201 

Harvard University 

Cambridge, Massachusetts 

Study of plastic properties of steel under high pressure 

OEMsr-213 

Polaroid Corporation 

Cambridge, Massachusetts 

Development and testing of plastic materials for 
military purposes 

OEMsr-260 

Princeton University 

Princeton, New Jersey 

Research on problems of terminal ballistics, penetra¬ 
tion of projectiles, and effects of impact and 
detonation 

OEMsr-318 

University of Illinois 

Urbana, Illinois 

Impact tests of concrete 

OEMsr-336 

University of Pennsylvania 

Philadelphia, Pennsylvania 

Rapid rates of strain 

OEMsr-348 

California Institute of Technology 

Pasadena, California 

Rapid rates of strain 

OEMsr-424 

Herbach and Rademan 

522 Market Street 

Philadelphia, Pennsylvania 

Construction of laboratory unit 

OEMsr-468 

The Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Engineering principles of design of fortifications and 
other structures 

OEMsr-569 

Woods Hole Oceanographic Institution 

Woods Hole, Massachusetts 

Study of characteristics and effects of explosions in 
air and underwater 

OEMsr-596 

Stanolind Oil and Gas Company 

Tulsa, Oklahoma 

Construction of piezoelectric gauges for study of 
shock waves 

OEMsr-641 

The Massachusetts Institute of Technology 
Cambridge, Massachusetts 

Studies of rapid rates of strain 

OEMsr-675 

Princeton University 

Princeton, New Jersey 

Design and construction of mobile laboratory unit 

OEMsr-751 

Cornell University 

Ithaca, New York 

Development of methods of calculating damage due 
to underwater explosions 

OEMsr-825 

Carnegie Institute of Technology 

Pittsburgh, Pennsylvania 

Impact testing of steel and other materials 

OEMsr-891 

Westinghouse Electric and Manufacturing 
Company 

East Pittsburgh, Pennsylvania 

Stress-strain characteristics of metals under dynamic 
loads 

OEMsr-950 

Carnegie Institute of Technology 

Pittsburgh, Pennsylvania 

Defense against shaped charges 

OEMsr-1284 

Duke University 

Durham, North Carolina 

Development of frangible projectile for flexible gun¬ 
nery training 

OEMsr-1343 

General Electric Company 

Schenectady, New York 

Reduction of smoke and blast effect 

OEMsr-1351 

California Institute of Technology 

Pasadena, California 

Reduction of smoke and blast effect 

OEMsr-1398 

Franklin Institute 

Philadelphia, Pennsylvania 

Fundamental design of muzzle brakes 

OEMsr-1476 

University of Illinois 

Urbana, Illinois 

Construction of model explosive storage shelters 

OEMsr-1498 

Arthur D. Little Company 

30 Memorial Drive 

Cambridge, Massachusetts 

Evaluation of relative and absolute effectiveness of 
various aerial weapons 



502 






SERVICE PROJECT NUMBERS 


The projects listed below were transmitted to the Executive Secretary, 
OSRD, from the War or Navy Department through either the War De¬ 
partment Liaison Officer for NDRC or the Office of Research and Inven¬ 
tions (formerly the Coordinator of Research and Development), Navy 
Department. 


Seroice 


Project 


Number 

Subject 


AC-73 

AN-1 

AN-23 

AN-28 

AN-29 

CE-5 

CE-6 

CE-36 

OD-Ol 

OD-03 

OD-24 

OD-57 

OD-75 


OD-79 

OD-131 

OD-145 

OD-154 

OD-160 


NO-3 

NO-7 

NO-11 

NO-12 

NO-138 

NO-144 

NO-208 

NO-223 

NO-224 

NO-237 

NO-262 

NO-263 

NO-267 

NO-283 

NS-109 

NS-145 


NS-267 


Army Projects 

Utilization of frangible projectile in flexible gunnery training. 

Study of defense against shaped charges. 

Studies of combined He-IB attack on precision targets. 

Model scale explosion studies. 

Study of physical vulnerability of military targets to various types of aerial bombardment. 

Passive defense of civil population and utilities against aerial bombing. 

Passive protection of military aircraft and airport facilities against bombing. 

Requirements for protective structures. 

Study of PTX compositions. 

Study of shock waves. 

Supersonic wind tunnel development. 

Copper pressure cylinder versus copper balls for use in chamber pressure measurements. 

Investigation of the penetration of homogeneous and face-hardened armor at striking velocities of 3,000 fpsand 
above. 

Equipment for measuring and recording blast pressures (mobile laboratory unit). 

Mine case M3A1. 

Study of bomb effectiveness. 

Reduction of smoke and blast effect. 

Fundamental design of muzzle brakes. 

Navy Projects 

Supersonic wind tunnel development. 

Copper pressure cylinder versus copper balls for use in chamber pressure measurements. 

Structural defense—testing facilities. 

Testing facilities, concrete, detonation effect—blast, earth shock, structures. 

Determination of proper booster system for large explosive charges. 

Photographic examination of shock waves in air. 

Interferometric examination of air jets. 

Investigation of explosives for use in underwater munitions. 

Theoretical investigation of explosion phenomena, Parts B, C, and D (Part A remained in Division 8). 
Determination of depth of underwater explosions from surface observations. 

Production of water waves by explosions. 

Cratering properties of explosives. 

Study of physical vulnerability of military targets to various types of aerial bombardment. 

Air-blast measurements. 

Determination of properties of materials at high rate of loading in structures subjected to shock loading. 

Systematic investigation of the nonmetallic ballistic material knowm as plastic protection for the purpose of a 
better understanding and a further development of the material. 

NDRC assistance in underwater explosion measurements on submarine models. 


CONFIDENTIAL 


503 












INDEX 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. 
For access to the index volume consult the Army or Navy Agency listed on the reverse side of the half-title page. 


Aberdeen chronograph, 234 
Aberdeen Proving Ground 
air-blast measurements, 65 
frangible bullet for gunnery train¬ 
ing, 242 

supersonic wind tunnel, 251 
terminal ballistics of concrete, 192 
Accelerometers, 118 
ADP (ammonium dihydrogen phos¬ 
phate) gauge, 51, 70 
Aerial gunnery training 

coupled instructor’s turret, 246 
frangible bullet, 242-248 
hit indicator system, 245 
recommendations, 247 
target airplanes, 245-246, 248 
Aerial torpedoes, physical character¬ 
istics, 368 

Afterburning of explosives, 66-67, SO, 
91-92 

Air-blast measurements, 69-78 
blast tube, 75-76 
gauges, 69-74 

height effect on pressure and impulse, 
418-421 

peak pressure, 77, 411 
photography of explosions, 74-75 
positive impulse, 67-68, 77-78, 412- 
413 

shock-wave velocity, 74 
side-on vs. face-on pressure, 414 
Air-blast waves 

see Shock waves in air 
Airburst explosives 
see Explosions in air 
Airburst fuze, 320-321, 329-330 
Aircraft armor, 243 

Aircraft Laboratory, Wright Field, 
245 

Aircraft mines, characteristics, 368 
Aircraft weapons, 307-308 
Alcoa 24 ST dural armor, 243 
Algas (aluminum gasoline), 94 
Aluminized explosives, 76-79 
clearance of mine fields, 106 
explosive power, 33 
Aluminum cases for bombs, 82 
Amatex, 78 
Amatol 

composition, 20, 78 
effectiveness for underground ex¬ 
plosions, 127 

in underwater weapons, 20 
properties and uses, 359 
American Time Products Company 
frangible bullet, 242 
hit indicator system in target air¬ 
planes, 246 

Ammonium dihydrogen phosphate 
gauge, 51, 70 

Amplifiers for electrical gauges, 70 
Amplitude-modulated gauges, 71-72 


Anti-concrete projectiles 

see Concrete targets, projectile pene¬ 
tration 

Anti-personnel mines, 102, 374 
Anti-tank mines, 101-102, 374 
AP 40 (German hyper velocity gun), 160 
AP bombs (armor-piercing), 307, 312, 
406-407 

penetration of reinforced concrete, 
393, 397 

physical characteristics, 364 
AP projectiles 

see Projectiles, armor-piercing 
Applied Mathematics Panel 
calibration studies of gauges, 75 
evaluation of weapons, 77 
training of operations analysts, 340 
Armor, pressure deformation 
see Steel, pressure deformation 
Armor, terminal ballistics 
see Armor perforation 
Armor for aircraft, 243 
Armor perforation, 160-190 

see also Projectiles, armor-piercing 
angle of attack, 179-184 
homogenous armor, 170 
perforation formulas, 171-176 
photography, 164-165, 167 
plate hardness, 163, 174-175 
plate suspension, 165 
plate vulnerability, 171-172, 174 
resisting forces during impact, 164-165 
shatter velocity, 177, 181 
spalling from plates, 171 
terminal ballistic coefficients, 172-174 
thickness of plate, 181-183 
Armor-piercing bombs, 307, 312, 322, 
406-407 

Armor-piercing cap, 162, 163 
prevention of shatter, 171 
Artillery weapons, 308-309 
Atomic bomb 

height of burst, 89 
peak pressure, 42, 69, 77 
soil penetration, 240 

Bakelite Corporation, frangible bullet, 
242 

Ball crusher gauge 

deformation on copper spheres, 53 
evaluation, 73 
operation, 53 

peak pressure measurement, 53, 72 
theory, 53-54 

Ballistic pendulum, 151, 166 
Ballistic studies 
armor, 160-190 
bombs, 378-390 
concrete, 191-228 
plastic protection, 229-232 
soil, 233-241 

theory of terminal ballistics, 155-159 


Bangalore torpedoes, 309, 323-324 
Baronal for explosive fillings, 78-79 
Bazooka, rocket launcher, 277-278 
Bell Aircraft Corporation, 245-246 
Blast measurements in air 
see Air-blast measurements 
Blast tube, 75-76, 84 
Blast waves in air 

see Shock waves in air 
“Blunderbus” extensions for guns, 133 
Bombing attacks, force requirements 
for damage, 317-318 

Bombs 

airburst, 64-111 
armor-piercing, 307, 312, 364 
ballistic studies, 378-390 
British, 369 

concrete-piercing, 399-400 
depth bomb, 308, 314, 368 
explosive fillings, 78, 91-93, 127, 359 
flight characteristics, 378-390 
fragmentation, 307, 314, 320-322, 
325-328, 365 
fuzes, 360-363 
German, 370-371 

GP bombs, 307, 312-317, 324-332, 
364, 449 

high explosive, 307, 315-316, 328 
incendiary, 307-308, 315-316, 320, 
329-330, 366-367, 391 
Japanese, 372-373 
LC (light case), 307, 312, 330, 364 
loading efficiency, 316-317 
proximity fuzing, 82, 86, 91 
soil penetrating, 237 
Boosters, explosive, 66 
Brakes, gun-muzzle, 142-146 
design, 143-145 
efficiency factors, 145 
M-2 brake, 133 
requirements, 144 
British research 

air-blast tests, 76-77, 87 
bombs, 369 

breaching of concrete anti-tank walls, 
212 

hypervelocity gun, 160 
materials under dynamic loads, 255 
operations analysis, 340 
plastic armor, 155, 229-232 
standard bomb, 90 
Telecon cable, 118 
underground trajectory of bombs, 
238 

Bullets for aerial gunnery training 
see T-44 frangible bullet 
Bureau of Ordnance, 27 

California Institute of Technology 
gun muzzle attachments, 134 
materials under dynamic loads, 255 
supersonic wind tunnel, 251 



505 


506 


INDEX 


Cap attachment for armor-piercing 
projectile, 162, 163, 170 
Carpet-roll torpedo, 102 
Cavitation 

effect on damaging power of ex¬ 
plosive, 42-43 

photographic experiments, 43-45, 
57-58 

Chapman-Jouguet detonation state of 
explosives, 95 

Chronograph for projectile velocity 
measurement, 234 

Composition A (explosive filling) prop¬ 
erties and uses, 359 
Composition B (explosive filling) 
composition, 78 

effectiveness for underground ex¬ 
plosions, 127 
explosive effect, 79 
open air effectiveness, 92 
properties and uses, 359 
Composition C (explosive filling) prop¬ 
erties and uses, 359 

Concrete targets, projectile penetra¬ 
tion, 191-228 

see also Fortification damage 
ballistic limits of concrete penetra¬ 
tion, 396 
bombs, 399-400 

conditions for maximum damage, 
207, 210 

contact explosions, 129, 285-288 
delayed fuzed bombs, 322 
dispersion of points of impact, 211 
explosive projectiles, 207-211 • 
mathematical formulae, 192-194, 
212-227 

nose fuze, 210-211 
perforation of target, 199, 206, 218 
projectile properties, 194, 207-209, 
217, 221-223 

quality and thickness of concrete, 
193, 201-202, 211, 290-291 
ricochet and sticking of projectile, 
198-199, 213-214, 220, 396-398 
rockets, 401 

scabbing of target, 199, 208, 214, 218, 
285-286, 291, 399 
shaped charges, 416 
striking angle and velocity of projec¬ 
tile, 191, 198, 207, 2il, 215-217, 
219-220 

time and velocity of penetration, 194, 
199, 225-226, 228 
vulnerable areas, 214-216 
Concrete targets, types 
see Fortification design 
Condenser-microphone gauge, 71-72 
Conductivity gauge, 51 
Cone-end charges, 376 
Contact explosions, 285-288 
cratering in concrete, 285-286 
impulse produced by, 287-288, 415 
scabbing of concrete, 285-286 
Copper, compression testing, 262-263 
Cornell University, study of shock 
wave properties, 40, 45 


Crater formation, destructive effect, 
324-327, 422-423 

Cyclonite (cyclomethylene trinitra- 
mine), 20 

Damage gauges, 73-74 
DBX (explosive), 78-79 
Deflectors for guns, 145-150 
control of jet, 149-150 
reduction of blast effects, 145-149 
suppression of dust, 146-149 
suppression of flash, 148 
Demolition charges, characteristics, 376 
Depth bombs, 33-35 
Mark 54; 33, 60 
physical characteristics, 368 
Destruction techniques 

see Target damage techniques 
Detonating cord, line charge, 102, 105 
Detonation wave, 66-67 
Detonator caps, 49 
Diaphragm gauges, 44-45, 54, 73-74 
Modugno gauge, 54 
paper blast meter gauge, 73 
peak pressure measurement, 54 
steel diaphragms, 54 
Dragon hose, line charge, 102 
Duke University, frangible bullet re¬ 
search, 242 

duPont de Nemours Company, fran¬ 
gible bullet research, 242 
duPont powder No. 4759; 244 
Dural armor, Reynolds, 243 

Ednatol for explosive fillings, 78-79 
Eglin Field, Florida, frangible bullet 
research, 242 

Elastic wave propagation, 256-257 
Electro-magnetic blast pressure gauge, 
118 

Euler-Robins theory, projectile pene¬ 
tration, 194, 227 
Explosions, contact, 285-288 
cratering in concrete, 286-287 
impulse produced by, 287-288 
scabbing of concrete, 285-286 
Explosions, photograph}' 

see Photography of explosions 
Explosions in air, 64-109 
see also Shock waves in air 
afterburning process, 66-67, 81, 91-92 
air-blast measurements, 69-72, 95-99 
Chapman-Jouguet detonation state, 
95 

chemical reactions of explosives, 66- 
67, 81, 91-92 

composition of explosive, 76-79 
damage, 76-77, 326, 328 
evaluation of explosives, 65, 77-80, 
86-87 

flame velocity, 74, 107 
fragmentation of bombs, 65, 314-315 
fuzes for bombs, 314-315 
gas formations, 66-67, 81 
height of burst, 86-91 
low order explosions, 307 
measuring instruments, 72-74 
model town tests, 87 


physical properties of explosives, 79- 
83, 107 

principle of similitude, 80-81 
skin effect of explosives, 81 
slow-burning explosives, 93-94 
theory, 66-69 

Explosions in enclosed rooms, 91-94 
blast impulse, 93 
effect of ventilation, 92 
effectiveness, 91-93 
high explosives, 91-93 
slow-burning explosives, 93-94 
Explosions on ground, 99-100 
Explosions under ground, 110-132 
comparison of explosives, 127 
crater formations, 112-114, 126, 127, 

313, 422-423 

damage to structures, 127-132, 285, 
297-301, 312, 321-328 
earth shock waves, 112-126, 312-313, 

424 

film recording, 118 

gas formation, 112 

measuring instruments, 118-119 

model tests, 114-116 

peak pressure and impulse, 121-122, 

425 

recommendations for future work, 
132 

soil factors, 116-117, 131 
transient and permanent effects, 117 
Explosions under water, 20-63 

see also Shock waves under water 
comparison of explosives, 32-40 
craters produced, 32 
damage produced, 41-43 
description of underwater weapon, 
19-20 

detonation process, 20-21 
effect of cavitation, 42-43 
effect of charge-weight and depth, 
44, 46-48 

gas bubble formation, 28-31, 46-48, 

314, 427 

high explosives, 20-21 
measuring instruments, 44-45, 49-56 
methods of locating source, 59-61 
noncontact explosions, 41-42 
photographic methods of analysis, 
56-59 

pressure and impulse, 42, 426 
pressure inside an explosive, 21-22, 
39-41 

research facilities, 62-63 
surface phenomena, 31-32, 59 
sympathetic detonation, 50 
Explosive D, properties and uses, 359 
Explosive fillings 
airburst explosives, 78 
bombs, 359 

underground explosives, 127 
underwater weapons, 20 
Explosives, afterburning, 66-67, SO, 
91-92 

Explosives, high 
see High explosives 
Explosives, low (propellants), 66 
Explosives, magazines, 108 




INDEX 


507 


Explosives, mine clearing 
see Mine clearing explosives 
Explosives, slow-burning 
see Slow-burning explosives 

Factory Mutual Research Corporation, 
Salex burster, 93 

Firing devices, characteristics, 375 
Flintkote Company, protective panels 
for tanks, 281 
Foilmeter gauge, 74 
Folding skirt projectile, 1SS 
Formulas 

armor perforation, 171, 175 
concrete penetration, 192-194, 216-228 
crater volume in concrete, 287 
plastic bending of a concrete beam, 
295 

prediction of bombing damage, 309- 
310 

required density of bombing, 318 
scabbing limit of concrete, 285 
soil penetration, 237 
velocity of elastic wave propagation, 
256 

Fort Pierce, Florida, mine clearing ex¬ 
plosives, 102 

Fort Worth Headquarters, AAF, Train¬ 
ing Command, frangible bullet, 
242 

Fortification damage 

see also Concrete targets, projectile 
penetration; Explosions under 
ground; Target damage tech¬ 
niques; Target vulnerability 
by AP projectiles, 393, 397, 399-400 
contact explosions, 129, 285-288 
crater formations, 197-200, 286-287, 
313 

damage criteria, 429 
damage to structural components, 
313, 430-435 

explosion after penetration, 208 
force requirement for bombing at¬ 
tack, 317-318 

impact tests on concrete, 288-292, 
296-297 

noncontact charges, 128-129 
prediction of damage, 220, 296, 315- 
316 

pressure measurements, 128 
relative effectiveness of explosives, 
288 

repeated fire effect, 193, 211-212 
tests, 127-132 
theory, 130-132, 297-301 
underground explosions, 285, 297- 
301, 322 

underground structures, 127-132,313, 
434, 444 

vulnerable areas, 214-216 
Fortification design 

aggregate size in concrete, 202 

concrete “cover”, 203 

control of scabbing, 204-205, 209, 286 

cured concrete, 201 

elastic versus plastic design, 292-300 

face mats, 203-204 


laminated concrete, 193, 206, 210 
plastic protection, 229-232 
quality of concrete, 201-202, 291 
recommendations for future work, 
294-295 

reinforced concrete, 197-199, 202- 
212, 288-292 

vulnerable area diagrams, 214 
Fragmentation bombs, 320-322, 325- 
328 

on aircraft, 327-328, 443 
on freight yards, 326 
on light guns, 321 
on light targets, 320 
on open gun emplacements, 321 
on transformer substations, 330 
personnel destruction, 320, 443 
physical characteristics, 365 
Frangible bullet 

see T-44 frangible bullet 
Frankford Arsenal, frangible bullet, 242 
Franklin Institute, muzzle brakes, 134 
Frequency-modulated gauges, 71-72 
Fuzes 

airburst, 320-321, 329, 330 
delay, 329-330, 332 
for bombs, 360-363 
for concrete piercing projectiles, 210- 
211 

for high explosive bombs, 360-363 
for mines, 374 
instantaneous, 329, 330 

Gauges for pressure measurement 
ADP, 51, 70 

ball crusher, 44, 53-54, 72-73 
calibration, 70-71, 75-76 
condenser-microphone, 71-72 
conductivity, 51 
diaphragm, 37, 44-45, 54, 73-74 
electro-magnetic, 118 
foilmeter gauge, 74 
magnetostriction, 51, 72 
Modugno, 33, 54 
paper blast meter, 73 
piezoelectric, 33, 49-51, 69-71, 118 
piston, 54-56, 72-73 
quartz, 51, 70 
recording methods, 51-52 
resistor, 51, 71-72, 75, 118 
Rochelle salt, 51, 70 
rotating drum, 73 
tourmaline, 38-39, 50-51, 69-70 
UERL gauge, 44, 72-73 
Williams gauge, 73 

General Electric Company, gun muzzle 
attachments, 134 
General purpose bombs 
see GP bombs 
German research 

anti-concrete projectiles, 210 
armor-piercing projectiles, 409 
Bazookas, 277-278 
bombs, 370-371 
hypervelocity gun, 160 
mines, 370-371 
Panzerfaust, 280, 281 
pressure-operated mines, 32 


reinforcement of fortifications, 286 
steel projectiles, 187 
V2 rocket, 309 

GP bombs (general purpose), 312-317, 
324-332 

dropped on aircraft landing grounds, 
327-328 

dropped on bridges, 325 
dropped on coke ovens, 331-332 
dropped on docks, 327 
dropped on freight yards, 326 
dropped on light factory construc¬ 
tions, 329-330 

dropped on railway track, 324 
dropped on transformer substations, 
330 

dropped on tunnels, 325 
efficiency, 316 
fragmentation, 315 
mean area of effectiveness, 326 
performance data, 449 
physical characteristics, 364 
soil penetration, 395 
Groundburst charges, 99-100 
Guillotine type machines for testing 
materials, 258 

Gulf Research and Development Com¬ 
pany 

simulated Japanese anti-boat horn 
mines, 49 

universal indicator mine, 102-103 
Gun deflectors, 145-150 
control of jet, 149-150 
reduction of blast effects, 145-149 
suppression of dust, 146-149 
suppression of flash, 148 
Gun muzzle brakes, 142-146 
design, 143-145 
efficiency factors, 145 
M-2 brake, 133 
requirements, 144 
Gunnery training 

see Aerial gunnery training 
Guns, hypervelocity 

see Projectiles, hypervelocity 
Guns, muzzle blast from 

characteristics, 135-139, 146-147 

control, 141-152 

effects, 133-134, 139-141, 146 

Harvard University, air-blast measure¬ 
ments, 65 

HBX (explosive filling) 
aircraft depth bombs, 35 
composition, 20, 78 
effectiveness for airburst explosions, 
92 

effectiveness for underground explo¬ 
sions, 127 
explosive effect, 79 
in underwater weapons, 20, 35 
properties and uses, 359 
sensitivity, 79 
HCR2 plastic armor, 280 
Heiland recording oscillograph, 141 
Hexanite, 79 
High explosives 

bomb fuzes, 360-363 


CONFIDENTIAL 






508 


INDEX 


bombs, 307 

damage to factory machinery, 328 
definition, 19 
detonation process, 20-21 
fire starting efficiency, 315-316 
in enclosed rooms, 91-93 
nitro compounds, 20 
theory of detonation, 66-67 
Hilliar piston type momentum gauge, 
54-55 

Hit indicator system in target airplanes, 
246 

Hollow charges 

see Projectiles, shaped charge 
Hopkinson law of scaling, 24, 46 
Hugoniot relations for shock waves, 
40, 95 

HVAP (hypervelocity armor-piercing 
gun), 160 

Hypervelocity projectiles, 160-162 
see also Projectiles, armor-piercing 
energy loss in flight, 169 
steel projectiles, 187 
tungsten carbide projectiles, 188-189 

Impulse in shock waves 

see Peak pressure and positive impulse 
Impulse pendulum, 285, 288 
Incendiary bombs 
aircraft loading, 391 
clusters, 315 

damage to structures, 330 
effect of target combustibility, 316 
fire starting efficiency, 315 
physical characteristics, 366-367 
use on grounded aircraft, 320 
Indicator mines, 102-103 
Infantry snake (line charge), 102, 105, 
323 

Interferometer, use in studying shock 
waves, 75, 134, 137 

Japanese anti-boat horn mines, 49 
Japanese bombs, 372-373 
Japanese steel plants, vulnerability, 
331-333 

Jessop steel armor, 243 
Jet smoke rings, 137 

Land mines, characteristics, 374 
Laredo Army Air Field, Texas, fran¬ 
gible bullet, 242 

LC bombs (light case), 307, 312, 330 
physical characteristics, 364 
Lead azide, 19, 66 

Light case bombs (LC), 307, 312, 330 
physical characteristics, 364 
Line charges, 102 

aluminized explosives, 106 
Bangalore torpedoes, 309 
clearance of minefields, 103-106 
cratering effect, 423 
definition, 100 
detonating cord, 102, 105 
dimensions and weights, 105 
Dragon hose, 102 
on wire barricades, 323 


physical characteristics, 377 
pressure and impulse-distance curves, 
103-106 

snakes, 102, 105, 309, 323-324, 377 
tank hose, 102, 105 
use against defended towns, 106 
Low explosives, 66 
“Lulu” burster, 93 

M2 muzzle brake, 133 
M2 service projectiles, 235-236 
M3 snake, 105 

Mach number, definition, 253 
Mach reflection of shock waves 

height effect on pressure and impulse, 
419-421 

interaction of shock waves, 85 
Mach stem, 68-69 
Machines for testing materials 
compression testing, 262 
for testing steel under high pressure, 
267 

guillotine type, 256, 258, 264 
pneumatic impact-testing machine, 
290 

rotary type, 256, 258, 264 
tensile testing, 264 

MAE (mean area of effectiveness), ex¬ 
plosives, 309-311 
fragmentation damage, 443 
GP bombs, 329 
Magazines for explosives, 108 
Magnetostriction pressure gauge, 51, 72 
Mark 1 hydrophone, 59 
Mark 6 depth charge, 33 
Mark 13 aerial mine, 33, 49 
Mark 54 depth bomb, 33, 60 
Massachusetts Institute of Technology, 
255 

Materials, stress-strain relation 

see Stress-strain phenomena in termi¬ 
nal ballistics 

Mean area of effectiveness of explosives, 
309-311 

fragmentation damage, 443 
GP bombs, 329 
Mercury fulminate, 19, 66 
Mine clearing explosives, 101-106 
aerial bombardment of mines, 102, 
106 

aluminized explosives, 106 
carpet-roll torpedo, 102 
comparison of point and line charges, 
106 

countermining of horn mines, 49 
detonating cord, 102 
disadvantages, 102-103 
Dragon hose, 102 
effect of mine’s depth, 103 
evaluation of, 102 

factors determining distance from 
charge, 103 

line charge blasts, 103-106 
projected line charge, 102 
skip effect, 103 
snakes, 102, 323 
tank hose, 102 


Mines 

aircraft, 368 
anti-personnel, 102, 374 
anti-tank, 101-102, 374 
damage to ships. 328 
effective countermining radius, 49 
fuzes, 374 

German, 32, 370-371 
land mine characteristics, 374 
position of underwater mines, 29 
simulated mines for tests, 102-103 
tellermine, 103 
types of mines, 101 
universal indicator mine, 102-103 
Minol (explosive filling) 
aluminum content, 79 
composition, 20, 78 
effectiveness as open air explosive, 92 
effectiveness for underground explo¬ 
sions, 127 
explosive effect, 79 
for underwater weapons, 20, 36 
in British bomb, 90 
properties and uses, 359 
Modugno gauge, 33, 54 
Monobloc projectiles, 176-187 
Munroe jet action, 35, 308 
Muzzle-blast characteristics, 135-139 
air shock, 135-137 
blast pressure, 137-139 
detonation process, 135-136 
jet characteristics, 135-139, 146-147 
muzzle glow, 137 
rarefaction front, 137-139 
Muzzle-blast control, 141-152 
blunderbus extensions, 133 
control of jet, 149-150 
deflectors, 145-150 
field attachments, 141-142 
muzzle brake, 133-134, 142-146, 151 
recommendations for future research, 
151-152 

reduction of blast effects, 145-149 
reduction of gun’s recoil energy, 139, 
142-143 

Muzzle-blast effects, 133-134, 139-141, 
146 

blast damage to structures, 139 
dust formation, 133, 140 
effect of charge weight, 139 
effect of gun tube length, 139 
effect of muzzle velocity, 133, 139 
excessive flash from gun, 133, 141 
obscuration of target, 133, 140-141, 
146 

personnel injury, 140-141 
recoil of gun, 139 
shock wave impact, 140 

Naval Ordnance Laboratory (XOL) 
ball crusher, 53-54, 72-73 
hydrophone, 59 

Nomograms for projectile penetration 
of concrete, 220 

Oblique reflection, application to air- 
burst bombs, 86-91 



INDEX 


509 


Operations analysts, 339-341 
peacetime functions, 341 
selection of men, 340 
Optical distortion method, analysis of 
shock waves, 57 

Panzerfausts (shaped charges), 2S0-281 
Paper blast meter gauge, 73 
Peak pressure and positive impulse 
charge in free air, 95-99 
comparison of charges, 100-101, 103- 
106 

definition, 67-68 
destructive effect, 77 
distance and weight of explosive, 411- 
412 

effect of atmospheric pressure, 106- 
107 

effect of charge container, 82 
effect of distance from explosive, 77, 
95-100, 114 

effect of height of bomb burst, 86-91 
effect of size of explosive, 77 
electrical methods for measuring, 69- 
72 

ground-level pressures, 99-100 
impulse factors, underground, 121- 
122, 425 

Mach reflection of shock waves, 419- 
421 

measurement for various explosives, 
79 

mechanical gauges, 72-74 
methods of estimating pressure, 38-39 
pressure factors, underground, 119- 
122, 425 

Rankine-Hugoniot equations, 83 
ratio for common explosives, 69 
relative positive impulses, 94 
underwater explosions, 426 
velocity method of measurement, 74, 
83 

Pendulum, ballistic, 151, 166 
Pendulum, impulse, 285, 288 
Pentolite, 24, 99 
composition, 78 
explosive effect, 79 
in shaped charges, 277 
properties and uses, 359 
Petn, properties and uses, 359 
Petry concrete penetration theory, 227 
Photography of armor perforation, 164- 
165, 167 

Photography of cavitation, 43-44, 57-58 
Photography of explosions 
air cover photographs, 77, 86 
flash charge photography, 56-58 
high speed motion pictures, 48, 58- 
59, 75 

interferometry, 75, 137 
light sources, 75 
optical distortion method, 57 
rotating drum camera, 75 
Schlieren technique, 75 
spark photographs, 135, 137, 167 
X-ray photographs, 179 
Picratol, 78-79, 359 


Piezoelectric gauges 
ADP, 51, 70 

auxiliary apparatus, 70-71 
calibration, 39, 50-51, 70-71 
comparison of various crystals, 51 
compressive impact measurement, 
263 

effect of gauge mounting, 70 
evaluation, 69, 71 
measurable quantities, 118 
piezoelectric substance, 69 
pressure measurements, 69-71, 118 
pyroelectric activity, 70-71 
quartz, 51, 70 
recording of signals, 71 
reliability tests, 38-39 
Rochelle salt, 51 
sensitivity of crystals, 70 
tourmaline, 50-51, 70 
Piston gauges, 54-56, 72-73 
ball crusher gauge, 72 
rotating drum gauge, 73 
split piston gauge, 73 
spring piston gauges, 72, 74 
testing of underwater explosives, 33 
wave impulse measurement, 54-55, 73 
Plane charges, 102 
Plastic armor 

see Plastic protection 
Plastic bullet 

see T-44 frangible bullet 
Plastic protection, 229-232 
comparison with steel, 230 
description of material, 229 
effect of variation of components, 
231-232 

for tank protection, 280-2S1 
penetration by projectiles, 229-231, 
402 

proportions of materials, 231 
protection against explosions, 231 
protection against shaped charges, 
280 

ricochet, 230 

specifications of components, 231 
Plastics 

definition of plastic material, 256 
elastic limit, 256 
particle velocity, 257 
propagation of waves, 257-258 
tensile impact, 257-258 
velocity of plastic waves, 257 
“Plate denting index” of explosives, 287 
PLC (projected line charge), 102 
Pneumatic impact-testing machine, 290 
Point charges, 102 

Poncelet force law of concrete penetra¬ 
tion, 192, 194, 227 
Positive phase in shock waves, 67 
Pressure measurements in shock waves 
see Peak pressure and positive impulse 
Pressure wave 
see Shock waves 

Pressure-time curve for explosions 
detonation inside a building, 91 
oscillogram, 71, 107 
piston gauges, 73 

underground wave propagation, 113 


CONFIDENTIAL 3 


Primers, explosives, 66 
Probability dip, mine detonation, 103 
Projected line charge, 102 
Projectile deformation 

comparison of steel and tungsten 
carbide, 179 

density of projectile material, 185 
effectiveness of projectile cap, 186-187 
impact conditions, 176-183 
length of projectile, 185 
nose shape of projectile, 184 
shatter velocity, 179-183 
strength of material, 183-184 
striking velocity, 179-183 
Projectile design 

capped projectiles, 1S6-187 
causes of failures, 183 
criteria for good projectile, 184 
density of material, 185 
increase in muzzle velocity, 167-169 
length of projectile, 185 
mechanical strength of material, 183- 
184 

monobloc projectiles, 1S6-187 
nose shape, 184-185 
optimum diameter, 176 
prevention of shatter, 183 
recommendations, 190 
size of core, 167 
size of projectile, 176, 185 
stability factor, 169-170 
Projectiles, armor-piercing, 160-190 
see also Armor perforation 
armor-piercing cap, 162, 186-187 
bombs, 307, 312, 322, 364, 406-407 
deceleration during impact, 164 
deformation of projectile, 176-185 
effect of weight, 176 
fortification damage, 393, 397, 399- 
400 

German, 409 

monobloc projectiles, 176-187 
muzzle energy measurement, 167-169 
non-deforming projectile, 170-176 
prediction of projectile performance, 
176 

residual energy, 164 
rupture velocity, 177 
sabot projectiles, 165, 167, 189 
shaped charges, 417 
shatter velocity, 177-179, 184 
small caliber bullets, 405 
stability factor, 169-170 
steel projectiles, 184, 189 
striking energy, 170 
tungsten carbide projectiles, 176, 184, 
188-189, 408 
uncapped, 403-409 
velocity measurement, 166-167 
Projectiles, artillery, 308-309 
Projectiles, concrete-piercing 

see Concrete targets, projectile pene¬ 
tration 

Projectiles, flight velocity measurement, 
251 

Projectiles, hypervelocity, 160-162 
see also Projectiles, armor-piercing 
effect of armor thickness, 173 






510 


INDEX 


energy loss in flight, 169 
steel projectiles, 187 
tungsten carbide projectiles, 188-189 
Projectiles, shaped charge, 277-282 
armor-piercing, 417 
Bazooka, 277-278 
cone-end charge, 376 
design, 282 

effect of sensitive nose fuze, 2S1 
Panzerfaust, 280-281 
perforation of armor, 417 
perforation of concrete, 416 
physical characteristics, 376 
protection against, 279-280 
residual penetration, 279 
tank protection against, 280-281 
theory of jet penetration, 277-280 
Projectiles, soil penetration, 233-239 
see also Soil penetrated by projectiles 
effect of projectile mass, 237 
fuzes for, 240 
GP bombs, 395 
instability, 239-240 
M2 service projectile, 235 
perforation limit velocity, 236 
recommendations for future work, 
235-236 

rocket projectiles, 237 
shape and density of projectile, 235- 
237 

shape of projectile nose, 234, 238 
striking velocity, 234-235, 237 
underground trajectory, 238 
Propellants (low explosives), 66 
Proximity fuzes, 82, 86, 91 

Quartz pressure gauge, 51, 69-70 

Rankine-Hugoniot relations, 39, 83 
Rarefaction waves in air, 67 
Rayleigh waves, underground, 113 
RDX-Composition B, 20 
Recommendations for future research 
air blast phenomena, 108-109 
fortification design, 294-295 
muzzle blast control, 151-152 
projectile design, 190 
soil penetrating projectiles, 235-236 
underground explosion, 132 
weapon effectiveness, 333 
Reddy fox charge, 377 
Reeves Sound Laboratory, 50 
Remington Arms Company, Connec¬ 
ticut, 242 
Resistor gauge 

auxiliary apparatus, 72 
evaluation, 51, 72 
measurement of strain, 75 
pressure measurement, 118, 267 
Reynolds .301 T dural armor, 243 
Richardson, properties of air, 83 
Riemann, propagation of air waves, 255 
Robins-Euler theory, penetration of 
concrete, 194, 227 
Rochelle salt gauge, 51, 69-70 
Rockets 

airborne, 308, 320 
artillery, 308 


blast pressure measurements, 107 

German V2; 309 

on armored vehicles, 323 

on locomotives, 326 

on open gun positions, 321 

on ships, 328 

penetration into concrete, 401 
penetration into soil, 237 
Rotary type machines for testing ma¬ 
terials, 264 

Rotating drum cameras, 75, 164 
Rotating drum gauge, 73 
Rupture velocity of projectiles, defini¬ 
tion, 177 

Sabot projectile, 165, 167, 189 
Salex burster, 93 

SAP bombs (semiarmor-piercing) 
description, 307 

dropped on bridge abutments, 325 
dropped on coke ovens, 331 
dropped on heavy roof construction, 
329 

dropped on tunnels, 325 
fragmentation from, 315 
targets used against, 312 
SBX (slow-burning explosives) 
see Slow-burning explosives 
Scaling of models, 23-25, 45-46, 80-81 
Schlieren optical system, 75, 251 
Schnacke Manufacturing Company, 
Indiana, 242 
Seismic wave, 121 
Shadow ratio chart, 452-453 
Shaped charge 

see Projectiles, shaped charge 
Shatter velocity of projectiles, defini¬ 
tion, 177-179 
Shock tube, 84 
Shock waves in air, 64-109 

destruction caused by, 68-69, 76-77, 
311-312 

detonation wave, 66-67 
duration, 311 

effect of distance from charge, 94-100 
explosions in enclosed areas, 91-93 
formation, 67 
incident wave, 68-69 
Mach reflection, 85-86 
oblique reflection, 84-91 
particle velocity, 67-68, 83 
peak pressure, 67, 77 
photography of explosions, 74-75 
positive impulse, 67-68, 76-77 
pressure measurement, 67-68 
propagation, 67-68, 74, 95 
recommendations for further study, 
108-109 

reflection, 68-69, 83-85 
shape, 67 
shock tube, 84 
slipstream boundary, 85 
temperature of medium, 67-68, 106- 
107 

velocity measurement, 74 
wave front, 67 

Shock waves in earth, 112-126, 312-313 
crater formation, 422-423 



damage to bridge abutments, 325 
displacement of earth, 424 
effect of soil, 114, 116 
particle acceleration and displace¬ 
ment, 122-125 

peak pressure, 112-117, 122-125, 425 
propagation of shock wave, 118-121 
reflection, 113 
shape of wave, 119 
stress-strain curve, 116 
velocity, 114, 116 
Shock waves under water, 20-63 
cavitation, 25 
cut-off time, 24-25 
damaging factors, 43-44, 314 
destruction, 48-49, 313-314 
duration, 23-24 
effect of charge shape, 57 
energy, 21, 23-24, 37, 43 
equations for parameters, 37-39 
impulse, 37 
low pressure tail, 23 
measurement of characteristics, 23 
methods of estimating peak pressure, 

38- 39 

momentum of, 22-24 
optical distortion method of analysis, 
57 

peak pressure, 22-26, 37-39, 49 
pressure decay, 21-24 
pressure measuring instruments, 49- 
56 

propagation, 20-21, 38-41 
properties, 21-25 
reflection, 24-28 
similitude principle, 23-25 
surface phenomena, 31-32 
theoretical calculation of properties, 

39- 41 

wave front, 21-22 
Similarity law of explosives, 80-81 
application, 80 
limitations, 80-81 
“skin effect,” 81 
statement of principle, 80 
Similitude principle of shock waves, 
23-25 

Slow-burning explosives (SBX), 93-94 
aluminum and gasoline mixtures, 94 
comparison with HE explosive, 94 
for sabotage devices, 93 
“Lulu” burster, 93 
pressure time oscillogram, 94 
“Salex” burster, 93 
Snakes (line charges), 102, 105, 309 
application, 323-324 
physical characteristics, 377 
Soil penetrated by projectiles, 233-239 
see also Projectiles, soil penetration 
mathematical formulae, 237 
moisture content of soil, 235 
physical properties of soil, 233 
recommendations for future work, 
235-236 

ricochet of projectile, 396-398 
sand bag experiments, 238 
sectional energy and pressure 
theories, 239 



INDEX 


511 


soil parapets, 238 

Soil penetrated by projectiles, tests, 
234-236 
clay, 236 

concrete slabs with soil covering, 236 
experimental method, 234-235 
loam, 235-236 
parapets of soil, 236 
physical characteristics of soils used, 
235 

sand, 235 
sand bags, 236 

Sound ranging, detection of underwater 
explosions, 59-60 

Spark shadowgraphs of projectiles, 178 
Sperry Gyroscope Company, 246 
Split-piston gauge, 73 
Spring piston gauge, 72, 74 
Steel, pressure deformation, 255-273 
blast damage to steel columns, 430 
critical impact velocity, 260 
ductility of steel, 269 
effect of underwater explosions, 44-49 
elastic limit velocity, 261 
flow stress, 271 
fracture, 269-270, 272 
hardness tests, 268, 272 
heat-treatments, 269 
hydrostatic stress, 267 
mechanism of deformation, 266-267 
method of measurement, 267 
orientation of specimens, effect on 
strength, 271 
plastic deformation, 45 
punching of steel, 272-273 
rate of strain, 263 
rupture, 267 
strain-hardening, 270 
stress limit, 255 
tensile tests, 264, 268 
uniaxial state of stress, 267 
Steel projectiles, 168, 184-190 

comparison of monobloc and capped 
projectiles, 187 
conventional length, 185 
hardness, 184 

hypervelocity projectile, 187 
shatter velocity, 184-185 
Strain gauge 

auxiliary apparatus, 72 
evaluation, 51, 72 
pressure measurement, 118, 267 
strain measurements, 75 
Stress-strain phenomena in terminal 
ballistics, 255-273, 292-294 
compression tests, 259-263 
critical impact velocity, 260 
critical impulse, 260-261 
critical tensile velocity, 258 
deformation of steel under pressure, 
266-273 

elastic versus plastic design, 292-293 
elastic waves, 256-257 
flow stress, 269 
force deformation curves, 263 
impact tests, 256, 260-261, 292-294 
impulsive loading, 260-261 
natural strain, 267 


particle velocity in medium, 257 
propagation of plasticity in solids, 
256-261 

rapid loading tests, 256, 265 
rupture of materials, 267 
strain rate tests, 255-256, 265 
tensile impact tests, 256, 264-265 
true stress, 267, 269 
unstressing, 258-259 
Supersonic wind tunnel, design prob¬ 
lems, 251-254 

Surface waves, explosion generated 
effect on mines, 32 
measurement of, 59 

T-44 frangible bullet, 242-248 
ballistic coefficient, 242 
evaluation, 248 
limit velocity, 242-243 
limitations in aerial gunnery training, 
247 

performance on glass, 244 
propellant, 244-245 
range, 242 

use with K-15 sight, 246 
use with piston gun, 245 
Tank hose (line charge), 102, 105 
Tank protection against shaped 
charges 

plastic armor, 280-281 
spikes on panels, 281 
Target airplanes for aerial gunnery 
training, 245-246,-248 
Target damage techniques, 310-333 
air blast, 311-312, 328 
confined blast, 312, 328-329 
cratering attacks, 327 
equivalent horizontal area for sloping 
target, 454 
external blast, 328 
fire, 315-316, 328 
force requirement, 317-318 
fragmentation, 314-315, 326 
mining of harbor entrances, 327 
prediction of damage, 310-311, 319 
radius of damage, 314-315 
shadow ratio chart, 452-453 
training of operations analysts, 339- 
341 

underground explosion, 312-313, 321, 
327-328, 330 

underwater explosion, 313-314 
weapon selection, 319-333 
Target vulnerability, 318-333 
air transportation, 326-328, 445 
domestic construction, 284-285, 330, 
456, 459, 463, 465-467, 469 
industrial targets, 328-333, 436-437, 
460-462, 464, 468, 471-472 
Japanese steel industry, 331-333 
military targets, 319-324, 441-442 
rail and highway transportation, 324- 
326, 446, 448, 457 
steel mills, 438 
underground structures, 323 
utilities, 330 
warehouses, 330 


water transportation, 327-328, 439, 
447 

Taylor Model Basin 

air-blast measurements, 65 
cables for electrical pressure gauges, 
52 

resistor gauge, 51, 71-72 
Telecon (British) cable, 118 
Tellermine, 43; 103, 106 
Tensile testing machines, 263 
Terminal ballistics 
see Ballistic studies 
Testing materials, machines 

see Machines for testing materials 
Tetryl charges 

destructive effect, 46-48, 284 
properties and uses, 359 
tetryl booster, 66, 93 
Tetrytol, properties and uses, 359 
Thompson, J. J., shock wave pressure 
measurement, 50 
TMi-43 (tellermine), 103, 106 
TNT 

peak pressure and positive impulse, 
78-79 

properties and uses, 359 
Torpedoes 
aerial, 308, 368 
Bangalore, 309, 323-324 
carpet-roll, 102 

effect on water transportation, 327 
Torpex 

aluminum content, 79 
bubble period, 35 
composition, 20, 78 
effective range, 35 
explosive effect, 79 
properties and uses, 359 
sensitivity, 35 
torpex D-l; 79 
underwater weapons, 20 
Tourmaline gauges 
advantages, 51 
calibration methods, 38-39 
description, 50, 70 
sensitivity, 70 

Trauzel lead block test of explosives, 
65 

Trialen, 78-79 
Tritonal 

aluminum content, 79 
composition, 20, 78 
evaluation, 92, 94, 127 
explosive effect, 79 
properties and uses, 359 
Tungsten carbide projectiles 
angle of attack, 179 
ballistic coefficient, 169 
bend strength, 184 
effect of projectile cap, 187 
effect on German tanks, 189 
perforating ability, 176, 185, 408 
stability, 170 
standard length, 185 
striking velocity, 178 
types, 188 

UERL spring-piston gauge, 72-73 


MHIkvti yi£ 





512 


INDEX 


Underground explosions 

see Explosions under ground; Shock 
waves in earth 
Underwater explosions 

see Explosions under water; Shock 
waves under water 

Underwater Sound Reference Labora¬ 
tory, 39 

U. S. Naval Bomb Disposal School, 340 
Universal indicator mine, 102, 10G 
University of Illinois, 288 
University of Pennsylvania, 255 

V2 rocket, 309 

Von Neumann, reflection of shock 
waves, 83-85 

VT (proximity) fuzing, 82, 87 
Watertown Arsenal Experimental Lab¬ 
oratory, 255 


Weapon data sheets, 342-354, 357-472 
Weapons, airborne, 307-308 
Weapons, artillery, 308-309 
Weapons, effectiveness, 305-307, 309- 
311 

mean area of effectiveness, 309-311 
methods of studying, 305-307 
prediction of damage, 309-311 
radius of damage, 310-311 
recommendations for future work, 
333 

Weapons, selection principles, 319-333 
airborne rockets, 320 
AP bombs, 322 
artillery projectiles, 321 
cratering bombs, 327-328 
delay fuzed bombs, 322 


fragmentation bombs, 320, 327-328, 
330 

GP bomb, 321-332 

high explosive bombs, 329 

incendiary bombs, 320, 330 

instantaneously fuzed bombs, 323 

LC bomb, 330 

line charges, 323-324 

rockets, 321, 323, 328 

SAP bombs, 325, 329, 332 

torpedoes, 328 

Westinghouse Research Laboratories, 
255 

Williams gauge, 73 

Wind tunnel, supersonic, design prob¬ 
lems, 251-254 

Woods Hole Oceanographic Institution, 
62 

Wright Field, Ohio, 242 


















































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